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2009 Honda CRF250R jetting

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Hello fellow MX racers, I just bought a brand new 2009 Honda CRF250R because I think it’s the best CRF250R ever built. I strongly believe I can still challenge some of the new machines on the track racing this bike.

I’ve read many articles on how to twitch the jetting but none addresses my dilema. Along with the new bike, I’ve spent some money buying several aftermarket parts (including exhaust system) to make it race ready so my budget for extras is almost gone. This said I need your expert advice on the following 2 questions:

1) What is the best way to eliminate the annoying bog between these 2 options: 

  • Swap the 40mm Keihin carb for a 2004-05 37mm or
  • Install the R&D Power Bowl 2 to the stock 40mm carb (which MXA magazine gave it a 5 star rating)
  • (Maybe doing both is the best way to go but right now I don’t have the budget to do it)

2) I live and race 5,000 feet above sea level, our average temperature is 71 degrees and 75-80% humidity. Considering these factors, your response to the previous question and the fact that I installed a brand new MXA 5 star rating "Dr.D single side exhaust system" (muffler and header), what would be your suggested proper jetting settings?

I will really appreciate your expert advice.

 

Thank you

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The R&D Powerbowl two will have no affect on the oversize carb issue.

Your 2009 carb already has all the latest accelerator pump upgrades that were done in 2008.

The Powerbowl will not improve this. It will improve partial throttle response, but that's not really needed for groomed terrain riding.

Fine tuning the stock carb will help: 55 leak jet, and checking the squirt timing are on the top of the list

Correctly adjusting your fuel screw (use and R&D fuel screw) will keep things crisp.

 

 

The 2009 had limited top end pull, but it is still the best stock carb motor for 2009

The Dr D pipe will not help this! It is a 'torque' pipe.

The Pro Circuti T4 or Yoshimira is what you want for more top end.

The Dr D pipe will make it run better, and make it easier to ride.

 

The very best thing you can do to that motor is to get the head ported for a wider power band

This will give you more power everywhere, making the bike much easier to ride in any gear, and pull harder

 

Stock jetting is actually fine for that bike.

 

You can play with needle height (lower it) for your altitude, but you are still far from being 'too high' for the stock jetting.

 

 

Q: WHAT DID WE DO TO THE STOCK JETTING?

A: Our best fix was to richen the pilot jet, leak jet and needle. Here are MXA’s recommended jetting specs:

   Main: 185
   Pilot: 45 (42 stock)
   Needle: NNWT (NNSU stock)
   Clip position: Third from top
   Fuel screw: 1-1/4 (2-1/4 stock)
   Leak jet: 60 (70 stock)

Edited by TheKoolAidMadeMeSick

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Thank you very much for your quick and detailed response, you just saved me some serious bucks !!

 

In conclusion, your suggestion is that I keep the stock carb and don't buy a 37mm right? Back in those days I remember the MXA guys alway praising the 37mm carb in contrast to the bigger one so this why I asked....

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