The V8 Owners Forum -

Afternoon, I've just got back from the 1st longish trip since building the engine, covered about 250 miles down to lands end and back, anyway the car runs fine at cruise and on acceleration but it is very jerky and stumbles with very light throttle when in traffic or around town, I thought I had eliminated this after the initial setup but it appears not. So I'm assuming it's a fueling issue but I'm not sure, could it be vacuum/ distributor based?
Basic info on the engine
Rv8 3.9 ' interim' engine fully stripped and rebuilt all new bearings and seals new timing gear and rockers, standard distributor
Real steel cyclone cam but rest of the engine standard
Holley 390 carb, 56 primary jet, 57 secondary, 6.5 power valve, 31 pump jet , steel vacuum spring
Timing 14' at idle with the vac disconnected
According to the wideband idles at 13.6-1, cruises between 13.8 and 15.6, and drops to 12.1 when you floor it, that sort of suggests to me it's not far off where it should be, but...its this lightt throttle stumble that I can't get rid of
Any suggestions or advice gratefully received
Roger

What does the wideband read at low speed cruise? It would generally have to be far too rich to cause a stumble, but only slightly weaker than it has to be for decent economy. But a weak spark will have more trouble firing a weak mixture.

When I back off the throttle from a higher speed or going down hill it leans right out to 17-18:1 momentarily, in crawling around traffic it's probably a bit rich at low 13s , but if I lean out that how would that affect the rest of the range which in general seems ok?