bbc breaking up!

[427cutlass]

I have a 496 bbc, 850 mighty demon, holley strip dominator, 781 heads with bigger stainless valves etc, msd 6al with blaster ss coil and msd 85551 distributer. Fuel system is aeromotive ss pump, with -8 return system with sumped tank.

So heres my problem, have an engine miss from idle to 3500 under load. Revs great , just seems to do it while i cruze. I sent the carb back to demon and they set it back to factory which helped slightly. Ive done all the obvous things, plugs, wires, checked grounds etc.
big race comming up, not sure whats next...

 

[toxicbu]

check the floats .

 

[427cutlass]

demon dyno tuned the carb on a 502 crate... float levels are good, little over 1/2 up sight glass. fuel pressure is at 7.25psi

 

[Bar50]

Try a one notch hotter and one notch colder plugs.
Street driving a big compression motor will kill the plugs.
Got volts? Takes 14 or better for most ignition systems to put out correctly.

 

[toxicbu]

wish i could hear it

 

[427cutlass]

ya i have 14volts when engine is reved, have tryed diff plugs.... just tryed running a heaver advance spring on the dizzy and it got slightly better.... timing is at 19deg. @ idle, 40 total

 

[bbc_cutty]

i dont have much good to say for demon carbs, you either get a good one, or a lemon, and theres alot of lemons out there

i havent found a demon carb to be consistent, swap with a holley and see if it makes a difference, id also try replacing the coil

 

[Damon]

I had an MSD 6-series go flaky on me in the same way you describe- popping and missing under load below about 3000-3500, fine above that. In my case it also had a miss when revved over 5K under no load.

If you've got a module to put in the distributor (or a spare HEI distributor laying around) put it in and try it out. That's what I did and I never put the box back on again- ran better than it ever did with the 6 on it.

 

[427cutlass]

tryed swapping carbs, no change, also swapped in a hei and eliminated 6al, same prob....

 

[lurchsmalibu]

One cylinder missing under load? or more?

Do you think a lifter is crapping out?

Arcing inside the dis. cap?