Motorcycle Repair: Yamaha V Star 650 misfire at high rpm, throttle position sensor, air fuel mixture

Question
My 2000 V star 650 Classic has been modified with a Kuryakyn Hypercharger, rejetted with 130 Mikuni main jets, the needles shimmed to the top of the “T” with 2 Dynojet washers, and Mikuni 35 pilot jets with PMS screw turned out 1.25 turns. The carbs are balanced and the exhaust is Jardine slash cut slip ons.  The bike will go to the redline without a problem in 1st or second gear as long as the throttle is not cracked past 1/4.  When the throttle is 1/2-full the engine breaks up at high rpm like the rev limiter is kicking in.  Does the Yamaha rev limiter only cut the spark to the rear plug?  The front plug is a nice tan and the back plug started with an oval shaped soot pattern that has progressed to completely sooted during my roll on tests.  I have replaced the plug and the problem is still there.  I have adjusted the throttle position sensor to give the correct output (I thought that was the problem after the mods).  Any suggestions will be greatly appreciated.  Thanks...  Russ

Answer
Hey Russ,
Well for starters, your bike came stock with #100 mains. Bumping the main up 9 sizes is just a tad too much unless youve done some wicked engine mods (ie: cam, big bore, decked heads, etc.) A hi-flow (hypercharger) and exauhst (slip-ons) is not nearly enough to jet your carbs they way you did. So heres what you need to do.....
Put your stock mains back. I know youre thinking "why did I bother to spend the money if im not putting them in?" Trust me, after this your bike will run like a top and perform as you want it to..
#1, Put your TPS back where it was unless it was off to begin with...then,
Take the stock pilots and throw them away, you need 1, yes 1 step above stock, possibly 2 steps, but 1 is plenty. So you need either a #22.5 OR #25 (id go with a #25)
NOW, put the Stock needle back in also, HOWEVER, take just one of your shims and put it between the needle and the carb body. The last thing here is to turn your air/fuel mixture screw out to 2 1/2 turns out from the seat. (2.5)

I know it seems like were going the wrong direction with jetting but let me explain.
This is a 650cc bike you jetted as an 1100cc. OK, the throttle works like a clock (sorta) 0-1/4 turn of the throttle is ALL on the pilot jet AND how far the needle sits off the main jet. 1/4-FULL is all on the MAIN. So now this might make a bit more sense seeings up to 1/4 throttle the bike will rev, but slow, and when you wick it wide open, the plug fouls due to too much fuel from the main.
Main jet: Stock - 1/2 step up to 102.5
Pilot jet: #22.5 - #25
Main jet needle: Stock with 1 shim under needle
Air/fuel screw: 2.5 turns out from seat

Believe me, your bike will perform as your asking it too if you follow this to a Tee..

Hope this helps!


~Mark