'03 Motard, Miss at high rpms


2 replies to this topic
  • Bus

Posted April 01, 2009 - 02:40 AM

#1

Need help troubleshooting a problem with my motard. I had an '01 426 that had a trans problem. In fifth it would run out but at upper rpms it would actually pop in and out of gear (broken dogs). I decided to go with an '03 (auto decompression is my favorite thing in the world), got the bike together with my motard suspension and brakes. Ran the engine on a dyno, it sounded good and made one more hp than the modified 426. So, alls good right?

Well, running at Jennings GP this past weekend it ran well pulling from low or mid rpms, but had an occasional missfire at upper rpms. Second session got worse. I pulled a plug and it was bright white. So, with help from some friends I bumped up the main from 168 to 170, and also cleaned out some dirt I found in the carb. went back out and it sounded worse. The miss seemed to be accompanied by some mechanical "chunk" sound.

So, I rode my GSXR the rest of the weekend and still had a good time.... now, what to do with the YZF? The clutch seemed a little slow on the uptake, so I thought I'd start there... but the next step, as far as I can tell, is a complete tear down? Any suggestions?

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  • Bus

Posted April 01, 2009 - 05:09 AM

#2

All stock 03' 450 engine and trans, by the way. running 15/36 gearing (limited to about 100 mph), but have a 16 tooth front for the next time out and a spare swingarm for modifications... should give 110mph... should be perfect for Barber!

  • jjj109

Posted April 01, 2009 - 10:02 AM

#3

[quote name='Bus']Need help troubleshooting a problem with my motard. I had an '01 426 that had a trans problem. In fifth it would run out but at upper rpms it would actually pop in and out of gear (broken dogs). I decided to go with an '03 (auto decompression is my favorite thing in the world), got the bike together with my motard suspension and brakes. Ran the engine on a dyno, it sounded good and made one more hp than the modified 426. So, alls good right?

Well, running at Jennings GP this past weekend it ran well pulling from low or mid rpms, but had an occasional missfire at upper rpms. Second session got worse. I pulled a plug and it was bright white. So, with help from some friends I bumped up the main from 168 to 170, and also cleaned out some dirt I found in the carb. went back out and it sounded worse. The miss seemed to be accompanied by some mechanical "chunk" sound.

So, I rode my GSXR the rest of the weekend and still had a good time.... now, what to do with the YZF? The clutch seemed a little slow on the uptake, so I thought I'd start there... but the next step, as far as I can tell, is a complete tear down? Any suggestions?[/QUOTE

still sounds like a jetting problem. depending how cold it is and what you have done to the bike you could probably still go up on the jetting. I ran as high as a 178 main in my old 2003 yz450f. I had some mods done to her also. Also you have to keep in mind your riding that bike as a SM bike. You guys ride in the upper rpm range a lot cause of the long straights. still probably running too lean up top. check your accellerator pump timing it could be off? just make sure you recheck all your basics before tearing her apart. check the engine timing also. really easy to do. :thumbsup:





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