Engine has mild cam, headers, Petronix distributor, Edlebrock perfomer intake, and Holley 600. I had this problem before i had the heads rebuilt with the above listed items. Never had any problems with stock 2 barrell set up other than it could not get out of its on way. Everything on the top end is new on this engine. I can not seem to get this engine to run without the timing set around 18, with some limiters in the distributor the total advance is 30 around 3K RPM. My problem is a bog taking off and back firing through carb if i set the inital timing any lower than 18. If i keep advancing the distributor the problem will go away but then i think i have way too much timing. Any advice. Every time i take the plugs out and look them over they are as clean as new as if it is way lean or running too hot. Tonight it was not really dark but as i was running the engine up i noticed the headers starting to glow red, i do not think i have ever noticed this before. I was not running that fast either, half throttle. My compression readings are anywhere from 110-120.

Something else that has me stumped, with the timing set low, off idle trying to speed up, i can tell engine is stumbling by the sound and shake of engine then i notice smoke coming up from back of motor, the smell is rich condition not oil burning, i can not find where this smoke is coming out the engine, my headers are sealed for the most part, and the exhaust is ran out to the back of truck.

 

Something else i just thought of, i have my plug wires tye wrapped together leaving the distributor going to each bank of the engine, they are MSD type wires and new, by them being grouped together is there a possiblity of any cross firing?

 

Is your vacuum advance sourcing ported or manifold vacuum?

 

Did you have the distributor out at any point? Maybe installed one tooth off?

 

Vacum advance is ported from carb. Distributor has been out many times, if it was a tooth off it would be corrected when the distributor was turned to adjust timing.

 

What happens if you put a vacuum gauge on it? What does the needle do? This is probably the most useful tool at this point.

 

I have a guage on it, vacum is anywhere from 8 to 12 at idle. Have not watched it when speeding up engine.

 

Are you setting the timing with the vacuum advance disconnected and plugged?

Josh

 

That vacuum reading is way too low. Since you know you have good compression, start checking for vacuum leaks. The fact that your plugs look lean supports a vacuum leak too.

 

Have you actually verified that your timing marks on the harmonic dampner are correct?

If the dampner has slipped it can make it appear to be way off timing.

 

Yes, damper marks line up for when piston is up. I am thinking I have another intake leak on under side of intake again. If this is the case and I can see where it has pulled oil into intake runner why is this happening?

 

Pulled intake, it was not as obvious the intake was leaking like before when i could see where it was pulling the oil. The drive time between gasket changing was not as long either so it may not have had a chance to pull as much oil and was just pulling air. I am trying different brand of gaskets this time. Why are there two different sizes of intake gaskets for the 390? One is slightly longer in the port area than the other, the width is same. The longer one is what is called for but the shorter one matches the port size better which is the one i have been using. Maybe i am loosing my sealing area at the bottom in the lifter area all this time?

 

Some gasket sets are spec'd for 2.34 x 1.40 ports, other sets are spec'd for 2.10 x 1.40 ports.

Which gaskets are you running...Fel-Pro, Mr. Gasket, Victor-Reinz, something other?

 

Have been using felpro. Trying victor this time.

 

Victor-Reinz would be my recommendation as well, they seal much better than Fel-pro imo, Carquest still stocks the Victor line, i prefer the "Nitroseal", here's the part #'s....

Low riser #95158SG
Medium riser #95159SG
High riser #95009SG