Part throttle stutter, help.


5 replies to this topic
  • 309

Posted August 10, 2004 - 07:52 AM

#1

Ok, here goes, bike is a very heavily modified '01 WR426.

I'm getting a stutter at part throttle that has me baffled. Up to 1/3rd throttle, it runs fine. Steady 1/3rd and above throttle at low speeds, it stutters bad. If I'm nailing it, it revs right up with no stutter at all.

I believe this to be a new development, but can't be too sure, as I hardly ever run it like this. I have noticed it riding around my neighborhood. Normally I have only ridden this bike (supermoto) on a go cart track where it was being ridden in a manner where I may not have revved it gently or held steady throttle like on the street. It also seems to be intermittent, as I've thought I had it fixed, then had it come back. Fun.

The bike has an Edelbrock carb, so TPS is ruled out. The carb has been cleaned. The sparkplug is new. All possible "jetting" type fuel adjustments have been tried and made no difference. Fuel has been drained and replaced. Petcock has been cleaned out.

Seems like fuel has been ruled out, so I'm guessing ignition is the culprit. Again, new plugs have been tried, no difference. I've checked all wiring connections, as well as cleaning them with contact cleaner. There are quite a bit of things disconnected and removed from the harness as this is a race bike, but I've never had (or at least noticed) this kind of problem with it before.

CDI?

Coil?

Can anybody tell me if these may be the culprits? I do not have an OHM meter, and I won't have access to another CDI and Coil until this evening, so testing these would have to wait until then.

I'm looking for advice on any other things I might try in the meantime. I'd also like to know if people think i'm correct in suspecting the CDI and/or coil. The CDI is a "factory" Yamaha unit, not stock.

Any help is appreciated.

  • 707

Posted August 10, 2004 - 07:58 AM

#2

Maybe Check valve clearance.

  • 707

Posted August 10, 2004 - 08:00 AM

#3

Maybe your top end is bad. SInce its been raced.

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  • 309

Posted August 10, 2004 - 08:11 AM

#4

The motor is fresh, but tested, has one race and a bit of track/street riding on it.

  • 309

Posted August 10, 2004 - 08:36 AM

#5

Just checked valves, all right on spec.

  • Gizabious

Posted August 10, 2004 - 02:45 PM

#6

I had the same problem with my yzf apparently a common complaint on yamaha 4 strokes. Turns out it's more jetting related than anything else, i was able to cure the problem by leaning the needle 1 clip position also richened the pilot from 42 to 45 to stop the hesitation off the bottom.





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