# how to adjust my Holley - black spark plugs



## Chris-Austria (Dec 23, 2010)

Hi!

Now that I have my new fuel pump installed (RobbMC 550hp) with vapor return instead of the Edelbrock pump I noticed that if I drive for a while and the engine gets hot it will not run very well if I shut it down, wait half an hour and start it again (today it was 97° and the watertemp was at 205°).
It was a little hard to start again and when I tried to rev it up in my driveway it was stalling. So I tried to avoid higher rpms and got on the street. I reved it up to about 3500rpm and it was nearly stalling again (now while driving). 
After some minutes on the street the problem seemed to be less worse and it didn't feel like when I had the vapor lock problem, but I'm not sure.

What do you think might me the problem? Also the spark plugs are a little black now.. I'll make a picture later.

Is it possible that my engine runs a little too rich now because of the fuel pump? I checked the float levels and they are at almost 3/4 (on the sight windows). Will it run less rich if I set the float level to a litte under middle position like the owner manual recommends?

And is it possible that my fuel bowls get too much heat while the car sits for a while after driving in hot weather? What do you think of carb insulators and which one would fit my Holley DP?

Thanks!
Chris


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## BearGFR (Aug 25, 2008)

The pump won't affect mixture unless the pressure is high enough to 'flood' the carb by forcing the needle off the seat.

Float level (fuel level in the bowls) can affect mixture. "Higher" can result in "richer" because it will then take less of a vacuum (depression) to cause the various circuits in the carb to operate.

Your starting problem could be partially related to heat, and also partially related to an over-rich mixture. (Cold engines like/tolerate richness better than warm engines do). If it were me, I'd focus on getting the mixture right first, then see how it does.

Bear


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## Chris-Austria (Dec 23, 2010)

Thank you Bear!
My plan now is to adjust the float level (turn clockwise for lower if I remember right) and that could lead my engine to run less rich, so I'll start with that and see if anything changes. The pressure now is at almost 7psi.. with the old fuel pump it was 5psi. Maybe this has caused my float level to rise and by that make the engine run richer?! Good to hear that this may be the problem because I can easily check this by myself.
After that I'll have a shop to check/adjust my idle mixture and check the emissions at all rpm's. But before the plugs have been pretty brown.. never black or white.. some looked like they may be a little too cold, but the mechanic also told me they are fine. Now most plugs are black or brown-black.


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## BearGFR (Aug 25, 2008)

With a pressure increase, it does make sense that the floats now have to push "harder" on the needles to shut them and that makes the floats ride "lower" in the fuel. Could be that you're getting close to overpowering the floats, so it'd probably be a good idea to check the specs on your carb and see if they provide a maximum acceptable fuel pressure. If you get to the point where they can't shut off the fuel flow then it's going to start puking fuel out of the vents and that's a bad thing. 

Black(ish) color is an indicator that can mean it's running too rich.

Bear


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## Chris-Austria (Dec 23, 2010)

The Holley's manual says 5-7psi is what they need.
The gauge never shows more than 7psi.. but very close to 7.. before it was very close above 5. (I only can check the pressure at idle and rev it up without being under load)


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## Chris-Austria (Dec 23, 2010)

After I reduced the float level's I drove about 2 hours... and today I was at the shop. The mechanic checked the emissions.. they are as good as before and the plugs now are not black, they look good again.
Thanks for the help!!


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## BearGFR (Aug 25, 2008)

Doesn't it feel good when you make a change, and it actually has the anticipated result? 

Bear


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## Chris-Austria (Dec 23, 2010)

It feels great! 
The HC was at 550ppm at idle and at about 300ppm at about 1200rpm. The CO is about 1,2%. When he reved it up the HC got pretty low.. about 20ppm at high rpm. I should have made a video to ask you if it looks good to you.


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## Chris-Austria (Dec 23, 2010)

Another question.. I want to try an insulator between the intake and carb. 
Do you know if this one will fit? http://www.summitracing.com/parts/hly-108-37
I have the Edelbrock intake and a Holley 4150 Ultra Double Pumper carb.
The 4 holes in the plate.. will they be "good" or is it better without these holes? I couldn't find another insulator...


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## ALKYGTO (Mar 29, 2010)

Do you have a spread bore carb? That is the configuration of the original Q-jet on your GTO (Made by Rochester Carburetor Co.). I think you have a "square bore" carburetor where all four throttle bores are the same size. If so you might consider HVH's Super Sucker. 

Carb spacers are traditionally four hole or "open". The difference are that a four hole increases the length of the throttle bore and increases air speed through the throttle bore and the open increases the plenum volume meaning that the manifold can hold a greater volume of air and support higher RPM levels. I say if you have the hood clearance then I would definitely recommend one.

Super sucker kind of does both and but I would consider asking your dyno operator if he had one of the open and four hole to "try". I know you aren't in the states where this would be a little more likely to happen since he's more likely to have Saab parts than Pontiac. Your beautiful GTO has gotta be a real head turner over there! 

Also the addition of a spacer could affect your current tune and make carburetor adjustments possible. Nice job addressing the carb issues and the float level should always be just above the bottom of the hole. Clear sight glasses are nice (wish I had em!) and when I check mine I remove the brass sight plug and set it (running) until is just starts to run out the hole. On my car at least I don't have to bend over very far but it is a pain with two carbs to set and sitting sideways. 

Here is the link for HVH. :cheers http://www.highvelocityheads.com/ss.htm


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## Chris-Austria (Dec 23, 2010)

Nice descripion of how that works, thank you!
And yes, the GTO is a headturner.. but at the gas station where they can actually talk to me most people only are interested in fuel consumption like it would be the most interesting fact about the car. Someone asked me if it's diesel or gas.. that's why I prefer talking to you guys at the forum about my car  

Back to the topic, I cannot see a link, but I'll search for it. And yes it's a square bore carb, so I will need a plate with 4 holes the same size or open? Most times it isn't that hot over here, but the last days with 95+ degree may be a sign that in summer it will be even more degrees, so I'll take care of that now.
I measured my hood clearence and it's about 3-3,5cm.. so I could raise the carb for about.. 1" or a little more to have enough space and it will not be able to touch my hood.

The sight glasses are really nice and it's easy to set the float level. The owners manual says the fuel should be at the middle of the glass and that's what I adjusted. To set the secondary bowl I reved the engine up a few times to see where it was and after the adjustment to see where it will be now.


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## Chris-Austria (Dec 23, 2010)

I just found out that Summit doesn't sell the HVH spacers.. but I checked their homepage and they look great! Isn't there something like them available at Summit that I could combine when I order new spark plug wires and a header gasket?

edit:
I found these: http://www.summitracing.com/parts/qft-300-4150-1/overview/
Looks like HVH is equal to Quick Fuel. But on their homepage they say aluminium is for street and plastic for race cars. I don't own a race car.. so what do you say? Can I use the plastic one shown above? On their Homepage they also say "The composite spacers offers a thermal brake from the manifold to the carburetor". Is the one that I can get at Summit such a composite spacer??


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## ALKYGTO (Mar 29, 2010)

Chris-Austria said:


> I just found out that Summit doesn't sell the HVH spacers.. but I checked their homepage and they look great! Isn't there something like them available at Summit that I could combine when I order new spark plug wires and a header gasket?


here ya go.....http://www.summitracing.com/search?keyword=super sucker&dds=1


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## Chris-Austria (Dec 23, 2010)

Thank you!
Will I have to change the Jets if I use this spacer?
And won't the plastic ones be a better heat insulation than aluminium? Would you choose plastic or aluminium for my car?


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## ALKYGTO (Mar 29, 2010)

Plastic. It will insulate the carburetor from engine heat better than the aluminum.

Only way to tell if any changes are needed would be to install and checkon the dyno with an O2 sensor or good old fashioned butt dyno and traditional tuning methods like reading the plugs. I wouldn't say big changes (if any) would be needed.

Another way to check if an individual cylinder is rich or lean is to use a digital infra-red thermometer on the header tubes right at the head. They can be had relatively cheaply.


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## Chris-Austria (Dec 23, 2010)

Okay sounds good. If any change in jetting would be necessary, it would be to a little bigger jet I guess? I also read that the 4-hole spacers are good for dual plane intakes like mine, better than a open spacer and that it will require less change in jet size.
I'll order this one: http://www.summitracing.com/parts/qft-300-4150-1#

I guess I'll need some larger bolts? They include gaskets but no mounting hardware.. I searched for some bolts from Quick Fuel but cannot find them


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## ALKYGTO (Mar 29, 2010)

I prefer studs myself, you can buy some threaded rod and make them the proper length yourself.


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## Chris-Austria (Dec 23, 2010)

Thanks. I found some studs at Summit and measured the "stock" ones.. I think 2.7 to 3" will be good for the studs with spacer.


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