[Dave Bilyk]

The misfire occurs only under moderate to wot acceleration so you can only test on the road. If you just rev the engine at a standstill, its fine, (secondaries dont open). Today I have checked the distributor, adjusted timing (2 deg out) and checked cleaned and gapped the plugs. Still does it.
Now, I can take it to 4000 and accel gently through to 6000, but if I give it wot, it bogs down at 4000 and makes that fluffing noise. What I now believe to be the reason is that the vacuum operated secondaries start to open at that point, but arent supplying fuel, so the mixture goes too weak to run.
Under low acceleration, the secondaries dont open until 5500 to 6000 hence it runs normally at low throttle. Next I will have a look at the float level in the secondary chamber and adjust.
Any advice from Holley experts welcome.

Dave