[Mtngoat00]

Hi all, hope someone can help. I have a 2006 CRF250x. It was running fine until the other day after a 2 hour ride when it began to sputter and then konked out. Luckily I was at the top of a hill and coasted home. Now it will start when cold but after a few minutes of riding it starts to bog down then quits, usually about 1/4 - 1/2 throttle. I have taken the card off and cleaned all the jets and even took it to the shop. The mechanic said it seemed to run ok for them and all he did was clean the flat bowl for $150!! I have also flushed out the tank, cleaned the in tank fuel filter and put in new clean gas. What should I do next??? Just do a total re-build of the carb? Could it be something else. I did check the gas cap vent. thanks for your help.....goat

[JimDirt]

Welcome to the site !!

It sounds like it might be vapor locking , if your certain the vent tube and the gas cap it self are both free flowing (Is the vent tube a aftermarket short anodized one or just a straight stock tube ??) , by your symptoms it sounded like the vent tube , by chance have you checked the actual carb vent lines , under the bike , and made sure there is no mud clogging them up from allowing the carb to vent ??

Have you verified a strong spark AFTER the bike gets warm ?? (when it starts to act up) , it could possibly be a electrical issue , by either a loose coil wire (where the power plugs into the coil) , or a stator going out

Is it backfiring thru the muffler when it starts dying out ?? ,(only on Deceleration) if so this would indicate a lean condition , if its not backfiring i would think its more of a electrical issue than a fuel issue , where its possibly losing spark under load or heat (electrical parts tend to break down when hot as opposed to a cold bike/electrical part) , as you stated that it seems to run fine when cold but as it warms up it runs worse

you need to eliminate some things first , is the AP pump squirting ?? , does operating the hot start while riding make any difference , (this might tell if its a fuel issue , as the hot start should lean the system) , is the actual gas cap venting ?? (besides the vent tube itself) , is the float level correct ?? , a low float level will allow the bike to run , but it can run out of gas when running the bike above idle for any length of time , until the bowl fills back up , but this is usually noticed by bogging , then when left at idle for a minute or so , it runs good again , then as it is ridden it bogs again

[Mtngoat00]

Thanks JimDirt...very excellent advice. I will check things out and let you know.

[Mtngoat00]

Ok, some progress: the shop thought it was the ignition coil which they replaced along with a new plug. It ran for about 2 hours then again on a steep down hill it sputtered and died. After 45 minutes I got it to turn over and start but I had to totally redline it to keep it going. Needless to say this was not a happy machine. After about 5 minutes it was red hot with flames out the pipe. I shut it down and we towed it home. The next day I pulled the plug. It has a thin black coating but no real thick deposits. I carefully brass wired it clean and re-installed it. The bike fired right up and seemed to run but it is a bit rough. Any ideas? The carb is totally clean, all vent hoses open and tank venting well. Any diagnostic tips? goat....

[Mtngoat00]

Oh, when I got it back from the shop it was running but back firing a lot on deceleration. You said that would indicate a lean condition. As a trial I opened the fuel mixture screw 1/4 turn and this seemed to decrease the back firing. I have ordered new jets and was planning on opening the main and pilot jets a little. I also noticed when I cleaned the carb the needle had only one position for the c-clip....I have ordered a new needle that can be adjusted. Any suggestions?

[JimDirt]

Sounds like your on the right track , though i would sustain from reaming out any jets , but rather just see what you have , and replace the Pilot Jet instead of cleaning it , if you don't have a actual Jet Cleaning Tool , you will ream out or clog worse the jet and be right back where you started , a pilot jet is about $6 , so its not much for conformation that there is no restrictions , which will aid in being able to actually tune it properly

Yes a adjustable needle will help with fine tuning , but its mainly going to be for mid range tuning (how soon gas flow increases thru the main jet) ,idling/low RPM running is controlled mainly by the Pilot Jet and Fuel Screw , so the popping is a indication that its in the primary circuit of the carb , i would also while you have the carb apart , check the operation and cleanliness of the Hot Start , where it goes into the carb the brass plunger can get deposits on it that will make it stick or partially stick , which can also cause a lean condition (the Hot Start actually leans out the mixture which makes it easier to start a bike that has fallen over and flooded , or when starting a hot engine where you want LESS not more fuel to get it to start) , so make sure the plunger is clean (i use Steel Wool for the plunger itself)

Try that , then report back , it should be a noticeable improvement (don't forget FRESH gas)

[Mtngoat00]

Hi Joe, I did not mean ream out the jet but replace with next size up. Anyway, I will follow your advice and see if anything improves. Do you think increasing the size of the pilot and main jets is a good idea? I assume this will enrichen the mix a bit.

What is your thought on air box modification? I see a lot of discussion about it. Why don't people just get rid of the air box all together and use the clamp on type filters???

Thanks for your help. your humble gumby, goat

[JimDirt]

lol , its JimDirt , not JoeDirt lol

If your going to open up the airbox , i would first concentrate on getting it running good "as is" so as not to compound your issues , the more you do without sorting things out , the harder it will become to sort them out ... follow ??

IF you were to open the airbox , usually the main will remain the same (not always , but usually) , its the Main Jet that is affected by the airbox opening more than the pilot , since any adjustments can be made with the fuel screw for most compensation

Again , once you have it running "normally" with this setup , THEN you can start altering things , IF , while adjusting things in current configuration (with a new Pilot Jet) and you can turn the fuel screw out or in more than the specifications recommend , THEN is when you would change the pilot jet either up or down 1 size to compensate for the out of limit settings ....follow ??

As for filters , you dont want to Macgyver things like that , the one thing that is DEATH to these engines is DIRT , even a little slipping past a filter will eat your valves quicker than you can imagine , if you find even a slight amount of dust inside the air boot , it means your not sealed and dirt is entering the engine , yes even fine dust will kill the valves , its the most common issue why people have to prematurely replace valves , the airbox design (minus allowing more air by opening it up) is designed , as are the filters , to address this issue , and altering the intake tract by eliminating the air boot and airbox , will cause a expensive death to your engine

So cut the top .....YES , Remove the airbox , NO !

You should be around #40 Pilot and #130 Main Jet , and about 2 turns out on the Fuel Screw , any less than 1 turn out to run correctly , or more than 3 turns out would require the next jet size down/up

But search thru this and see what everyone else is running around your elevation

*note that some have modded airboxes , so take that into consideration , as it will usually change jetting from "stock" settings for the same elevation*

http://www.crfsonly.com/forum/viewtopic.php?t=13472