[SuperGMC]

I recently bought a 2006 CRF250X and I love it, besides the slowly leaking suspension of course. It has plenty of power, but when I use the last 1/8 or so of the throttle it cuts out. This only happens at higher RPMs. Topped it out at 65 and with the gearing this has, and with the rev limiter at 12,000 it should easily do almost 80. 65 MPH in 5th gear is around 9,400 RPM, but it feels like it's hitting a rev limiter. Any thoughts?

[JimDirt]

Welcome to the site !!

First off what gearing does it have ?? , not sure i would ever see a 250X go past 70 with stock gearing , and i think that would be pushing it , a stock 450X (stock gearing) will barely go above that (stock my 450X went about 83) , i am geared down 1 tooth so a 13/52 instead of the stock 13/51 and i top out about 75 , which i believe is where the 250X is geared (13/52)so i don't see any speeds higher than that

As for hitting the limiter at 9,000 , it could be a issue with the TPS , maybe its not advancing the ignition enough because of a setting or its going bad

Could be a lot of things , need more detailed specs as to the bike (and its history and mods if any , jetting , elevation , etc, valve lash , if possible , all can help determine the issue your having with reaching the RPM the bike should)

[SuperGMC]

Welcome to the site !!

First off what gearing does it have ?? , not sure i would ever see a 250X go past 70 with stock gearing , and i think that would be pushing it , a stock 450X (stock gearing) will barely go above that (stock my 450X went about 83) , i am geared down 1 tooth so a 13/52 instead of the stock 13/51 and i top out about 75 , which i believe is where the 250X is geared (13/52)so i don't see any speeds higher than that

As for hitting the limiter at 9,000 , it could be a issue with the TPS , maybe its not advancing the ignition enough because of a setting or its going bad

Could be a lot of things , need more detailed specs as to the bike (and its history and mods if any , jetting , elevation , etc, valve lash , if possible , all can help determine the issue your having with reaching the RPM the bike should)

I had the TPS checked out and it's good. Coil and stator are good. Carb was all clean. It has 14/53 gearing which, coupled with the 3.611 primary drive and .815 5th gear and a 100/100-18 tire puts my theoretical top speed at a little over 80. That is with the stock 12,000 RPM rev limit but I have done the pink wire mod. I'm wondering if maybe it's jetted too rich as when we took the carb apart it had a 175 or 178 main jet, I don't remember which, and there are really no other mods done to intake or exhaust except removed spark arrestor.

[SuperGMC]

As for hitting the limiter at 9,000 , it could be a issue with the TPS , maybe its not advancing the ignition enough because of a setting or its going bad

The guy I have working on it said it could be a CDI as well. Is there anything else it could be before I drop $200 or more on a new CDI. When I get it back I'll try to make a video of it and post it to YouTube.

[Leardriver]

It is drowning in fuel.
Put in something closer to a 152 main. That will be close enough to rule out jetting as the problem.

[JimDirt]

Drop $50 on Ebay (or less) and use that , it will eliminate the CDI (or borrow one from a friend , even cheaper for just a test) , also do as leardriver says , he knows carbs better than anyone else here , so his advice is solid

As far as top speed goes , if you "need" to go that fast often , then you would be happier with a 450 rather than trying to wring the neck out of the 250 , top speed is not a virtue of a smaller bore , to me a 250 in 5th is like a 450 in 3rd , at least that is the way it feels to me when i ride them , i keep looking to see if i actually have a throttle limiter , as it sure seems like it after getting off a 450 , and not saying its exactly that way , as in racing , lap times are very similar to a 450 , but if your going for top speed , nothing gives you that better than a larger bore

[SuperGMC]

As far as top speed goes , if you "need" to go that fast often

I will hardly ever need to go that fast, but I will need to have it available to keep up with my brother on his WR250F

[SuperGMC]

It is drowning in fuel.
Put in something closer to a 152 main. That will be close enough to rule out jetting as the problem.

I will see what I can do. The guy I have working on it is pretty experienced and he says it doesn't feel like a fuel issue it feels like a rev limiter. I will try to find jets to put in.

[JimDirt]

IF , it was the rev limiter , it would be popping , like cutting out (bap,bap,bap,bap,bap)really fast almost sounding like a stick of firecrackers going off , not just bogging or feeling like its holding back , big difference , which by your description it sounds more like a fuel issue as leardriver mentioned , it could be the CDI , and like i mentioned , if you "borrow" one off another bike , you will know instantly if that is the issue or to eliminate that from the problem

I am assuming you or the guy working on it has a Factory Honda Service Manual correct ?? , if so the tests will be there to check the CDI as well as Stator,Coil,etc , so hopefully he is using the specs from that for his "evaluation" as opposed to "guessing" thats what it sounds like , you/he needs to completely rule out each part one at a time , changing several things at once won't give you a clear picture as to what is going on , with each change you should either notice a difference for better or worse , or no change at all , this will eliminate or confirm each item on the checklist as good or bad

Not saying your guy doesn't know what he's doing , just adding input to the diagnosis

[Leardriver]

It may not feel like a fuel issue, but it is such an easy thing to rule out.

That bike came with a 125 main jet from the factory, I think, and I tuned one at 5,000 feet on a dyno where the A/F ratio was measured, not guessed at, and it wanted a 148 main.

A main jet is cheap, takes 5 minutes to change, and may be the source of poor drivability at high rpms when you are 10 sizes too rich.

[SuperGMC]

It may not feel like a fuel issue, but it is such an easy thing to rule out.

That bike came with a 125 main jet from the factory, I think, and I tuned one at 5,000 feet on a dyno where the A/F ratio was measured, not guessed at, and it wanted a 148 main.

A main jet is cheap, takes 5 minutes to change, and may be the source of poor drivability at high rpms when you are 10 sizes too rich.

Yeah we are going to try a 130 jet tomorrow

[SuperGMC]

It may not feel like a fuel issue, but it is such an easy thing to rule out.

That bike came with a 125 main jet from the factory, I think, and I tuned one at 5,000 feet on a dyno where the A/F ratio was measured, not guessed at, and it wanted a 148 main.

A main jet is cheap, takes 5 minutes to change, and may be the source of poor drivability at high rpms when you are 10 sizes too rich.

The stock jet for the 2006 is a #130 so that's what we're trying tomorrow. I'm guessing that's the issue. My altitude is 1,404 feet.

[Leardriver]

That was the stock jet according to the lawyers who jetted it to be legal on California trails.

The engineers who wanted to put in the proper 152 jets were over ruled, but they published a paper telling us how to uncork them to run.

[SuperGMC]

That was the stock jet according to the lawyers who jetted it to be legal on California trails.

The engineers who wanted to put in the proper 152 jets were over ruled, but they published a paper telling us how to uncork them to run.

The guy I have working on the bike is bringing a 130 and a 152 back from where he works.

[Deanzo]

My 2012 250X with that gearing, on a full top end rebuild, high comp piston, R head and cam, every other mod under the sun.

Tops out at 75 mph (122 kmph for Kiwis)

I have a Vapor installed as a speedo, it records max speed, played around with top speed runs after I did all the mods.

Before 50% of the mods (never did stock) 72 mph
With the mods, gets there much faster.