# carb adjusting



## Chris-Austria (Dec 23, 2010)

Hi!

I had the chance to drive my car today and it was the first time I pushed the pedal a little further.
It feels like at about 4500rpm it leaks power, the acceleration with my camshaft should be in it's power range at this rpm but it seems to have more power underneath.

Do you think it does not get enought fuel? 
It's a stock Holley Ultra Double Pumper.. so maybe I need to change the power valve? How do I know which one to use? Or do you think it's because of jetting or my fuel pump which puts out about 5psi, at full throttle maybe a little more? Where should I start my search? 

From idle up to about 4500 it makes good power, can't say the camshaft is too big.. it also has a nice idle now with the Holley carb (instead of the tri-power).

(435cui, 4speed, raiv4 cam, e-heads, 10.6:1 cr, headers, Performer manifold..)

Hope someone can tell me what I should try first.

Chris


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## Rukee (Feb 8, 2007)

What CFM is the carb?


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## Chris-Austria (Dec 23, 2010)

750cfm.. maybe it isn't big enough for 6500rpm, but at 4500rpm I guess air cannot be the problem.. It's a 435 mildly built and max rpm is 6000 (or even 200rpm less)
http://www.carburetion.com/calc.asp => 717cfm is what I need with 6000rpm and at 4500rpm it's only 481cfm.. would be very surprised if the carb is too small


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## BearGFR (Aug 25, 2008)

Hey Chris, I'm not all that familiar (translation: not familiar at all) with how Holleys act when they run out of gas. In my car with the QJet, it's quite abrupt - like someone turned off the ignition. Perhaps a Holley with the larger fuel bowls acts differently though.

Something you could try: go a little larger on the jets, say just one, maybe two numbers larger. If that causes it to start nosing over at a lower rpm, then it's probably fuel starvation (larger jets will let it pull the fuel supply down sooner). If not, or if it seems to get a little better, then the motor's telling you it wants a richer mixture.

Bear

Edit: or you could do what I finally did and get yourself one of these:
http://thmotorsports.com/i-531324.a...type=pla&kw=&gclid=CLfUscqDq7YCFZGiPAodZhQAdw

I'm waiting for it to come in.


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## Chris-Austria (Dec 23, 2010)

That air/fuel meter would be really nice, but a little bit expensive 

Do you think I should try the bigger fuel pump first? It's cheap and maybe it solves the problem. The stock pump has 40gph and the Holley or Edelbrock has 110gph.

Another question would be.. go with the Holley or Edelbrock? Both seem to have the same "power" but the Edelbrock has 3/8" inlet/outlet and the Holley only 1/4".
If Edelbrock pumps are okay, I'd prefer this one because of the inlet/outlet size + they say it's capable of supporting up to 600hp.. so if it doesn't change anything I know the fuel pump can't be the problem.

And what's the deal with the 2 or 3 port on the pump? My old pump has 3.. I think one is a return line?!
Edelbrock and Holley both have only 2 ports, one inlet, one outlet. Will this work with my car?? Can I clog the third port (respectively the line)?


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## ALKYGTO (Mar 29, 2010)

Do you have a fuel pressure gauge? Need to see if you are maintaining pressure before you swap out pumps.

Read the plugs, lean? white is lean.

What power valve do you have in there now, they are rated at vacuum (ie 6.5)

What valvesprings are you using? Did engine builder put lighter springs in for break-in? 

Do some online research into tuning Holley carbs or buy a good book on the subject, just my 2 cents. :cheers


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## Chris-Austria (Dec 23, 2010)

Hi!
I've been to the shop some hours ago and he checked the carb. Power valve is matching my vacuum he said and the carb is tuned. I read that stock Holleys use a 6.5 power valve... it wasn't changed. My vacuum at idle is about 12" and if the engine is at WOT it wouldn't be much of a differnce I guess?! But if you think another power valve could help please let me know! He also said the float levels are good but he can't say if there is enough fuel at high rpm under load. I could test it on a Chassis dyno (200 Dollar) or first try it with a new fuel pump (150 Dollar).

He also checked my old fuel pump. It's a stock model, 40gph. Pressure is between 3.5 and 4.5 psi. He said pressure will not increase with rpm, so I never will have the 5-7psi that are recommended by the carb manual.

For break in only the outer springs have been used plus the grease and additive on the camshaft/oil. Now I changed the oil to 15w40 with zddp additive (after 50 miles).
I use the valve springs that came with the Edelbrock head and stock size rocker arms (1.5 ratio). Camshaft is the 041 from Comps (230/240 @0.05)

Plugs are not lean, but I didn't drive the car at high rpm's.. if I cruise around and use up to lets say 3500rpm plug reading is good.. if there is a tendancy than its a little on the rich side, but not much.


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## Chris-Austria (Dec 23, 2010)

Another question.. I'm about to build the new fuel lines but don't know where to place the pressure gauge

I can place it like shown on my picture or I could place it right of the Tee-Fitting. There would be a third choice to cut the fuel hose to the pump and use an 3/8" to 3/8" adapter with a 1/8" npt port for the gauge.. but I don't really like the idea.

What do you think?

Here is the picture:


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## Chris-Austria (Dec 23, 2010)

What do you think of the spark plugs? One from each side (#4 and #3)


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## geeteeohguy (Feb 2, 2008)

The plugs look good. A little lean, if anything. Bear gave me my "grin for the day" when I saw what he ordered. No surprise there! Nothing better than an 02 sensor system to really dial in a fuel system.....all post '79 domestic cars use it. If anybody's cruising the Dallas Texas, area, watch out for the guy with the pocket protector in the black '69 GTO.....he's dangerous!!


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## Chris-Austria (Dec 23, 2010)

The plugs first have been a bit more black than white... now they are brown with a white touch, don't know why. But I also think that the air/fuel might be okay now. Bear has ordered a real nice system.. I also like his fuel pump which seems to have the power to pump the fuel faster into the carb than it can be refilled at the gas station 

Any thoughts on the pressure gauge location, or does it not matter where I place it?


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## ALKYGTO (Mar 29, 2010)

Pressure gauge should be mounted after the regulator.

If you are only getting 3.5 to 4 psi out of the pump then i would replace the pump, a regulator will not increase the pressure, it is only made to "regulate" or keep it the same. Your pump needs to put out more and the carb should have at least 7 psi to it. To me the whitish looking plug is definitely lean. I like the pump Bear ordered and you should consider that as an option.

If you can dyno tune i highly recommend it. Make sure the dyno is equipped with an O2 sensor so you can monitor the A/F ratio throughout the power-band.


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## Chris-Austria (Dec 23, 2010)

Thanks for the info.
The manual of the new pump (110gph, 6-7psi) says that I dont need a regulator.. at the moment there is no regulator as well. Should I get one? And without the regulator it wont make a difference where I place the gauge? Also Holley says that my carb wants fuel pressure between 5-7psi.. my engine is far away from the power of Bear's engine.. maybe it will make something between 400-450hp.

With the new pump and lining in place I will go to the dyno with the O2 sensor to check the mixture and fine-tune it. The plugs before have been really white (as long as I used the tri-power). Is it possible that it needs some time to get rid of the white "parts" on the plug even if the mixture now is okay?


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## ALKYGTO (Mar 29, 2010)

If you are running a mechanical pump with a return line you should be okay without a regulator but definitely recommend a gauge. If no regulator it wont matter where you hook it up. 

Plugs will read after only a little bit of engine cycling/ running time. Best way to read is actually go WOT and then shut the motor off and read. Reason is that you can be lean at idle, rich at WOT or part throttle, rich at idle, lean at part throttle and lean at WOT or any other combination. That is why dynoing with an O2 sensor is very important. You are not just tuning for WOT or looking for a big number up top but tuning for the entire RPM range. I've seen cars pick up more power in the mid range and keep the same max HP. Also pick up better drivability and idle characteristics I would definitely ask for references from your tuner from other customers if you can.


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## Chris-Austria (Dec 23, 2010)

The aftermarket pumps all have only one inlet and one outlet. Both the Holley and Edelbrock manuals say "a regulator is not needed" anyway.
If I don't use the return line, I should use a regulator to avoid vapor lock or just because to avoid too much pressure?

The dyno with O2 would be very nice, I'll fine tune my engine there if they can do it (the only dyno with O2 in my region is the one from the Porsche shop and they are pretty expensive).

If the plugs read after only a short time I'll have to test them again because the engine idled for maybe a minute before I switched it off and checked the plugs.


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## geeteeohguy (Feb 2, 2008)

A regulator won't help with vapor lock. A return line will. A regulator just keeps pressure under control....it won't keep fuel from percolating at a usable pressure.


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## Chris-Austria (Dec 23, 2010)

Okay so I can't see why I would need a regulator as the pump gives constant 6-7psi.
The only problem is that both pumps (Holley and Edelbrock) don't have a 2nd output for a return line, so there is no way to connect one. Why would they do this if it will cause trouble at customer's cars? Or will vapor lock only be a problem in very hot climate or if the fuel lines are routed along some very hot engine parts? 

As I won't be able to connect the return line I will make an insulation that divides the pump from the engine's heat and the use of hard lines will also help cooling the fuel I guess. It's routed where the big electric fan blows air, so maybe it will help with cooling. Also the weather where I live is not that hot in summer.. 90° is about the most it will get and my cooling system keeps the engine at 160° if I want it to even in traffic on hot days. (I'll set my engine temp at 180-195° this summer)

Would there be a way to connect a return line to a Edelbrock fuel pump with only one inlet and one outlet? I guess not but I may be wrong


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## BearGFR (Aug 25, 2008)

I like this pump:
RobbMc Performance Products - Pontiac 550HP Fuel Pump

with the optional fitting for a vapor return line.

RobbMc makes great quality parts and they are terrific to deal with. In my experience, they go beyond what they have to in order to make things right.

Bear


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## geeteeohguy (Feb 2, 2008)

Or, you can install a vapor return line like the '66 and early '67's had, like the one on my own '67. It comes off of the fuel filter which is installed on the intake behind the T stat housing/alternator. It's a large, canister filter with one inlet and two outlets. You'll need the filter, bracket, and return line section, all available from the vendors.


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## BearGFR (Aug 25, 2008)

Seriously Chris, we all have our favorite ways of setting these cars up. There's no "one right way". I'm guessing your climate at home there is quite a bit different from mine here in Texas, so you may never have to deal with a vapor lock problem. Sound like to me your main issue is getting consistent and sufficient fuel pressure to provide enough fuel delivery to the carb, which may currently be a little on the lean side. Getting that dealt with is what matters, the "how" isn't all that important as long as it works for you.

Bear


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## Chris-Austria (Dec 23, 2010)

I would love to have a climate like in Texas.. but it's never really hot where I live. Probably I won't have any problems with vapor lock. Will I need to have such a fuel fiter or can I just use a T fitting on the way to the carb (somewhere near the pump) and connect it to the already existing return line? If I don't lose too much pressure I might think of it if I will have problems with vapor lock in summer.

Bear you are right, I just want to give the engine enough fuel if I rev it up to my 5800rpm limit. Checked it again today and fuel pressure is never more than 4.5psi and as I have a stock pump it's 40gph. The pump you recommend is surely a high quality part, but I already ordered the Edelbrock pump with 110gph and 6-7psi. They say this pump supports up to 550-600hp.. my engine will not produce more than 450hp with the best setup I guess.

I hope it works for me and I'm looking forward to fine-tune it (after I got the new pump and lines installed).
Thanks for all the information, I really appreciate it (even if I use another pump..) I now know what to do if vapor lock becomes a problem and I hope the pump I choose is adequate for the engine's needs (like I said.. I don't race.. if it can support the few times I rev it up to 5800 I'm happy.. there will be no long time high rpm driving)

If you want to hear the difference between the "bad" tri-power and the Holley carb, I will add 2 videos. Nothing has been changed except the carbs (and manifold)

Tri-Power





Holley Double Pumper


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## ALKYGTO (Mar 29, 2010)

Chris, it sounds to me like a bypass regulator is what you want/need. Something like this -

Aeromotive 13301 Bypass Fuel Pressure Regulator, 3-60 PSI - Speedway Motors, America's Oldest Speed Shop

Basically this regulates the desired pressure and bypasses the excess fuel back via your return line. This one is high quality but slightly pricey at $135 from Speedway. There may be cheaper ones out there. This one has one inlet and three outlets so one to each bowl on your carb and one to the return line.


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## Chris-Austria (Dec 23, 2010)

This bypass regulator has everythink I might need. Looks really nice!! (funny that it is more expensive than the fuel pump itself).
If I will experience any problems with the "fuel pump only" I will get something like that! Thanks for the information, didn't know somethink like this is available.
My only concern is.. this regulator cannot improve gph or psi and the fuel pump will deliver the optimal pressure by itself. So do you think it would be "better" than a self-made bypass for.. $5?


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## ALKYGTO (Mar 29, 2010)

Chris-Austria said:


> So do you think it would be "better" than a self-made bypass for.. $5?


Yes.


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## Chris-Austria (Dec 23, 2010)

Okay  With the self made bypass I'm only a bit afraid of the pressure loss because of the return line that (as I think) will get as much pressure as the line to the carb...so both will loose. If there will be a need for a change I won't safe the money and make it right!
Did I get that right that the expensive bypass regulator's purpose would mainly be to keep my fuel cold and prevent vapor lock? (because the pump's pressure doesn't need any "regulation")
Does it have an advantage if I can use two of the outlets from the bypass to connect both fuel bowls seperately? And why?


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## BearGFR (Aug 25, 2008)

The advantage of using to outputs, one for each bowl, is that you get parallel flow --- instead of feeding the whole carb through one 3/8" line, you're feeding it through two --- less restriction to flow.
Another trick you can use is that if you find the return line off the filter is causing too much pressure drop to the carb, add a restriction to the return line.

Dramatic difference in your two videos -- what I surmise from it is that your tripower idle circuit was extremely lean.

Bear


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## Chris-Austria (Dec 23, 2010)

Right Bear, the idle tubes would have needed a lot of modification and no one really wants to do it here. Maybe some other things would need improvement, that's why I now use the Holley.. it ran good out of the box and with some small modifications it's now as good as possible without using an O2 sensor. This is what I will do after the fuel delivery is improoved. Maybe I need a little bigger jets. The power valve (6.5) should be good for my 12" vacuum at idle (I was told.. if you disagree please tell me).

The difference between the two videos is big.. what I learned is that a good air/fuel mixture is essential! I'm also happy that I choose the RAIV cam and not a smaller one. It sounds and feels good, 230/240 @0.05" isn't too much for a street driven 435.. not at all!!


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## ALKYGTO (Mar 29, 2010)

Chris-Austria said:


> Okay  With the self made bypass I'm only a bit afraid of the pressure loss because of the return line that (as I think) will get as much pressure as the line to the carb...so both will loose. If there will be a need for a change I won't safe the money and make it right!
> Did I get that right that the expensive bypass regulator's purpose would mainly be to keep my fuel cold and prevent vapor lock? (because the pump's pressure doesn't need any "regulation")
> Does it have an advantage if I can use two of the outlets from the bypass to connect both fuel bowls seperately? And why?





BearGFR said:


> The advantage of using to outputs, one for each bowl, is that you get parallel flow --- instead of feeding the whole carb through one 3/8" line, you're feeding it through two --- less restriction to flow.
> Another trick you can use is that if you find the return line off the filter is causing too much pressure drop to the carb, add a restriction to the return line.
> 
> Dramatic difference in your two videos -- what I surmise from it is that your tripower idle circuit was extremely lean.
> ...


^ Agree with Bear and ......run a regulator. Seriously.


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## Chris-Austria (Dec 23, 2010)

Looks like there are some good advantages with the bypass regulator. I'll get one next time I order something from the US.

For the time in between what do you think of the idea with a bypass just behind the pump outlet and connect the old return line there? Will I loose too much pressure by doing it? If I would use the fuel filter with the return line it would almost be the same I guess? (I don't want to have not enough fuel at the carb just because of the return line of which I'm not sure that I need it)

edit:
I just found out that the filters with the return line on the 66 GTO are "with AC" and the models without AC had the "normal" filter and a fuel pump with one inlet and one outlet like the Edelbrock or Holley pump (no return line). Also my engine runs colder than a stock engine, maybe because of the aluminum intake, aluminium heads, 3" radiator and big electric fan. 
At which situations vapor lock is likely to occur? If my engine never runs hotter than 195° (even in traffic) and the fuel hoses are isolated from the engines heat is there a big chance to get into vapor lock situations? How much fuel temp is needed to create vapor lock? Where I live the temp is 95° max in summer.. most times it's colder! (in the 80-85° range).


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## Chris-Austria (Dec 23, 2010)

A little update:

I'll use this filter for now: http://static.summitracing.com/global/images/prod/large/WIX-33041.jpg

It has 3/8" inlet and outlet and 5/16" fuel return. I'll build my own carb inlet lines with the pressure gauge adapter and run a 3/8" hose to this filter and 3/8" into the new Edelbrock pump. So every line and hose for fuel delivery has AN 6 (3/8") I.D. and the return is like before 5/16". Pressure will be in the 5.5 to 7 psi range with the 110gph pump. That's a lot more than before, will look nice and keep my fuel as cold as before (never had vapor lock issues). 

I'll show it to you next week and just wanted to thank everybody for the input! Maybe I'll upgrade some time to the really good pump Bear showed me and use the pressure regulator, but only if there is a need or improvement by doing so. If the system now will work as supposed to I'm pretty happy and could safe half the money. Rebuilding the engine was more expensive than I thought anyway and I don't think this sollution is "bad".. 

I also finally know my rear gear ratio since today.. it's 3.55:1  First I was a little afraid of the RAIV cam, but it runs really great and the gears are okay I guess (was told that 3.9:1 would be recommended or higher).


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## Chris-Austria (Dec 23, 2010)

the new self-made tubing:









Next time I order parts from the US I'll get the fittings to build the line all the way down to the fuel pump.


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## BearGFR (Aug 25, 2008)

Nice work, Chris.

I'll tell you though - I'd sure think long and hard about using that much rubber line. In fact, I'd think long and hard about using -any- rubber line anywhere in the system 

Fuel leak induced engine fires are very very bad...

Bear


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## Chris-Austria (Dec 23, 2010)

I absolutely agree!
The line will be improved again, but the most critical part is now finished (rubber lines connected to non-flared tubing).
I will have to think about the return line if I use all metal tubing, because the inline filter with return can only be connected to soft rubber lines. 

Is it bad to use the fuel filter directly after the fuel pump? If I use this filter near the water pump it will look very ugly


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## Chris-Austria (Dec 23, 2010)

Yesterday I found out that I need a return style system. The engine stumbled a bit after I drove about 1 hour if I wanted to accelerate. I stopped and checked my fuel filter (glass) and could see that there are more bubbles than fluid.

So I let it cool down, drove it home and build this:









Works great, but now I even have more rubber lines. I want to get rid of them all and use a bypass regulator for the return system.
Will these regulator only return the fuel if it isn't needed? Like at lower rpms? Or do they return the fuel all the time like the construction I have now?

The return line size now is 5/16" and is located on top of the filter.. I guess it will not flow that much back but it's enough. If I use a regulator, should I use the same size for return as for the rest (3/8")? And where can I mount the regulator to make it look and work good? I guess I have to mount everything directly on the engine so that the lines cannot break because of movement?!


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## ALKYGTO (Mar 29, 2010)

Ok, *first*, as we have *ALL* said, please, please, please get rid of all the rubber hose. 

Second, you can run a regulator anywhere between the pump and carb. The setup you have is.....not good. Fluid is going to go the path of least resistance so it's going to want to bypass naturally with that setup, at least from what I can see and that will starve the carb and engine.

RUN A PROPER BYPASS REGULATOR my friend. Spend a little now and save yourself some heartache and trouble later on. I only say this because I really want to see you enjoy your car and have no troubles. I've given you some suggestions for return regulator setups at the high and low end, any of them will work for you.

Go get some braided #8 line to replace that hose or even some steel hardline ( I don't like aluminum on a street car because it is suceptable to fatigue/cracking) or some Earls pushlock hose with the proper fittings (thats what I run). The Earls hose is "rubber" but industrial strength stuff with a teflon liner and 250 psi burst strength and the pushlock fittings are used on Top Fuel dragsters and "Funny" cars.

Aeroquip Socketless Hose- Black and Blue Socketless Hose


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## Chris-Austria (Dec 23, 2010)

I wanted to build the line (metal) but didn't have the time since. I only replaced the part directly into the carb as this was really dangerous before.

I have your suggestions on my wish list at summit, now I'm about to choose one and build the line but I cannot build a stainless line by myself, I only have the tools for aluminium. Do you think it won't be reliable? The really old tri power lines are made from aluminum and are still good.

The rubber hoses you mentioned should also do the trick if you think they are better than aluminum I may get these instead.

I'll keep my #6 line size since the line from the tank isn't bigger and the inlet/outlet from the pump isn't bigger, but should I use a 3/8 or 5/16 return? The return line from the tank to the front of the car is 5/16.. that's why I wanted to buy something like this if you agree:

1. http://www.summitracing.com/parts/hly-12-803bp
2. http://www.summitracing.com/parts/sum-230103
3. http://www.summitracing.com/parts/sum-g2538

I wanted to mount the regulator to the engine where it isn't visible and make a hard line connection with no rubber at all from the pump up to the carb and a hard line for the return that will lead into a flexible hose just to connect the undercar line to the return line. Do you think this should work? Because I want to get rid of the rubber and order the items I need. Probably I'll have time to build it at end of June.


But.. I tried this setup I build carefully (took me about 1 hour) and there is no starving at all. I don't know how much it returns, but the fuel pressure gauge (after the filter) shows constant 6psi. (before it was 6-6.5psi). It didn't starve at WOT, didn't starve on the highway (90mph) and best of all it didn't start to stumble because of vapor lock like before. But I don't want to convice anyone that this setuip is "good"... but it works until I replace it in 5-6 weeks with the proper metal lines and regulator.


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## ALKYGTO (Mar 29, 2010)

That will all work but if you do use the aluminum line be sure to run insulated mounts to protect it from movement and vibration. I agree on the 5/16" return line typically you want that smaller than the feed line. You can engine mount the regulator since you have a mechanical fuel pump. 

Sorry if I came off harsh Chris, I just don't want to see you lose that beautiful GTO. I'm sure Bear would agree with me that an engine fire is just about the worst thing that can happen to a car. You can lose everything in no time at all.

Please carry a fire extinguisher either way, buddy. :cheers


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## BearGFR (Aug 25, 2008)

ALKYGTO said:


> That will all work but if you do use the aluminum line be sure to run insulated mounts to protect it from movement and vibration. I agree on the 5/16" return line typically you want that smaller than the feed line. You can engine mount the regulator since you have a mechanical fuel pump.


:agree The thing with aluminum is it will work-harden from vibration/movement. When that happens it gets brittle. When it gets brittle it tends to crack, and leak, with disastrous results.  If it were me, I'd use steel instead of aluminum - especially on a street driven car.



> I'm sure Bear would agree with me that an engine fire is just about the worst thing that can happen to a car. You can lose everything in no time at all.


:agree Uh, yeah... "Fire" is a 4-letter word for a reason. A couple nights ago, I came in from the garage and said, "Honey, well it fired up ok." Here eyes got big and she started looking all worried - then I realized what I'd said. I think I'm going to quit using that word. :willy:



> Please carry a fire extinguisher either way, buddy. :cheers


Amen to that!

Bear


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## Chris-Austria (Dec 23, 2010)

Thanks  I always have a 2kg fire extinguisher with me. I appreciate that you care about safety, no problem with that!
A friend of mine helps me build the line and he uses something for the connections that I cannot translate, but its for the purpose you said (no leaks even if it virates).
I either use the parts mentioned above or the fuel pump Bear told me (but the small 550hp version with vapor return) in conbination with an all metal lining from the pump to the carb!
Glad to know my options and how it works!!


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## Chris-Austria (Dec 23, 2010)

I have another question...

Will a bypass regulator like the one above reduce the fuel pressure from my pump? If it will reduce the pressure about 1psi, do you think 5psi will be enough for my Holley carb?
The other option would be to get a RobbMC fuel pump (550hp) that will produce about 7psi (max. for my carb). But if I order this pump with vapor return it will give about 6psi to the carb, which seems to be perfect.
I don't want to build a line, use the bypass regulator with the Edelbrock pump and after all the work and money have not enough fuel pressure for higher rpm's like I had with the stock pump that was at about 4.5psi.

My idea is:

1. use the RobbMc 550hp pump with vapor return and 3/8" ports
2. connect the inlet and vapor return from the pump with the undercar lines with a Earl's rubber hose for flexibilty
3. build a hard line from the pump outlet up to the carb with a in-line fuel filter like the one above

I'm sure this will work great.. but it will cost much more than just use a bypass regulator.. what do you think? Should I get the new pump or will the cheap solution with the bypass work as well?


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## BearGFR (Aug 25, 2008)

Hey Chris,

Whenever you're designing something like a fuel delivery system it's important to pay attention to both the concepts AND the recommendations from the specific vendors that you're planning to use. For example, the RobbMc pump specifies NOT to use a bypass mode regulator, but to use a 'dead-head' regulator instead.

In general though, the purpose of a regulator is to "regulate" the output pressure of the pump. This assumes that the pump is providing more pressure to the input side of the regulator than the regulator is supplying out to the carb (otherwise, why would you need a regulator at all?). Think of the regulator as a 'throttle' for the pump - they're adjustable. So when you install a regulator you adjust it so that the output pressure is what you want supplied to the carb. In bypass mode, the "excess" fuel (however much there might be) is routed through the return line back to the tank. This is the reason you have to be at least a little concerned about the size of your return line. If it's too small, and the pump output pressure too high (compared to the regulator setting) it won't be able to handle the volume of fuel that's being shunted back to the tank and you'll have problems. In dead-head mode, a regulator just "turns off" the pump output without having to "do anything" with excess fuel. Mechanical pumps (at least the RobbMc pumps) are designed to deal with this situation with no ill effects. "Most" electric pumps can't and would be damaged pretty quickly with a dead-head regulator. It gets a little confusing because RobbMc puimps/regulators have an option to run a small vapor return line even with a dead-head regulator, but this setup won't pass enough fuel to run an electric pump that needs a true excess fuel return.

There's more here than meets the eye and it gets confusing because the same terms are used to describe different things:
A "vapor return" line for a mechanical pump is NOT the same thing as a "vapor return" line for an electric pump.
A "regulator" for a mechanical pump is (generally) not the same thing as a "regulator" for an electric pump.

Your engine doesn't know or care about the details of your fuel system and what parts are in it. All it cares about is keeping the fuel bowls in the carb full - it doesn't care how you do that.

I'm running the "big" RobbMc 1100 hp mechanical pump on my car, which should be way more than I'll ever need. In fact, by all rights the 550 ought to be plenty big enough for my car. I tried really hard to do everything "right" - I put a rear sump in the tank and relocated the fuel pickup there, I've got larger than stock fuel lines (either 1/2" stainless or -8AN braided steel hose) all the way from the tank to the carb. I've got a big RobbMc 100 micron filter in the line back by the tank and a big RobbMc 40 micron filter at the carb inlet. I'm running a RobbMc dual mode regulator (in dead-head mode) set to 7psi output pressure. The pump itself is putting out about 11 psi into the regulator. There's no exposed rubber hose at any point in my system, even on the smaller vapor return line coming off the regulator - the flexible connections between the regulator and the 1/4" hard line running down the front of the block, and from between that hard line and the long vapor return line running through the frame are both -5AN braided steel.
Sound good? It did to me too, and I spent some significant coin building all that. I wanted everything over-engineered so there'd be no way I'd ever have to worry about fuel delivery issues. .... Yet, the last time I went to the track I had (guess what) a fuel delivery issue. That's the problem I was trying to solve several weeks ago when I experienced the fire. :willy: So when I put it all back together this time, I changed a few things trying to improve areas that I thought "might" have been contributing to the fuel delivery problem, but I won't know for sure if I was successful until the next time I take it to the track.

Moral of the story: 
There are no guarantees when you're working with these cars. If I can't (apparently) build a reliable fuel system working directly with all the "best" parts I can find and not hesitating to spend the cash, then it's not likely that anyone is going to be able to "tell" you something that's guaranteed to work first time every time no matter what without ever even seeing your car. The best we can do is make recommendations for things to try, things that make sense. But in reality, what's probably going to happen is that you're going to have to spend some time, effort, and cash "messing" with it until you find the magical combination that's right for your car and your situation, and don't be surprised or disappointed when you don't hit it the first time and wind up "wasting" money on false starts. That's just the way it goes.

Bear


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## BearGFR (Aug 25, 2008)

Hey Chris,

Whenever you're designing something like a fuel delivery system it's important to pay attention to both the concepts AND the recommendations from the specific vendors that you're planning to use. For example, the RobbMc pump specifies NOT to use a bypass mode regulator, but to use a 'dead-head' regulator instead.

In general though, the purpose of a regulator is to "regulate" the output pressure of the pump. This assumes that the pump is providing more pressure to the input side of the regulator than the regulator is supplying out to the carb (otherwise, why would you need a regulator at all?). Think of the regulator as a 'throttle' for the pump - they're adjustable. So when you install a regulator you adjust it so that the output pressure is what you want supplied to the carb. In bypass mode, the "excess" fuel (however much there might be) is routed through the return line back to the tank. This is the reason you have to be at least a little concerned about the size of your return line. If it's too small, and the pump output pressure too high (compared to the regulator setting) it won't be able to handle the volume of fuel that's being shunted back to the tank and you'll have problems. In dead-head mode, a regulator just "turns off" the pump output without having to "do anything" with excess fuel. Mechanical pumps (at least the RobbMc pumps) are designed to deal with this situation with no ill effects. "Most" electric pumps can't and would be damaged pretty quickly with a dead-head regulator. It gets a little confusing because RobbMc puimps/regulators have an option to run a small vapor return line even with a dead-head regulator, but this setup won't pass enough fuel to run an electric pump that needs a true excess fuel return.

There's more here than meets the eye and it gets confusing because the same terms are used to describe different things:
A "vapor return" line for a mechanical pump is NOT the same thing as a "vapor return" line for an electric pump.
A "regulator" for a mechanical pump is (generally) not the same thing as a "regulator" for an electric pump.

Your engine doesn't know or care about the details of your fuel system and what parts are in it. All it cares about is keeping the fuel bowls in the carb full - it doesn't care how you do that.

I'm running the "big" RobbMc 1100 hp mechanical pump on my car, which should be way more than I'll ever need. In fact, by all rights the 550 ought to be plenty big enough for my car. I tried really hard to do everything "right" - I put a rear sump in the tank and relocated the fuel pickup there, I've got larger than stock fuel lines (either 1/2" stainless or -8AN braided steel hose) all the way from the tank to the carb. I've got a big RobbMc 100 micron filter in the line back by the tank and a big RobbMc 40 micron filter at the carb inlet. I'm running a RobbMc dual mode regulator (in dead-head mode) set to 7psi output pressure. The pump itself is putting out about 11 psi into the regulator. There's no exposed rubber hose at any point in my system, even on the smaller vapor return line coming off the regulator - the flexible connections between the regulator and the 1/4" hard line running down the front of the block, and from between that hard line and the long vapor return line running through the frame are both -5AN braided steel.
Sound good? It did to me too, and I spent some significant coin building all that. I wanted everything over-engineered so there'd be no way I'd ever have to worry about fuel delivery issues. .... Yet, the last time I went to the track I had (guess what) a fuel delivery issue. That's the problem I was trying to solve several weeks ago when I experienced the fire. :willy:
So, while I was putting the car back together I tried to "improve" some things that I thought "might" have been contributing to the fuel problem but I can't say for sure if they've done any good or not until the next time I take the car to the track - and even then there won't be any "proof" that they were the cause.


Moral of the story:
There are no guarantees when it comes to these cars. Sometimes despite your best effort, things will just refuse to work correctly anyway. Don't be surprised when you wind up having to spend additional time, effort, and cash to "mess with" your fuel system until you manage to find the right magical combination that works on your car. No one sitting at a keyboard many miles away is going to be able to hit that combination for you on the first try. The best we can do is try to help you through the obvious pitfalls and try to minimize your "pain" --- but there's going to be some of that no matter what.
It's all part of the "fun", right? :rofl:

Bear


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## Chris-Austria (Dec 23, 2010)

Hi Bear,

I just sent an E-Mail to RobbMC and asked what they think of my "idea". I'll probalby try it with their 550hp pump that has an output of about 7psi or 6psi with return option. They tell on their homepage that I don't need a regulator if that is the pressure the carb wants to see and Holley writes that 5-7psi will work perfect. RobbMC also writes that 3/8" will be good up to 450hp and 1/2" is recommended for 550hp. So I can keep my stock lines that are 3/8".

My Setup would be:

- stock gas tank without filter and a 3/8" line to the pump
- stock return line 5/16" that will be connected to the pump
- RobbMc 550hp pump with vapor return
- fuel filter 100microns between the pump and tank 3/8" just 2-3 inches away from the pump
- inline fuel filter on the way up to the carb 6AN from RobbMC 40microns
- 6AN fuel line from the pump to the carb without any rubber Connections

I know you can't guarantee this will be THE setup, but if anything sounds "strange" please let me know. Otherwise I will spend another 300 Dollar for these parts and hope it will be fine. The setup now with the rubber hoses between pump and carb works really great, enough fuel for the carb, no vapor lock, no leaks, 6psi pressure. But everyone who tells me it isn't very safe is right. I coudln't do more than use new rubber lines and clamps with the highest quality that was available in the shop, secure the hoses from touching hot engine parts and use connections that prevent the hose from slipping if a clamp fails.

edit:
I got the information that I have to use the RobbMc fitting for return that is 1/4" and that the pressure with return will be at about 6-7psi which will be just fine without regulator.


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## Chris-Austria (Dec 23, 2010)

Update:

I may take the 1100hp pump from Robb with the vapor return option and a dead head regulator.
Are there any benefits over the 550hp pump for my application? For example will a 14psi pump with a regulator (dead end, set to 7psi) give me more constant fuel delivery or less drop at higher rpm's?
And my last question, is it better to use a regulator with one outlet and split the line to the carb like I have it now or is it better to use a regulator that has 2 outlets and lead each of them seperately into the carb inlets?

RobbMC said the 550hp with vapor option should be good enough.. he also could have said the more expensive pump is better.. but if I can benefit from the stronger pump I'll add the 200 Dollars and get the 1100hp plus a regulator.


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## ALKYGTO (Mar 29, 2010)

Hey Chris, I saw your post before you edited it and I would say any of those regulators would work but I'd be inclined to get all your components from the same manufacturer so If you run the Robbmc pump I'd use their reg. Just my 2 cents and again any of those would work. :cheers

And on your plumbing question I would say either way would work but i prefer personally to plumb with two outlets, one to each bowl on the carb on a Holley aplication.


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## BearGFR (Aug 25, 2008)

Chris-Austria said:


> Update:
> RobbMC said the 550hp with vapor option should be good enough.. he also could have said the more expensive pump is better.. but if I can benefit from the stronger pump I'll add the 200 Dollars and get the 1100hp plus a regulator.


Most of the parts of the two pumps are identical. The difference is that the 1100 has that adjustable plunger on top that controls the action of the pump diaphragm. If the 550 is enough to keep your engine fed, then you won't see any additional benefit from the 1100. It's really just a question of whether or not the pump can deliver a sufficient volume of fuel or not. If you replace the 550 with the 1100 -and- adjust the 1100 to its maximum output, all that's going to happen is that you'll be wearing out regulator parts frequently because it will have to work a lot harder to absorb all that extra fuel pressure/volume from the bigger pump. It might even wear the pump out quicker for the same reason because it's going to be working "against" the regulator most of the time. Also you might have noticed that RobbMc can upgrade the 550 pump to the 1100 pump for what amounts to the difference in price. It's possible because most of the components in them are the same.

I know your situation is a little different because you have to deal with shipping costs and delays that are worse than they are here, and I do understand the idea of getting "more" than you need just to avoid having to solve the same problem more than once, so it's really your call. In the States, with your engine, I'd start with the 550 pump, a dead-head regulator, and then see where that got me. Then if the pump needed to be upgraded I'd do that later.

Bear


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## Chris-Austria (Dec 23, 2010)

@alky

Thank you! Yes I edited the post because I saw the RobbMC dead head regulator that is recommended by RobbMC for this pump. The only option would be the Holley billet regulator that looks really nice and has dual outlet (http://www.summitracing.com/parts/hly-12-840)
I'd like the Holley even more than the RobbMC because of it's look, but I also think buying everything from one manufacturer is better. On the other hand I have a Holley carb.. maybe their regulator isn't a bad choice.. But I guess both will work fine.

@Bear
That's very interesting. Robb sent me the description of the pumps and I'm not really sure if the 550hp will be strong enough. It's 7psi max and I should use 2 filters (100+40mic) and the regulator. This will drop the pressure a little plus the vapor return option will also decrease the pressure (-1psi). I want that the regulator sends 7psi to both inlets of the carb. Maybe the 1100hp pump is better. I saw that it is adjustable, so I can set it to 10psi for example to not wear it out too fast, but by doing so I will always have the proper amount of fuel for my carb.

Like you said... with shipping and taxes it's not fun to upgrade it later.. 100dollar for the upgrade + 120dollar until it arrives at my home. I have the bad feeling that I would Need the upgrade anyway... if not now maybe later when I add a roller cam and port the heads. (I really want to get above 500hp.. but now it was just too expensive..)

I finally know what will work and what my options are. I'll order the parts very soon and I can't wait to get rid of the rubber hoses!!!


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## Chris-Austria (Dec 23, 2010)

I now ordered all the parts for my fuel system. I'll try to build a metal line all the way down to the pump, but maybe this will be difficult. I also ordered a flexibel AN hose that is already assembled. If I cannot build the line from about the alternator down to the pump I'll use the flexible hose to make the connection between the fuel line and the fuel pump.

What do you think of such a hose? Can I safely use it?
http://www.summitracing.com/parts/rus-658510


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## Chris-Austria (Dec 23, 2010)

It's finished.. 550hp pump from RobbMC and all metal lines (one flexible).
It works great, pressure is very good even with vapor return and without regulator. I will Mount the fuel filter with the thermostat housing, will have to build a bracket for this to reduce vibration in the static part of the fuel system.

This is how it looks like:


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## Rukee (Feb 8, 2007)

Nice!!


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## Chris-Austria (Dec 23, 2010)

Thank you!

now with a bracket to reduce vibration:


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## ALKYGTO (Mar 29, 2010)

Nice job Chris! Very professional looking. I'm assuming the thermostat mounting bracket is rubber insulated?


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## Chris-Austria (Dec 23, 2010)

Its a rather soft metal that I bent to fit for exactly this filter (31mm thick) without insulation.. First I wanted to use some insulation but it fits just perfect, better than I thought and it makes no scratches, it wont slip and vibrate any more. 

I cannot build one from stainless steel by myself, but the final bracket will be formed like this one with a rubber insulation because of the hard metal. I'll give my "prototype" to a shop and they can use it as an example.

Maybe if I find the equipment I will build the whole fuel line with stainless steel lines, but nobody over here has got a flaring tool for stainless 37 degree (only 45) so I had no choice but to use alloy.. thats also the reason why I chose a flexible line from the filter down to the pump and build the bracket.

For now I am really happy that there is no more rubber and everything fits and works finally  Making it "better" wont be such a challenge.


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## Chris-Austria (Dec 23, 2010)

here is a better pic:


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## BearGFR (Aug 25, 2008)

Now that's nice.... good job! :cheers

Bear


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## Chris-Austria (Dec 23, 2010)

Thank you Bear. I have to say.. I really waited to read what you think about it 
Tomorrow I'll ask a shop near me to build the bracket from stainless steel. I'll ask what they think.. I'm not sure if I need insulation.. the way it is now fits really good!

Do you know if I can flare the lines to 45° instead of 37° and still have a leak-proof connection (45° ending to 37° ending)


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