Mid Range Stumble

[68Camaro396]

First off thanks to everyone on this site, it is full of invaluable information. I recently aquired a '93 K5, ran fairly strong but smoked like crazy even with the carb leaned way out. It ran decent but was hit or mis on power, pin it and sometimes it would take off but mostly fall on its face and stumble and smoke. I did a vacuum test and it leaked terrible, further inspection found that the left hand crank journal was spun and had about 1/16" of radial play. I tore the engine out and disassebled it, found that everything must have been gone through recently as everything was extremely clean, wiesco piston was like brand new, jug had been sleeved(could still see cross hatch), everything except the crank bearings and seals. So i put new bearings, seals, a good oem crank, new clutch, and did cut a window in the piston and make a kips bolt myself( thanks to the resources on this site). Well to make a long story short just got everything back togerther a  couple days ago. It ran way stronger but still has kind of the same mid range stumble. Up to quarter throttle is good and responsive and if you twist the throttle wide open it really comes alive. It is still fun to ride, I just want to figure this stumble out; it acts like it is too rich. I lowered  and raised the needle clip, but it ran worse both ways. The stumble seems worse when bike is colder and the throttle is rolled on more slowly. I think the stator could be at fault as it is in rough condition due to water getting in through the cover at some time in its past. The bike has weak spark but all the components ohm out within spec. Could be a carb tuning issue but every change i make just makes condition a little worse. Anybody's  input would be appreciated.
             Current specs are compression: 180 psi, timing on middle mark, 168 main and 58 pilot at 1 1/2 turns, FMF woods pipe and powercore silencer, stock gearing, window piston, kips bolt mod and kips are working and timed, running dominator amsoil at 32-1, plug looks dark brown, i am at around 3300 ft elevation, 55-95 degrees f, and just ride for fun burning down back roads or occasional hill climb.

[Polar-Bus]

First off thanks to everyone on this site, it is full of invaluable information. I recently aquired a '93 K5, ran fairly strong but smoked like crazy even with the carb leaned way out. It ran decent but was hit or mis on power, pin it and sometimes it would take off but mostly fall on its face and stumble and smoke. I did a vacuum test and it leaked terrible, further inspection found that the left hand crank journal was spun and had about 1/16" of radial play. I tore the engine out and disassebled it, found that everything must have been gone through recently as everything was extremely clean, wiesco piston was like brand new, jug had been sleeved(could still see cross hatch), everything except the crank bearings and seals. So i put new bearings, seals, a good oem crank, new clutch, and did cut a window in the piston and make a kips bolt myself( thanks to the resources on this site). Well to make a long story short just got everything back togerther a  couple days ago. It ran way stronger but still has kind of the same mid range stumble. Up to quarter throttle is good and responsive and if you twist the throttle wide open it really comes alive. It is still fun to ride, I just want to figure this stumble out; it acts like it is too rich. I lowered  and raised the needle clip, but it ran worse both ways. The stumble seems worse when bike is colder and the throttle is rolled on more slowly. I think the stator could be at fault as it is in rough condition due to water getting in through the cover at some time in its past. The bike has weak spark but all the components ohm out within spec. Could be a carb tuning issue but every change i make just makes condition a little worse. Anybody's  input would be appreciated.
             Current specs are compression: 180 psi, timing on middle mark, 168 main and 58 pilot at 1 1/2 turns, FMF woods pipe and powercore silencer, stock gearing, window piston, kips bolt mod and kips are working and timed, running dominator amsoil at 32-1, plug looks dark brown, i am at around 3300 ft elevation, 55-95 degrees f, and just ride for fun burning down back roads or occasional hill climb.

You need to isolate exactly what the engine is doing during the mid stumble. Find a long stretch of dirt road, and accelerate and as soon as you feel the stumble keep it there for like a min or two.  Then with the throttle still held open, abruptly kill the engine. Now pull the plug and see if it's wet or dry. You might have an air leak (lean) . Your jetting seems to be in the ballpark... I also don't think it's your stator, usually you either have 100% spark or you don't. I have read of an ocassional external coil "heat soaking" and becoming weak, but your problem seems to be more throttle related.