poor hi speed/acceleration question?

Discussion in 'Engine, Fuel and Exhaust' started by Vagabond, May 26, 2014.

  1. Vagabond

    Vagabond Member

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    just did a cam/lifter swap in a new to me 96 evo. bike has a se air cleaner with dual/drag pipes, thats it. camshaft that went in was a ev27, bolted everything back up without touching car and returned igniton to factory/as found position, went for a ride. starts/idles no prob, mid throttle no problem but transition from mid throttle to wide open, or quick crack of the throttle, pop/popping out the exhaust. roll on throttle, no problem but only when cracking throttle that the stumble appears. its in all gears but found it in 4 and 5th. went into to carb, first time found a dynojets and thunderslide that i saw/new so someone had been in there before. jets are 45/185, needle in middle position. in there, went to 195, worse, back to 185 and needle up one on the notch, worse. needle up 2, worse(test). put in a 175, better but still not good. 175 and needle back in 3/middle really good just made the symptom not as noticeable but still there, still pops. i have no expereince with these jets/sizes, it looks like there bigger than keihins, id ont know. ive never had an issue before bringin a carb in but this dynojet is killin me. this popping/stutter out the exhaust when crackin the trottle, hiway passing is not funny anymore, any help would be appreciatted. 91 actane in the tank and lines/tank are clean. pipes are un baffled but worked before with stcok cam with 185/45. im losing my mind. thanks
     
  2. fin_676

    fin_676 Experienced Member Staff Member Moderator Contributor

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    Some of the aftermarket carb tuning parts can cause issues in some circumstances in particular the slide can move to far on initial movement and then hunt for correct position giving erratic acceleration
    Jet sizes should be metric so a 175 jet would be .175 mm however the taper inside the jet may differ making one look larger than the other
    If I were trying to tune that carb I would return it to a stock parts first
    However keihin carbs tend to suffer from icing in my part of the world so on my big twins I have mikuni hsr although I have experienced no icing issues on 883 sportster with keihin carb

    Brian
     
  3. Vagabond

    Vagabond Member

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    thanks fin 676, id love to get rid of these dynojet parts, ive managed to stay away from them since the late 90's but they keep popping up. i dont have any parts now to convert this carb back, but your absolutely correct. either now i spend some money in parts or buy a used cv40 or 44. im convinced its all needle right now, as you said, flutter. id just like to find some kind of a sweet spot for now, 45/175 and needle at 3 groove. funny thing is, stock cam it had a 45/185 3rd groove and the ev27, it likes a leaner main with a needle that needs to be a trombone slide. thnaks
     
  4. fin_676

    fin_676 Experienced Member Staff Member Moderator Contributor

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    A used cv may be the answer and just build a good carb out of parts from both

    Brian
     
  5. Vagabond

    Vagabond Member

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    thanks, got my feelers out:D