4 stroke hei wont run at low rpms

[g5mod]

Ok, I picked up a 91 yamaha 4 stroke without a working cdi/igniter so I installed a HEI module as per diagrams on this site. If i start going down a hill it will take off and run like a bat out of hell! I can slow down and acellerate fine. when I stop and try to start again it backfires sputters blows smoke out of the carb and exaust. I cleaned out the carb, made sure i have good grounding and tried different coils and reversed the pulser leads. what am i missing? The only thing I dont have is an air box, is that required to run?

[DustyWolfe]

no and i say that being careful cause many people here will tell you otherwise and they are right for the most part. if you are keeping the stock jetting then yes the airbox is important... however if your planning on changing jets(probably should anyway cause from what ive seen they all run lean) then the stock airbox isnt neccesary as long as you have an air filter of some sort(like a uni pod filter). and lean jetting can cause your symptoms although usually its at high rpms not low(not saying it cant be). id try cleaning your carb first before i go spending anything on it.

[g5mod]

thanks ill go thru the carb again to make sure its ok. To me it seems like the timing is out at start up, any thoughts on that? is the hei mod supposed to work on all 4 strokes?

[DustyWolfe]

not really sure about the hei mod. but i believe the only way to lose your timing is if the key that holds the flywheel in the correct place on the crankshaft is sheared off. otherwise im pretty sure its set in stone(i suppose i could be wrong). the coil shouldnt have anything to do with timing just gives you alot stronger spark for cheap.