OK, got a 355 sbc ported heads (284/237), comp nx274 hyd flat tap, 10.3:1 with domes, all forged bottom end. right now imusing autolite 24's with a .040 gap. I tried .045 and the plugs were fowling kind of easily, so i thought maybe .040 would be better. Well, i've got an accel coil and distributer and it sounded like i overreved @ 5900 RPM. Now that should not be happening with my heads and that cam is rated 2500-6500. Is that .040 gap too small or too big, and coiuld it be that my plugs aren't cold enough or too cold. they're 2 steps colder than stock.

 

If you are getting fouling of the plugs, they are either too cold, the mixture is too rich or the ignition is weak and misfires are leaving you with a lot of unburned fuel. Since it doesn't seem to want to rev over 5,900rpm, sounds like the ignition system is weak, or the tune is way too rich. Two steps colder than stock shouldn't be a problem, unless the tune is off. Carb or EFI?

 

i think my coil is like 45,000 volts, and it was running a little but rich. but what about that gap? is .040 enough?

 

Pull a plug and let us know what it looks like. A good hi-res photo would be even better.

.040 is fine and I agree it's either rich or you have low spark intensity. And knowing whether carb or efi would help with the route for your fix.
Are you sure there's no oil fouling???

-Mindgame

 

oh sorry, its a carb, 750 speed demon. the plugs looked completely black, so its really rich. i cut the fuel back alittle when it started missing, and that stopped it. i guess its just rich then.