vp race fuel

3 replies to this topic
  • factorymark343

Posted February 09, 2002 - 08:55 AM


hey all you jet experts out there! i just got back from the vp guys place to get some fuel, i asked him about some jetting specs for running it and told him what you guys say and what i thought.he told me that we are all wrong. that the way to make the bike run better is to lean the main jet and the needle. richin the pilot jet but not to richin anything else. he told me that what he has seen from the pros and from him self that riching the main and needle makes it run worse. so just playing around one day i leaned the needle and it seemed to run better. i never leaned the main cause i did the bk mod and you all said to richin it so i did man it ran like crap so i went back to stock. im goin to florida for ten days of riding and testing so im goin to take all my jets and try a few things. let me know what you guys think!!!

  • Boit

Posted February 09, 2002 - 09:04 PM


I have no idea what the conversation was like that you had with this guy, but I noticed right way that you made no mention of which particular VP fuel he was talking about. MR2 and C-12 vastly different fuels since one is oxygenated and the other is not. Besides, you can test identical year 426's and they might each require different jetting. What I'm getting at is there are too many variables involved to make a blanket statement that VP fuel requires a specific jetting. What about altitude, temperature, and humidity? Not to mention which particular fuel he was talking about.

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  • freestyle111

Posted February 10, 2002 - 01:17 AM


5 or 6 years ago Boyesen built me a motor for my kx125.i couldnt believe the jetting difference compared to stock motor.stock 168mj,nj.3rd position,38pilot.the new motor boyesen built 150mj,nj.4thclip,52pilot.you would think bike would have less hp with smaller jets but this motor ripped.it was fastest 125 ive ever ridden.its only downfall was i needed to fine tune jetting for riding conditions everytime i rode it.it seemed like slightest weather change had affect on it.thats probably due to the fact i had to run 112octane racegas

  • Boit

Posted February 10, 2002 - 08:46 PM


Freestyle: you've added an excellent addendum to what I was saying. Jetting specs for any bike, fuel, temperature, humidity, etc is merely a guideline. It's meant to be a baseline from where to begin the fine tuning process.
One of our fellow TT'rs, James Dean, has done a ton of research and testing with the FCR carb. He as even gone so far as to have special needles machined that have multiple tapers. Very intersting stuff. He has developed a spread sheet for jetting and needles that will get you very close to spot-on once you plug in your specific information. This guy is very sharp.

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