Running Rich

[dbr25]

I just rebuilt a 350 for a guy and the thing runs pretty good cold but runs worse when warmed up. The plugs show to be black from fuel(no oil) and they smell like gas, but no black smoke from pipes. It has a stumble when taking off from a stop(normal driving), which after driving a few miles turns into a miss throughout the rpm range,and sometimes backfires.(I think its fouling the plugs) I've tried timing all over the place, 36 total, 40+ total, 30 total and it still continues to blacken the plugs and stumble.Runs ok at wot but should make more power. Its a brand new holley street avenger 670 and I've adjusted the idle mixture screws with a vacuum gauge multiple times, changed power valves(went from a 65 to a 45) reduced the primary jets from a 65 to a 64(thats the smallest I had) changed the secondary spring to a lighter one, and checked for vacuum leaks everywhere with carb cleaner. Wouldn't a vacuum leak show lean plugs? I wonder if the marks on the balancer are wrong, its a new professional products stock replacement balancer? Any help would be appreciated. Here are some specs:

Procomp angle plug heads 190cc runners(never buy again)
Comp Cams 12-234-2 adv duration 256/268 dur@50 212/218 1000-5200 rpm
I degree'd this cam in at 1 degree advance
Edelbrock eps dual plane intake
Engine Works ready to run dist. with petronix coil
Engine has exhaust manifolds, we could'nt get headers to fit his car

[1gary]

Tech might chime in,but he recently posted that the formula to determine the size of a intake runner is .5 X the cubic inch of the engine.He also stated the compression ratio,wt of the vehicle,gear ratio,tire size,exhaust,intake,valve size,all helps to decide which cam shaft to buy.All of which I agree with.So 190cc heads do sound a bit big for a 350 street driven vehicle and that would be even more true for a low compression 350 which you hadn't stated what is that compression ratio.

[dbr25]

The pistons are about 0.025 in the hole-flattops with 64cc chambers, bore is 4.06, I didn't calculate cr, I figured it was around 10 to 10.5. Will the large runners cause a rich condition? The only way I think it could is if the fuel come out of suspension and is accumulating and running down the runners causing the richness after its driven a few miles. I 'm going to try an edelbrock 600 carb today and see if anything changes. I'm also going to adjust timing using another method, vacuum gauge instead of light, I think the marks on the new balancer or timing tab are lying to me. Wish I'd checked when I was degreeing the cam.