[AlexFIA]

For info purposes, here is what my carb set up was:

Choke - 36
Aux Venturi - 4.5
Mains - 135
Air Corrector - 175
Emulsion - F11
Idle - 50
Pump Jet - 50

After some reading and research here and elsewhere, I found that I had a lean condition down low. Tried 55 idle jet, and then went to 60. Mixture is one turn out. More than the prescribed 3/4, but close. The popping (backfiring) out of the carbs has significantly decreased and is fairly infrequent now. The backfiring out of the exhaust has been reduced by 50% or more and is much less severe. The plugs are now also a nice tan color with a black base. I'm still in the break in phase so will stop here with messing with the motor, especially with the improvements thus far. The builder supposedly tuned the carbs on a dyno and has the dyno sheet to prove it but the data starts at above 3300 RPM. Obviously not a lot of effort in setting the idle circuit. It is a reason why I do not want to mess with the main circuit anytime soon, as well as the fact that the engine runs great at the higher RPMs (for what little I have tried during the break in).

If anyone else has a similar engine with either IDAs or IDFs, I'd like to see how you are set up, or if you have any recommendations. I realize that the cam has a lot to do with it, but in general, it should be close. Would also like to hear about drivability and how your motor sounds. I don't have an issue with the way it is now, light backfiring on decel, but want to find out if it is truly a characteristing of the IR intake and header exhaust as I have heard elsewhere, or if I should be concerned about doing damage.