After this forums help and several hours my 3.4 engine in my 340 is running almost perfectly. The engine is from a 58 mark 1 with the original carbs on it. I have had the carbs rebuilt, all the ignition parts were replaced. New fuel tank and pump. The hopefully last hurdle to clear is after it warms up and the starting carb is turned off I still have an intermittent backfire through the exhaust. It only happens maybe every 20-30 seconds or so. I've timed it at 6 degrees before and have the carbs tuned as well as I can. The engine starts immediately cold and does run somewhat rough for a few minutes until it starts to warm. That's when I shut the starting carb off and it settles down to an idle. Any thought?
Thanks

 

Congratulations on your progress ! You've put a lot of effort into getting it "sorted". Sounds to me like its basically ready to roll . I don't have any great insights into the final sporadic backfiring issue, but if it were my car it'd get my Gunson's Colortune on both the # 6 and # 1 cylinders and make sure the air/fuel mixture was correct when the car was warmed up and idling. Good Luck !

 

+1^

 

Backfire thru exhaust could be a rich mixture or intermittent electrical issue. plug, points, condenser, coil.