# chasing engine problems



## [email protected] (Apr 13, 2009)

I have a 66 GTO. It's nearing the end of a 10 year restoration. The engine is a 400 out of a 68 GTO and I had it freshly rebuilt by an engine shop. Unfortunately that engine shop retired before I ever got a chance to start the car and now I can't get it to run right. I've tinkered with it quite a bit, had a mechanic friend look at it who is pretty "old school" with carbs, and been on various tech support lines for advice. 

The engine has ram air 3 heads on it running about 10.5:1 compression. The cam has quite a bit of overlap to allow it to run on pump gas. It starts ok, doesn't like to idle, gets worse as it warms up and eventually dies most of the time. Although sometimes it idles fine even after it warms up but still won't drive. When I drive it around the block it won't go past 10 mph and jump up and down like the firing order is wrong. Pretty much everything on the engine is new, including the carb. The carb is a holley street avenger 570. It's a little small for the engine but holley tech support and myself don't think that would cause idle problems

Things I've tried with no change:

-Changing the carb to a bigger edelbrock
-check the vaccuum. 9" steady which seems low to me but my research suggest that is normal for the engine specs it has
-Changing the power valve on the holley to match the vaccuum
-trying two different distributors
-putting an MSD box on it and taking it back off (when I changed to a petronix distributor)
-checking for leaks on the intake, despite not finding any changing the gasket anyway
-checking the firing order a dozen times over
-trying several different timing positions including locking it out
-checking for spark with a spark gauge
-running it on 100 octane
-taking compression 170+ in all cylinders
-check the ignition timing timing

Next things I need to try:
-putting fresh gas in it (gas isn't that old so I don't suspect this but the tank could have been contaminated.) 
-swapping out the stock exhaust manifold for headers. I wouldn't think it would make a difference at idle but who knows
-swapping heads
-swapping cams
-double checking my valve springs to see if they go with the cam and head. 

today I thought I reach a revelation and thought the engine builder might have swapped in one of those 4/7 cams where they swap the firing order but my paperwork on the cam says otherwise and I don't think they make them for the pontiac anyway. Any idea what I might be forgetting?


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## geeteeohguy (Feb 2, 2008)

To me, it sounds severely retarded....either base timing, cam timing, or both. I would verify the mechanical base timing of the engine and the positioning of the timing gears. Don't waste time with headers, and swapping a bunch of parts just yet. You need to do one thing at a time and go from there. Start with verifying your cam position, and then verify that #1 cylinder is at TDC and check your timing pointer and distributor rotor location. Lots of info on this if you dig around a bit. My gut tells me your cam timing is probably off.....it happens....BTDT. Keep in mind, also that a 'large' cam with a lot of overlap doesn't compensate for being able to 'get away' with high compression on pump gas. Sure, you'll get less cylinder pressure at low speeds, but you'll end up paying the piper when the engine 'comes on the cam' at increased RPM and fills those cylinders as designed. With 10.5 CR and iron heads, you will need to run higher octane fuel than is available at the pump.


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## [email protected] (Apr 13, 2009)

Thanks for the reply. At one point I had to take the timing cover off. It did reveal the timing chain at zero degrees with on the power stroke for #1 the marks on the timing gears were pointing away from each other rather than lined up. I was convinced this was the problem and I had the car firing on the wrong cycle. I thought it might be running poorly because it was firing on the exhaust stroke. So I turned the timing back 180 degrees thinking this was the issue. The car didn't start but did in fact make a loud boom under the hood.......... Afterwards I checked my work by taking the valve covers off and seeing what valves opened when and I was right the first time. The engine builder just had the timing marks pointed away from each other at 0 degrees. I assumed he put the timing gear on the cam 180 degrees backwards lined up the marks at TDC for the exhaust stroke and didn't verify they lined up at the power stroke instead.......... But if he messed that up maybe he got the cam degrees off as well and instead of being 180 degrees off he's an extra tooth or two off and is actually 185 or 190 degrees off. 

As for the overlap. I talked to the tech support at comp cams. They told me that cam is specifically designed to bleed off heat and pressure in the cylinders to prevent detonation on pump gas. Are you saying this is contrary to that advice?


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## BearGFR (Aug 25, 2008)

+1 on the timing, especially if it's not running the stock points distributor. Take that factory initial timing spec and throw it out the window - it no longer applies. If you don't have a timing light capable of measuring total advance, get one (or put an accurate timing tape on the balancer). Also since there's a lot about the engine that's in question it would pay you to verify that TDC on the timing marks is actually real TDC. Worn factory balancers can slip, and aftermarket ones are sometimes not marked correctly. Verifying the marks can be done without tearing the engine down or removing the heads, but you have to be very careful how you do it. You can use a "spark plug hole" piston stop like one of these 
Spark Plug Hole Piston Stop 
but don't even _THINK_ about installing it before you remove both rocker arms on the cylinder so that the valves cannot move, otherwise you run the risk of bending a valve as it contacts the stop as you're turning the engine over. If your heads have the Pontiac factory rockers and studs, reinstalling the rockers is simple - just reinstall and torque them down to spec (the factory system isn't adjustable). If you happen to have an adjustable system with poly-lock rocker nuts (the ones that have hex socket set screws in the middle) then hold the outer nut with a wrench, back off the set screw, and then carefully count the turns needed to back off the nut so that you'll be able to reinstall at exactly the same spot before re-tightening the set screw. 

The best way to install the stop is to _REMOVE BOTH ROCKERS_ (can't emphasize that enough) on #1 cylinder then turn the engine over "forward" by hand (use a big socket and lots of leverage on the balancer bolt) until the timing mark on the balancer indicates TDC, then keep going until it's a couple inches PAST TDC. 
Thread the stop into the spark plug hole, screw down the adjuster until you feel it touch the piston, then back if off a few turns. Now with the stop installed, carefully turn the crank in "reverse" direction with a wrench on the balancer bolt until you feel the stop, make a chalk mark on the balancer that lines up with the TDC mark on the timing cover. Don't go "he man" on it, you're just trying to find where the stop is. Next turn the crank in the 'forward" direction until you feel the stop again - make another chalk mark. TDC will be exactly halfway between the two marks. If this isn't in the same spot as the mark on your balancer, then either it's marked incorrectly or it has slipped on you and should be replaced. 

Here's an example of a timing light that can measure total advance:
Bosch Advance timing light

Process:
After you've verified TDC is TDC, disconnect and plug the hose for the vacuum advance canister, loosen the distributor hold down bolt enough so that you can turn it but still somewhat tight so that it won't turn by itself.
Start the engine, have a helper hold and maintain a steady 3300 rpm. Using the advance feature of the light, set the timing to 34 degrees. Shut the car off, lock down the distributor, then repeat the process just to make sure nothing moved on you (if it did, fix it). Now, start it and let it idle --- still with the vacuum line disconnected and plugged. Use the light to find out what the initial timing is and make a note of it - this you're doing just so you will be able to return to this setting without having to go back through setting it at RPM.

Reconnect the vacuum line now and drive the car - let us know how it does.

Bear


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## PontiacJim (Dec 29, 2012)

I agree with geeteeohguy & BearGFR that is does sound like a timing issue. However, my experience with a really retarded distributor timing is that the engine will heat up really fast on you - you can watch your temperature gauge climb. You did not mention that you experienced this problem? 

I know you have double & triple checked everything, but lets run through some basics just in case.

First, have you observed the rocker arms with engine running to make sure nothing obvious like rounded/worn cam lobe? No rockers have fallen off or gone sideways and bent a pushrod?

Roller cam or flat tappet hydraulic cam? Assume flat tappet? 

Firing Order - Counter Clockwise on a Pontiac. 1-8-4-3-6-5-7-2

#1 spark plug at the distributor cap should be at the 5 o'clock position as you look at the distributor from the front of the engine - or pretty close to it.

What do your plugs look like when you pull them? Wet, fouled, metal flecs, etc.? Correct heat range plug?

Do you have a new harmonic balancer? The outer ring is bonded to the inner section and on an older balancer, it is not uncommon for the rubber to deteriorate and the outer ring to slip - giving you an incorrect timing reading. And, make sure that harmonic balancer bolt gets torqued to 160 foot pounds or the collar that goes onto the crank can crack/break.

Does the engine have the 8-bolt water pump or later 11 bolt pump. Each has the different timing cover and needs the matching harmonic balancer. There are 2 sizes of balancers with the 8-bolt water pump cover using the smaller diameter. If it was swapped over to the 11-bolt cover and the smaller 8-bolt balancer was kept, timing marks on the balancer will not match correctly the timing scale on the timing cover.

Noted you have done a Pertonix Conversion. Needs to have the correct air gap. Needs to have the correct matching coil, and you need 12 volts to it. The 1966 uses a resistance wire for points and drops the voltage to 9 volts while engine is running. If the key has been left on for any long period, I have read that this is one of the biggest reasons why the Pertronix conversions failed on their earlier units. They have supposedly corrected this on later versions.

Stock manifolds - does the manifold still have the "butterfly valve" with bi-metal spring? These were used to send hot exhaust gasses through the intake manifold exhaust crossover for faster warm-ups in cold weather. As the engine got to temp, the bi-metal spring opened up the valve and exhaust gasses exited as usual. If it is frozen shut, it'll cause problems and choke the engine. Exhaust pipes not damaged or plugged along its length?

What intake? Noted the Holley and swap to the Edelbrock (AFB?). If using a stock Q-jet intake manifold with these carbs, you would need an adapter. It has happened where the adapter was hanging just enough over the edge, but not really visible, to cause a vacuum leak because the gasket did not seal as it should have. The best intake is a dual plane and not a single plane intake. The single plane intake, if used, can be problematic at lower RPM's.

Have you checked fuel pressure at the carb? Could be a fuel pump, air entering the system via a split or bad rubber line, the sock on the tank's pick-up tube plugged up, wrong style of gas cap (non-vented vs vented) not allowing the gas to be drawn from the tank, kinked line, plugged fuel filter.

9" of vacuum is very low and indicates a fairly radical cam, but indeed may be the overlap in the cam. The factory cylinder pressure for the 1968 GTO 400 with 10.75 compression is 185-210 PSI @ 155-165 RPM's. Overlap on the "068" GTO cam is 63 degrees. I know that your cam has more overlap, but that cam will be poor down in the lower RPM range and won't perform at its best until you hit mid-upper RPM's. So if you have a stock torque converter or running 3.55 gears or lower - that engine will be bucking. With a radical cam more on the side of a race cam, you need a high stall converter and most likely 3.90 gearing or better to work with the cam.

PVC valve hooked up and working?

If you have power brakes, they may not work so well with 9" of vacuum. If you have power brakes - I would also check the check valve that comes off the hose from the carb/manifold that goes to the master cylinder brake booster just to make sure it is not bad and sucking air. This has happened to another member here and was causing problem. Valve appeared good and seemed to work, but it was worn out and not working as it should.

Lift on the valves? Any chance they are hitting the piston tops? Springs matched to the cam so the valves are not bouncing? 

You did not mention if you have a stock valve train, ie torqued the rocker arm nuts down to 20 ft pounds, or have the adjustable poly-locks. It is possible that your valve are adjusted too tight in either case and being held open just enough to be a problem. Not saying this is the case as all your cylinder pressures seem consistent, but could be something to check.

If all this checks out, then I am onboard with a timing issue - whether cam or ignition.

Keep us posted and we will get it solved. :thumbsup:


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## BearGFR (Aug 25, 2008)

9" of vacuum is SUPER low unless you're running a pretty nasty cam. 

What are the specs on your cam? (Duration at .050 tappet lift, lobe separation angle, etc) and what kind of cam is it? Hydraulic, solid, flat, or mechanical?

As a point of reference, the cam in my 69 *is* a reasonably nasty solid roller, and my car makes 10" of vacuum idling in gear at about 850 RPM, 14-15" idling in neutral at 1100 rpm. 

Bear


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## geeteeohguy (Feb 2, 2008)

[email protected] said:


> Thanks for the reply. At one point I had to take the timing cover off. It did reveal the timing chain at zero degrees with on the power stroke for #1 the marks on the timing gears were pointing away from each other rather than lined up. I was convinced this was the problem and I had the car firing on the wrong cycle. I thought it might be running poorly because it was firing on the exhaust stroke. So I turned the timing back 180 degrees thinking this was the issue. The car didn't start but did in fact make a loud boom under the hood.......... Afterwards I checked my work by taking the valve covers off and seeing what valves opened when and I was right the first time. The engine builder just had the timing marks pointed away from each other at 0 degrees. I assumed he put the timing gear on the cam 180 degrees backwards lined up the marks at TDC for the exhaust stroke and didn't verify they lined up at the power stroke instead.......... But if he messed that up maybe he got the cam degrees off as well and instead of being 180 degrees off he's an extra tooth or two off and is actually 185 or 190 degrees off.
> 
> As for the overlap. I talked to the tech support at comp cams. They told me that cam is specifically designed to bleed off heat and pressure in the cylinders to prevent detonation on pump gas. Are you saying this is contrary to that advice?


Yes and no. Cams with a lot of overlap bleed off cylinder pressure at lower rpms. This can allow you to 'get away' with high compression on less octane at cruising speeds and lower. But when you stand on the throttle, that cam will do what it was designed to do: fill up the cylinders quickly to make horsepower. If it didn't do that, your engine would be a real slug. Running any iron head that gives you a compression ratio of over 9.5: 1 with a Pontiac engine will generally need 95-100 octane fuel to run without detonation. I agree that 9" of manifold vacuum is too low for anything but a race-only engine, if caused by camshaft profile.


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## BearGFR (Aug 25, 2008)

[email protected] said:


> Thanks for the reply. At one point I had to take the timing cover off. It did reveal the timing chain at zero degrees with on the power stroke for [URL=https://www.gtoforum.com/usertag.php?do=list&action=hash&hash=1]#1 [/URL] the marks on the timing gears were pointing away from each other rather than lined up. I was convinced this was the problem and I had the car firing on the wrong cycle. I thought it might be running poorly because it was firing on the exhaust stroke. So I turned the timing back 180 degrees thinking this was the issue. The car didn't start but did in fact make a loud boom under the hood.......... Afterwards I checked my work by taking the valve covers off and seeing what valves opened when and I was right the first time. The engine builder just had the timing marks pointed away from each other at 0 degrees. I assumed he put the timing gear on the cam 180 degrees backwards lined up the marks at TDC for the exhaust stroke and didn't verify they lined up at the power stroke instead.......... But if he messed that up maybe he got the cam degrees off as well and instead of being 180 degrees off he's an extra tooth or two off and is actually 185 or 190 degrees off.
> 
> As for the overlap. I talked to the tech support at comp cams. They told me that cam is specifically designed to bleed off heat and pressure in the cylinders to prevent detonation on pump gas. Are you saying this is contrary to that advice?


You were actually right both times. Think about it - the cam gear turns exactly once for every two revolutions of the crank, so if you line the gears up "mark to mark", or both of them at 12 oclock - it's exactly the same thing. Install the gears "mark to mark", then turn the crank exactly one revolution and look - now they'll be both at 12oclock. So, installing the gears either way is correct. What matters is making sure that the distributor rotor points to #1 cylinder terminal at the same time that cylinder #1 is at TDC on the compression stroke, not TDC on the exhaust stroke. 

Cam timing/valve timing which is what you're dealing with that involves the timing chain and gears, is separate from ignition timing - which is what we suspect is causing your problems.

Bear


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## [email protected] (Apr 13, 2009)

Thanks for all the advice. Lots of questions asked and things brought up I never thought of. I have the cam specs at home i can post tomorrow but don't know off hand. Harmonic balancer is something I didn't think of. Although I would think the timing would be moving around quite a bit if that was the case but it stays pretty consistent and verified it is at TDC to line up with the marks. I've also tried many different timing settings from many different recommendations and nothing seems to make a difference for running better or worse. I have a good timing light and I feel like I've ruled out ignition timing pretty well. The spark plugs look pretty normal but I haven't run it enough to indicate much just yet.

Valve timing might be a different story though. I'm starting to think the engine builder got the cam off by a few marks. I'm also thinking the cam is too hot for the car. I might end up swapping the heads and putting in a more mild cam. I really don't want to run race gas or even premium for that matter, top end power is completely useless to me, I want a cruiser not a racecar, and it's a convertible that is WAY too loud anyway. I would rather have something I can put 87 octane in and cruise around and get decent mileage (at least for an old muscle car not by toyota prius standards) than a fast car. It's a 4 speed convertible going fast is not what I want this car to be all about. I told my engine builder that but I think he heard me say, "build me a nascar engine." I'm also wondering if the 9" of vacuum isn't enough to make the venturi on the carb work right. Holley tech support said it would be ok but they also didn't seem to sure of themselves. 

I know where I can pick up some machined iron heads for pretty cheap. My ram air 3 heads I could probably sell and that would be a wash. I might even consider aluminum heads. Or keep it simple and run a thicker gasket. Has anybody ever done this to lower compression? I can't seem to get a consensus if this is a good or bad idea. I also like the idea of a roller cam but not sure I want to spend that much converting it.


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## BearGFR (Aug 25, 2008)

Running thick head gaskets to deal with a compression problem is a bad idea, do not do it. The reason is because that will kill the quench characteristics in your combustion chambers. You want the tops of the pistons to be coming within about .040-.050 of an inch to the tops of the cylinder heads because this helps to promote turbulence in the chambers. Turbulence in the chambers is good for helping you avoid problems of detonation. If you don't have good quench the engine will actually be more prone to detonate even though compression may be lower. Fat gaskets are a solution of "last resort" only after you've done everything else to address the problem, including changing pistons. 

Also just because your timing mark isn't jumping around tells you absolutely nothing about whether or not the mark is correct. All that means is that you don't have a lot of excessive slack in your distributor drive gear or timing chain, and also that the outer ring of the balancer isn't loose and moving. It's quite possible for the marks to be off and still be steady in the light. You won't know until you actually verify it. The only way you're ever going to find out what this engine is actually doing is to start verifying and checking things. Or you can keep randomly changing parts, spending money, and just hoping that you happen to get lucky and stumble over it. It's your choice.

Also, when you set your timing are you doing it with the vacuum line to the advance mechanism disconnected and plugged? If not then that's a problem.

I just reread your original post and paid attention to what you said you've tried and what you didn't mention. One thing jumped out at me having to do with carburetion (yes, that 570 Holley is WAY too small) but I really want to know what your cam specs are before chasing it too far. I'm guessing that you're having to open the idle speed screw in quite a bit to get it to idle, so much so that it's actually idling on the transfer slots and not on the idle mixture screws. Here's a quick way to tell: turn your mixture screws all the way in just so you determine their current settings, then reset them back to where they are now. Start the engine and let it warm up some. Start turning the mixture screws in. Can you kill the engine just by turning those screws or do they seem to have little to no effect? If they don't do much of anything to how the engine runs, then you're running on the transfer slots. This is a problem that needs to be addressed before you try much of anything else.

I also just reread your post about when you checked the timing marks yourself with the timing cover off. You said the marks were pointed "away from each other" --- what exactly did you mean by that? If the mark on the crank sprocket is at 6'oclock and the mark on the cam gear is either at 12 o'clock or at 6'oclock, then that's definitely wrong --- but I'm not sure the engine would run at all with it like that. If things are correct, then when the crank sprocket is at 12'oclock then the cam sprocket should be at either 6'oclock (pointed directly at the crank mark) or also at 12'oclock. If you're not positive about the orientation, then it would be a good idea to pull the cover again and make certain. With the crank sprocket at 12'oclock, you should be able to line a straight edge up with the center of the balancer bolt hole, the mark on the crank sprocket, the mark on the cam sprocket (either 6'oclock or 12'oclock - doesn't matter which), and the center of the cam bolt hole.


Bear


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## [email protected] (Apr 13, 2009)

It's a little hard to tell the story of everything I've done because this would be a much longer thread. I agree it's a lot better to check things than blindly change parts hoping it will fix the problem. It's getting to the point where I'm running out of things to just check and changing something makes more sense because even if the car runs perfectly I still don't like how the engine was build: too loud, too powerful, too high of octane fuel, ect. 

The timing in the same spot I meant to be verifying the ring on the harmonic balancer isn't moving around. I have checked the ignition timing pretty extensively. TDC lines up perfectly with the timing mark, the car runs the best at what my engine builder told me to advance it. It runs better (but still bad) and gives the most vacuum and I believe it was 8-10 degrees advance. I've tried a few different things to vary how much total advance but that's more of a long term thing. 

I checked the torque specs on the rockers but checking the valve timing is something I haven't done and don't really have the equipment for it. Other than shooting from the hip and figuring out the valves are opening about the right time based on where the pistons are. I think that will be the next thing I investigate. The heads were machined along with a full rebuild on the engine. Basically ever component on the engines has zero miles on it. 

Here's the cam I have: 51-224-4 - Xtreme Energy? Hydraulic Flat Tappet Camshafts


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## PontiacJim (Dec 29, 2012)

IMPORTANT NOTE: Often overlooked is the altitude at which you call home. If you live in Denver, CO vs Miami, FL, altitudes are quite different. At higher altitudes, the air is "thinner" so you build your engine WITH higher compression to get a tighter squeeze on the air/fuel mixture. This same high compression at lower altitudes would cause your engine to need racing gas to run properly with detonation or knocking. So a 10.75 or 11.0 compression engine in Denver would probably work fine on pump gas - but never work in Miami. So just wanted to throw that out there.

I had that cam in my last 8.2 compression 1973 400 build. That cam only has 60 degrees of overlap - not much and certainly not enough to "bleed off" compression. The 110 Lobe Separation Angle (LSA) is not a good choice at all for a 10.75 compression engine. The 110 LSA will increase dynamic compression, ie it raises cylinder pressure which you DON't want - you want to lower it. This is why these cams actually work best in a low compression engine because they build MORE cylinder pressure.

That said, my comments are based on lower altitudes and not the "nose bleed" sections of the US.

A better cam, as an example, would be a wider LSA of let's say 114-116 degrees and an overlap of around 80 degrees. This would be a cam that would "bleed off" cylinder pressures at the lower RPM's. 

The factory GTO "068" cam had 63 degrees of overlap, the hotter "744" Ram Air cam had 76 degrees of overlap, and the infamous Ram Air IV cam had 87 degrees of overlap - just to give you examples. 

You should have way more vacuum than 9" with that cam, so you have a serious problem going on. Personally, I would start from scratch and partially disassemble the engine. Do you know for a fact that the engine builder used stock pistons and did not go with a dished piston to lower compression? This would explain the 170 PSI cylinder pressures - and not a cam with a lot of overlap.

You really need to know what your actual compression(called "static compression") is in order to match a cam to the engine. You will need to know what the chamber cc's of the head are, head gasket thickness, how far down in the cylinder bore the top of the piston is, and what the total cc's are in the valve reliefs (or dish) found on the top of the piston. This will provide what the true compression ratio of your engine is. Here is what you need: Compression Ratio Calculator - Wallace Racing

Then once known, select a cam that matches the compression ratio. You will at that point degree that cam to ensure it matches the cam manufacturer's spec and is installed per the manufacturer's specs. Cam selection can be used to somewhat lower cylinder pressure to give you a lower "Dynamic Compression" at the engine's lower RPM range. Found here: Wallace Racing: Dynamic Compression Ratio Calculator 

If you had the heads milled, it is also possible the pushrods are of the wrong length and now too long. It is possible they are hanging open the valves. The recent and ongoing post "Need pushrod length" will give you some great info on how to determine this.

So I do not think at this time with the info you have supplied that you are going to solve your problem as it is without more detailed info about your engine. Guessing here won't work and you could damage the engine. You have waited this long, so I would not take any chances. It may set you back a little on time, and a few extra dollars, but it will be worth it. Many here who can help you through this. :thumbsup:


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## BearGFR (Aug 25, 2008)

That's not a big cam at all, not by any stretch of the imagination. It should be making way more vacuum than that. Something else is wrong. 

By way of comparison, my previous build had a "bigger" cam - 236/242 @ .050 and it made an easy 14" of idle vacuum. My current one is even bigger: 251/257 @ . 050 and it makes 10" at idle. The one you have should be making 15-16+, easy. 

Are you setting ignition timing with vacuum disconnected and plugged?
Are your idle mixture screws effective?
Have you verified that when the balancer marks indicate TDC, it really is TDC?

Bear


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## dd68gto (Nov 14, 2012)

[email protected] said:


> It's a little hard to tell the story of everything I've done because this would be a much longer thread. I agree it's a lot better to check things than blindly change parts hoping it will fix the problem. It's getting to the point where I'm running out of things to just check and changing something makes more sense because even if the car runs perfectly I still don't like how the engine was build: too loud, too powerful, too high of octane fuel, ect.
> 
> The timing in the same spot I meant to be verifying the ring on the harmonic balancer isn't moving around. I have checked the ignition timing pretty extensively. TDC lines up perfectly with the timing mark, the car runs the best at what my engine builder told me to advance it. It runs better (but still bad) and gives the most vacuum and I believe it was 8-10 degrees advance. I've tried a few different things to vary how much total advance but that's more of a long term thing.
> 
> ...


Just s little advice after reading . If you follow Bears advice you will find out where you stand. To many think by adding their two cents they are helping but they are just confusing you. That is huge CR for iron heads but first is to make sure you are on tdc and get timing correct . Just to add small carb will not cause your issues. Maybe loss of power at high rpm. . Also elevation is not your problem unless you are on Mount Everest . Listen to Bear . . Best luck Doug


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## [email protected] (Apr 13, 2009)

PontiacJim said:


> IMPORTANT NOTE: Often overlooked is the altitude at which you call home. If you live in Denver, CO vs Miami, FL, altitudes are quite different. At higher altitudes, the air is "thinner" so you build your engine WITH higher compression to get a tighter squeeze on the air/fuel mixture. This same high compression at lower altitudes would cause your engine to need racing gas to run properly with detonation or knocking. So a 10.75 or 11.0 compression engine in Denver would probably work fine on pump gas - but never work in Miami. So just wanted to throw that out there.
> 
> I had that cam in my last 8.2 compression 1973 400 build. That cam only has 60 degrees of overlap - not much and certainly not enough to "bleed off" compression. The 110 Lobe Separation Angle (LSA) is not a good choice at all for a 10.75 compression engine. The 110 LSA will increase dynamic compression, ie it raises cylinder pressure which you DON't want - you want to lower it. This is why these cams actually work best in a low compression engine because they build MORE cylinder pressure.
> 
> ...


Ya I guess I should have started this thread out with all the info I could. The builder said the engine had between 10.25 and 10.5 compression. The pistons are aftermarket but I don't think they are dished. I live in Portland Oregon so it's about 500 foot elevation. Other than that most of the possible problems with too high of compression I eliminated by putting 100 octane leaded fuel in it (the third fuel I tried with no difference in how it ran). I know a lot of people have mentioned ignition timing several times but I'm pretty certain I got this correct. Push rod length is a good thought too. Although I could turn all the push rods with closed valves with my finger w and no slack in them. 

[/QUOTE] Are you setting ignition timing with vacuum disconnected and plugged?
Are your idle mixture screws effective?
Have you verified that when the balancer marks indicate TDC, it really is TDC? [/QUOTE]

1) Yes I did
2) Tried setting mix srews with vacuum gauge on two different carbs follow both setting instructions then had a former mechanic with a lot of experience tuning carbs take a crack at both of them. Still couldn't get it right. 
3) Yes timing marks match TDC.


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## BearGFR (Aug 25, 2008)

[email protected] said:


> 1) Yes I did
> 2) Tried setting mix srews with vacuum gauge on two different carbs follow both setting instructions then had a former mechanic with a lot of experience tuning carbs take a crack at both of them. Still couldn't get it right.
> 3) Yes timing marks match TDC.


1) Good - but realize that especially since I read that you've tried several different ignition systems (MSD and Pertronix I think) - that the initial timing setting doesn't mean squat. The only way to be sure it's close is to set total timing (again, vacuum disconnected and plugged) to 34 degrees at 3300-3500 RPM as a starting point.

2) This is a clear indication that either the engine is idling on the transfer slots, or you have a significant vacuum leak. There's a way to correct the transfer slot problem and restore functionality to your idle screws, but you first have to pick a carb and stick with it. This engine is going to be happiest with at least 750 cfm. (Which, by the way, just happens to be what the original factory QJet was).
What's the lowest RPM you can get it to idle at?

3) Sorry to keep harping on this - maybe it's just me, but I'm not getting the feeling that you understand what I'm talking about. Just because the mark on the balancer points to TDC on the timing cover does not mean that the engine is actually at TDC. That outer ring on the balancer where the mark is can slip on the layer of rubber that bonds it to the inner hub, especially if it has some age on it, causing things to be off. I've also seen brand new, out of the box, aftermarket SFI-rated balancers with TDC markings that were off by 6 degrees or so - such that the actual engine ignition timing was 6 degrees LESS than what was indicated by the balancer marks + timing light. If you're not positive that the marks on the balancer and timing cover are showing you actual engine TDC when they are aligned, then your light could be lying to you without you knowing it.

You mentioned that the engine may .have 10+:1 compression. That can be very risky with iron heads. I recommend that you remove a few spark plugs and examine them very closely with a good magnifying glass to find out if you can detect any shiny metallic specks on them. If so, what you're probably seeing are bits of aluminum from the pistons resulting from detonation - which isn't good. 

Something else you might try: Disconnect every vacuum hose at both the carburetor and the intake manifold and plug/cap the connections. A bad vacuum leak can cause the symptoms you've been describing and they're not always obvious - a leaking diaphragm inside the power brake booster for example. Your engine with that cam ought to be making a lot more than 9" of vacuum. Another trick for finding a leak: use an unlit propane torch to "squirt" propane at various points around the intake with the engine running. If you find a spot where adding propane makes it run better, you've found a leak. This is a good trick because it lets you check underneath the manifold where it's otherwise hard to test. 

Things happen for a reason - something as of yet undiscovered is going on here.

Bear


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## geeteeohguy (Feb 2, 2008)

I'm thinking that the valve timing may be off due to an incorrect timing chain install. That 9" of vacuum has me leaning that way. FWIW...


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## [email protected] (Apr 13, 2009)

BearGFR said:


> 1) Good - but realize that especially since I read that you've tried several different ignition systems (MSD and Pertronix I think) - that the initial timing setting doesn't mean squat. The only way to be sure it's close is to set total timing (again, vacuum disconnected and plugged) to 34 degrees at 3300-3500 RPM as a starting point.
> 
> 2) This is a clear indication that either the engine is idling on the transfer slots, or you have a significant vacuum leak. There's a way to correct the transfer slot problem and restore functionality to your idle screws, but you first have to pick a carb and stick with it. This engine is going to be happiest with at least 750 cfm. (Which, by the way, just happens to be what the original factory QJet was).
> What's the lowest RPM you can get it to idle at?
> ...


I really appreciate taking all this time helping me diagnosis my issue, you and everybody. 

1) I believe I had the initial timing at 8-10 degrees and total to about 36. I've tried so many different things as I was hunting down the issue. The reason I switched distributors is the MSD was a centrifical advance only. I listened to enough people tell me this was a "race only" distributor and my car would not run right with it. Plus I wasn't a big fan of the big red MSD box look on my car. Petronix has centrifugal, vaccuum advance, HEI, and Multi spark all in one distributor. But it didn't change anything when I swapped them. 
2) It's not idling much below about 950. The carb size is 570. Which I realize is too small. Holley tech support said it would be fine for idling but I'd loose power in the top end. The carb is brand new. I also took an edelbrock 750 off my oldsmobile which ran perfectly on the oldsmobile and has a 400 but that didn't change anything. 
3) the reason I don't think it's the harmonic balancer is I checked the timing mark twice with the piston at TDC. And while it was running that mark never moved. I would assume if that balancer ring was slipping the timing mark would keep changing despite what the car is doing. Plus even though it's running bad it's somewhat consistently in what it does. Although sometimes it runs great and continues to run great for 10 mins. Other times it's running bad within 30 seconds. 
4) I never thought of that for checking for aluminum pieces. That's a good thought. I don't really think compression is contributing to my problems at the moment as I'm running 100 octane leaded fuel at the moment. This was after trying 92 and 95 unleaded. I was noticing some detonation with the 92 as it would diesel when it shut down. But the other two fuels are running the same. This is a longer term issue I will want to address further down the road because I have no desire to run a car a can't buy fuel for at the pump. 
5) I didn't do this with propane but I did get a long hose on a can of starting fluid and checked all over with that and got nothing. 

I am starting to think my vaccuum gauge might be off. I bought it brand new and shows 9" with this car but if I put my hand over the carb it feels like it's going to suck my hand into the engine. Currently my number one suspect is the valve timing off. So far all roads lead to this. The only reason I don't want to say this is it because I should exhaust all other possibilities of less labor and cheaper first. Plus it's probably not something I'm going to attempt to tackle. Also the engine builder had 30 years experience. It would seem more likely it would be something I messed up but it also wouldn't be the first time I've had someone with 30 years experience mess something up.


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## BearGFR (Aug 25, 2008)

Gah --- my browser keeps crashing on me on this machine and this time, it "lost" a long reply.

Check out this video - it's a good explanation of the transfer slots and why having too much exposed renders your mixture screws ineffective. Near the end he also provides a solution.






The video is about Holley but the principles apply to all makes of carburetors.

I'd also make sure that vacuum gauge is telling the truth..

Bear


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## dd68gto (Nov 14, 2012)

dd68gto said:


> [email protected] said:
> 
> 
> > It's a little hard to tell the story of everything I've done because this would be a much longer thread. I agree it's a lot better to check things than blindly change parts hoping it will fix the problem. It's getting to the point where I'm running out of things to just check and changing something makes more sense because even if the car runs perfectly I still don't like how the engine was build: too loud, too powerful, too high of octane fuel, ect.
> ...


I hate saying anything here but I had a 65 gto 389 that ran great back around 1995. I like a fool thought I would put some racing gas in. The problem is this high octane gas desolved all the dirt and grime in my fuel tank/ lines and carburetor causing so many issues I can't list, I'm not saying that's your issue but if that car had sat for a while and you added race gas you may have other issues also. Sorry just wanted to add this . Doug


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## BearGFR (Aug 25, 2008)

You know, I think at this point it would be good for you to go ahead and pull the timing cover just to make certain of what you've got in there. That question keeps coming up, and you're not going to know for certain until you look.

Make sure you drain all the coolant first, including the two pipe plugs down low on either side of the block. Otherwise when you pull the cover it's going to dump some coolant into the pan.

Bear


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## Lemans guy (Oct 14, 2014)

Lots of great advice from the gang and all spot on. Let me add a bit to build on it.

Your original post says that you matched a power valve to idle vacumn. Now you may mean lower, but if you made it the same such as 9hg idle and 9.5 or 8.5 power valve you have an extreme rich mixture that will allow the car to start fine,....but once warmed up will run like crap..or like yours.....it will be so rich the plugs will not fire and a constant and multiple cylinder misfire will occur......

The power valve is not involved at idle and only sometimes comes into play when you are on the idle circuit which is usually up to about 2500 rpm.....2000 to 2500 at any rate. So with that and just until you get her running you might want to use a stock 6.5 or 4.5 valve to make sure it is out of the equation. Maybe it is already, just can’t tell from you post.

Secondly it does really sound like your timing is messed up. Since the car starts. Start it up and with vacumn to the distributor plugged see what your timing is.....if it is starting your base timing is within range. You can do like bear said, and also check what the timing is inside the distributor, with an advance timing light you can run it up and see where the timing stops advancing, with that number minus your base timing at least you will see if timing is advancing. 

A Petronix has to have the correct gap, 010 to 060 and they experience problems with the grounds, they must be solid grounds.

A distributor not advancing will make it act this way, however you said you tried two different dizzies and same problem.

The original Ballast wire, I think PJ mentioned...reduces voltage to the distributor, petronix and MSD run best with 12 volts, if your ballast wire is running 6 or 7 volts, when it was designed for 9 And the Petronix wants 12 volts it will run like crap.

Verify the voltage from the ballast wire if not 12 volts it is an easy fix a relay on the firewall, any parts store, will take that and send 12 volts to the coil/Distributor....the relays close at very low voltage and stay closed like even lower...so they are very reliable and Petronix even recommends them.

So if voltage is down start there. 

I would be looking there, timing and mixtures, before I pulled off heads and cam etc.:nerd::nerd:


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