Ok, I bought my long desired 68 camaro a couple of months ago and have been chasing some questionable performance ever since. I'll give you the history of the last few weeks just incase there is anything that helps with the direction of where I'm going.

When I was first able to get it out on the road, there was a hesitation and severe sputter and backfires when reving it. I started with new gas/dry gas, then moved to the timing. I could not get a good reading. I manually confirmed TDC and marked it on the balancer. I replaced the plugs (original Accel 576 for AC Delco 44T) and wires and then checked the plug color. Most seemed to be running lean except for the number one plug which was wet and black. I was going to replace the cap and rotor but then realized that the mechanical advance weights were completely worn out. Ultimately I replaced the entire HEI distributor with a Summit HEI unit to be sure all components were ok.

I ended up replacing the delco plugs for Accel 576s (shorty header plugs) as the others had the wires to close to the wires. I did a compression test on all cylinders and all were north of 150 and consistent between them. Most recently I tested the voltage out of the alternator and to the primary on the HEI. Alternator puts out 14.5 the HEI primary was fluctuating and never above 13.00v. Today I realized the previous owner wired the primary to the original resistance wire so I replaced that and now have a steady 14.3-14.5v at the primary.

Car has continued to run progressively better, but still seems like it is missing. I pulled the number one and three plugs today. Three is a little lean looking and one was black and had oil/carbon deposits all over it. I moved the timing light induction pickup to each spark plug wire one at a time to see if any were missing and they all look ok.

So with good compression, a completely new ignition system, what else might cause a misfire and or one plug to show rich when others are not? Anything else I should be looking at? Sorry so long, but this has been my life for the last 2 months. Thanks in advance.

 

1) Where is your timing set at?
2) What kind of carburetor do you have?
3) Which port on the carb do you have the vacuum advance hooked to?

 

1) Where is your timing set at?
I have moved it around in testing. Currently 34 deg at 3000 rpm.
2) What kind of carburetor do you have?
Edelbrock 1407
3) Which port on the carb do you have the vacuum advance hooked to?
Plugged into the drivers side which should be full manifold vacuum.

Could timing or carb create a situation where only one cylinder is missfiring or running rich? The plug on the number one cylinder is so different than the others. I know the plug must be firing because the timing light is lighting when on that plug wire.

 

1) ok
2) ok
3) Move the vacuum advance hose to the passenger side (ported/timed vacuum), and see what happens. The vacuum advance on our car was already switched over from using (pre-smog era) manifold to ported vacuum. And aftermarket distributors are designed to run on smog era engines, requiring it to be hooked up to ported vacuum. Your distributor's vacuum advance isn't "tuned" to work well on full manifold vacuum, so it's running already at full vacuum advance at idle. Then what's happening is as soon as the throttle blade opens, vacuum drops, and so does your timing advance, giving you a hesitation/stumble.
Is this a new, or newer built engine? Perhaps the rings on the #1 cylinder haven't fully seated yet.

 

Thanks for the suggestions. I havent tried moving the vacuum yet, but I did realize that after all of the initial changes I had made, I had most recently had the base timing set around 12 deg as it didn't want to idle very well when it was advanced much further. Now that I have addressed all of the ignition system issues, I advanced it to 14 and it ran much better. Supposedly, the engine doesn't have that many miles on it since the rebuild so hopefully it is that the rings are not seated yet on the number one cylinder.

I'm hopeful that from here it will just be minor timing and carb adjustments. Thanks again.