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high load/rpm misfire...ignition?

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I have a piranha pit bike with the Daytona anima 190 4v motor that's been giving me issues since day one.

 

Problem: misfires past 1/2 throttle, usually only occurs past 5k, in any gear.  I can cruise to 10k with a small throttle opening no problems, and can full throttle when under about 3.5k rpm.

 

Problem does not get better or worse from 1/2 to full throttle when revs are up.  There is no popping or backfiring, just engine cut every couple revolutions that studders the acceleration.  Bike still accelerates, but does not sound happy.

 

Starts first kick, idles great at 1700-1800rpm (auto-decomp kicks in at ~1600), and runs great up to about 1/3 throttle.

 

I have scoured the forums and tried all solutions to these symptoms. Things I have tried/fixed:

 

  • Crankcase vent hose was kinked badly.  Re-routed slightly and fixed.
  • Jetting has been eliminated, since the problem persists with a variety of main jet sizes.  I tried everything from 110 to 140, stock is 125.  110 gave white plug tip, 140 gave black.  The stock 125 gives the nice golden brown during plug chop.
  • air filer is clean and oiled
  • carb has been cleaned everytime I changed jets.
  • Programmable CDI is set to 12,900rpm
  • no fuel blockages in the pet cock
  • new spark plug, nice blue spark when grounded to engine
  • valve clearances set to 0.003" and 0.004" intake and exhaust
  • TDC on flywheel matches cam notch for timing
  • oil/filter/screen changed and filled to correct level

The next step I believe is to start suspecting the ignition components, starting with replacing the coil. Are all pit bike coils universal? 

 

Please give me some suggestions or checks before I start buying parts!

Edited by damnbiker

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Run a new spark plug w/ a smaller plug gap. Smaller gap puts less strain on the ignition. Suspect the ignition if a smaller gap yields good results.

Edited by keenxxx

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Reduced the gap from the stock 0.025 to 0.017, no help.  Since that should in theory allow a weak spark to jump without issue, I began to work backwards from the coil.

 

This is when the skies opened up and the holy solution showed up and cured 95% of the problem.  Still misses at absolute WOT, but barely noticable now.  Turns out one of the pins on the connector from the stator to the CDI was bent, causing the connector to not seat all the way, by about 2mm.  I KNEW it was electrical....

I think next is to take everything apart and maybe add a smidge of conductive grease to fix that last 5%.

I've been battling this issue for about a month, and it feels so good to finally have a working bike.  The 190 pulls HARD, enough to make short work of the rear tire $$$

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