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421 cheetah powervalve jetting


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as i have said in PM land.  get the idle jet good first  then do your plug chops if you feel the need.  then after idle and main are good play with needle position.    most bikes i have worked with had wayyyyyyyy to big idle ( slow) jets in them. this can also cause a ok plug chop when it is actually lean.   i personally dont do chops but thats just me.

 

   in a pv motor if the idle and slow is to rich and causes a rich hesitation coming onto the pipe it will cause the pv to open slow.  you can always see this on a dyno if everything is right.  big nasty dip as your coming up the rpm's   most pv's SHOULD have a big drilled out jet or just a 10/32 mini bung like what comes with the lil bitty power jets from clippard.

 

  after your jetting, pipe combo, carb setup, ignition, dome setup, porting is all dead on you can then play with the pv open/ close time to adjust what you want OR use a dyno and after all that look at the graph and try and adjust out dips with the pv's.  if a pv motor is done right i can make excellent power from about 4500 rpm to over 11k.  top end and overrev depends on pv open time and pipe rpm peak and overrev support.. 

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