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2003 CRF230F Surging Top End

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Hi all -

 

Picked up a 2003 CRF230F late last year.  It is really clean and in excellent shape.  I re-jetted to a 102 main jet and kept the 45 pilot.  The bike seems a bit weak in the top end and occasionally wants to surge.  The carb is really clean and it has fresh fuel.  Seems like a fuel delivery problem but I suppose it could be electrical.  Any ideas?

 

~DS

 

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Float level is fine, fuel supply at the carb is good (ruled out petcock).  I ride between 8000 and 10000 ft. altitude, hence the smaller main jet.

 

Forgot to mention - bike is stock, no mods.

 

~DS

Edited by DeadSpider

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Float level is fine, fuel supply at the carb is good (ruled out petcock).  I ride between 8000 and 10000 ft. altitude, hence the smaller main jet.

 

~DS

 

Okay - Great.  Let's have a look...

8,000 feet = 93% AP = 112 main

10,000 feet = 92% AP = 110 main

 

I'd say you're a little bit too lean.

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Well that is interesting.  Stock jet at sea level is a 102 main 42 pilot.  If what you say is true well, that's certainly the problem.  I'll try different jets and see if it helps. Thanks :)

 

~DS

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Well that is interesting.  Stock jet at sea level is a 102 main 42 pilot.  If what you say is true well, that's certainly the problem.  I'll try different jets and see if it helps. Thanks :)

 

~DS

 

Keep in mind the stock jetting is designed for use with the intake restrictor in place and is incredibly lean.  Mike Coe has done extensive dyno work and has found a 120 main is ideal for sea-level riding conditions with the intake restrictor and exhaust baffle removed.  He found the 120 is actually slightly rich but given the fact these engines are air cooled and are ridden when it's cold he thought the 120 was the most appropriate safe choice.

 

Please keep in mind my recommendations are for a bike with the intake restrictor removed.  The restrictor acts like a choke, increasing signal across the circuits and, therefore, making the mixture richer.  Removal of the intake restrictor makes the carb meter leaner so you must compensate by installing bigger jets.

Edited by VortecCPI

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Update - installed a 110 main yesterday and that really helped.  Top end is definitely stronger and it is no longer surging.  I did remove the intake restrictor as well.  Thanks for the help!

 

~DS

 

Glad to hear you've made some progress.

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