Engine tuning

I recently got my 400 in my '69 Goat running again.  I am working on fine tuning the engine.  It runs pretty well and smooth, but is still not perfect.  It's got a brand new Holley 650 spreadbore carb.  I can't get my vacuum gauge needle to stop rapidly vibrating.  Also, my fuel pressure gauge is vibrating too, if that is related.  It seems to run better at idle, and the needle vibrates less with the mixture screws only about 1 turn out.  Much farther in or out with the mixture screws and the needle jumps way up and down and violently vibrates.  Any ideas?  
1969 GTO, YS code 400, 350hp/445 ft lbs of torque (stock specs), LT headers, H-pipe, 750 Holley 4160, Ignitor II ignition.  Complete Painless wiring.

Sound like one or more of the valves is back firing slightly as known as excessive reversion. This can be due to improper valve lash, something stuck on a valve seat, or not enough timing. Or if your idle mixture is way off causing an incomplete burn which will also cause excessive reversion at idle.

What is timing at idle? Pontiacs like 14 - 16 deg initial. Then reset your valve lash. Then check how much vacuum are you making at idle in gear. Have you changed the power valves according to idle vacuum? Once you do, then you can start tuning the idle mixture. If you are above 2500ft then you should drill out the idle air bleeds .003 for every 2500ft you live at. You then start with 3/4 turn out and adjust the mixture to make the most amount of vacuum and stop.  

I had the heads completely rebuilt at a reputable machine shop.  I also adjusted the valve lash with new self-locking rocker nuts.  Perhaps I should set the initial timing at 14-16* and then go back and adjust the lash again, and then adjust idle A/F mixture?

I am not familiar with changing the power valves.  I am located in Germantown MD, which I assume is not a very high altitude.

Also, the timing is only dialed in by ear.  And when I pulled the plugs they were all black probably from running rich and incorrect timing.  But, 2 of the plugs, number 7 and 6 were still okay and not fouled..

Thanks for the help  
1969 GTO, YS code 400, 350hp/445 ft lbs of torque (stock specs), LT headers, H-pipe, 750 Holley 4160, Ignitor II ignition.  Complete Painless wiring.

By ear(timing) is a crap shoot which among other things has fouled the plugs
flynryan has the correct procedure listed above  

I drove the car home from Frederick to Germantown today.  It's about 25 miles.  The car ran okay.  About 3/4 of the way the temp. rose to around 220* and the oil pressure dropped off to about 20psi cruising and 0-10psi at idle.  I stopped, let it cool off, and then drove it the rest of the way home.  Once I parked I noticed a puddle of fuel under the right rear tire.  I looked underneath and found a fuel hose kinked and cracked.  It was dripping fuel badly.  
1969 GTO, YS code 400, 350hp/445 ft lbs of torque (stock specs), LT headers, H-pipe, 750 Holley 4160, Ignitor II ignition.  Complete Painless wiring.

What are the rod and main bearing clearances on the 400.  
professional hi-performance engine builder

Horsepower sells engines and torque wins races

I have no idea.  My Dad bought the car in CA about 17 years ago.  It still has the same engine with no rebuilds.  I think the problem was that I used nylon tubing for my mechanical gauge.  I found that it was leaking at the fitting at the oil filter.  I replaced the nylon with copper tubing and it is not leaking now, and when I drove the car it didn't go under 20psi oil pressure.  
1969 GTO, YS code 400, 350hp/445 ft lbs of torque (stock specs), LT headers, H-pipe, 750 Holley 4160, Ignitor II ignition.  Complete Painless wiring.

20 psi at what RPM.  
professional hi-performance engine builder

Horsepower sells engines and torque wins races

It's hard to say what rpms since I currently do not have a tach hooked up.  But, basically, when the engine was hot, at idle, or slow decel, oil pressure would be around 0-10 psi, respectively.  I think the engine was getting too hot at around 210-220*, and the old nylon tubing was leaking, both causing the low oil pressure gauge reading.  
1969 GTO, YS code 400, 350hp/445 ft lbs of torque (stock specs), LT headers, H-pipe, 750 Holley 4160, Ignitor II ignition.  Complete Painless wiring.

Someone told me that the rebuilt heads with the fresh valve springs and guides probably just need to be broken in.  He said after I drive the car awhile and bring it through a few heat cycles I should begin to see a steady vacuum gauge needle.  Does this sound accurate or possible?  
1969 GTO, YS code 400, 350hp/445 ft lbs of torque (stock specs), LT headers, H-pipe, 750 Holley 4160, Ignitor II ignition.  Complete Painless wiring.

Put a timing light on it and set it at 16 degrees. Then adjust your advance and set it at about 34-36deg. at 2500rpm. Always set the timing before addressing the carb. If your' carb is newer than 1992 , it will have a pwr. valve protection system. If you screw the air/fuel mixture screws all the way in and the motor quits, then it is not your' pwr. valve.Also try ahotter plug, ac delco r43. Do you have a good ignition system? Oh yeh , check your pwr valve. Your' pwr valve should be half of your vac. at idle. First check your accelerator pump diaphram. It may have a hole in it. If you are pulling a low vac. reading at idle; well that would determine what size cam you have. The bigger the cam the less vac. at idle you will have. Go to holley videos and you will learn alot. I never asked if you had a manual trans or auto. Your reading will differ depending on what you are running. Also check the simple stuff first, do you have any vac. leaks? Check all intake manifold bolts for tightness and also make sure your' carb is tightly secure. But do not over tighten the carb bolts as it could cause a vac. leak due to plate warpage. Man, I understand your frustration. Do your' research, listen to these guys on this site; they have helped me a great deal. Good Luck  

See if you can get your hands on a timing light that displays the rpms as well. If you don't get the timing right , well your' tuning will be based on your ear and a crap shoot. You stated that you didn't have an rpm guage. What kind of carb and trans do you have? Have you checked your comp. ratio.? Youll figure it out. Have confidence and don't be afraid to jump in there. Don't do it blindly, read, use the internet. It is trial and error , but when you get the combo dialed in , it will be so worth it . Dave  

An accurate tach is really essential. The needle broke off my Trans Am stock tach and I hooked up a cheap one from Auto Zone on my dash and it's right on. As far as timing the distributer by ear, it can easily fool you - it can be so far off in the wrong direction that every other adjustment you make will be meaningless. I thought I had my 400 running good until I took it to my buddies at a local speed shop one night and they swarmed all over it. The first thing I noticed was that it began to sound like a steam locomotive. When I drove it home it would barely stay on the road. I had everything so far off and didn't even know the potential I was missing.
Like Dave says, when it's all dialed in right you will have a monster.
Brazil