340 misfire

[rm69dart]

hi guys need some advise. elec. ignition, timing set at 18, ld340 intake, 1406 carb, mild cam. runs good at idle but when i put it in drive has a stumble or misfire almost wanting to shut down. car runs good at cruising and at highway speed. where should i start looking. any input would be greatly appreciated. thanks

 

[Inertia]

What have you done to it lately ?

Look and listen for vacuum leaks around base of carb, would be my first guess,, but could change depending on the answer to the last question..

 

[rm69dart]

340 was totaly redone and was running good. this has started resently. one thing i do notice now is that when i leave the car sitting 4 to 5 days with out starting it, takes a long time to start some times i have to add gas to the carb and then starts right up. who know this may be a different issue.

 

[moper]

How was it "redone"? Was the cam updated?
The best place to start is the timing curve. You have 18° initial. Is that with the vacuum line to the distributor connected or disconnected and plugged? What ignition system? What is the total timing? When is it all in by?
After timing is the carb... What rpm is it idling at? Where are the mixture screws (in terms of # of turns out from "snug")?

 

[rm69dart]

timing 18 plugged vacuum, pro form distribitor, carb adjusted in idle soon as starts stumpling 3/4 turn out. redone machined 40 over, 360 j heads, mild cam, idle 850. timing curve and total timing i think thats really out my league.

 

[3406pk]

If engine was recently overhauled, the intake bolts could have loosened or gasket compressed causing a vacuum leak around intake. If you have a stethoscope listen for leaks around carb and intake. Then go snug up intake bolts all around. If no leaks, then check total timing @ full centrifugal advance. Should be around 30-34 for mild cam. Read some of the "Similar threads" suggested below this thread.