Have a 67 coupe with a 200ci i6 and 3 speed manual. At idle, the engine appears to run smoothly, with the occasional pop, or stumble. During accelerating, 1st gear is fine, but in 2nd it is rough and appears to stumble. Once at cruising speed in 3rd the engine is smooth. Check the timing and replaced the vacuum line on the distributor, still having issues. Any ideas?

 

look at the plugs.

try a different set of plug wires.

inspect points. if they are pitted replace them.

check points gap. it should be .025".

remove distributor vacuum.

turn fuel mix screw to jihjest idle the turn it out 1/8th turn more.

reset idle.

check timing at idle with without dist vac coinnected to ported vac [not manifold vac] and also with it disconnected.

do the same at 1600 rpm or 1/4 throttle.

do the same at 2800 rpm or near 1/2 throttle.