XR250 Expert needed

hey guys i have a VERY strange problem i have seen a few times while riding my XR recently.

first i should list the upgrades on my bike

pro circuit T-4 exhaust, K+N filter and rejetted carb. i dont remember the exact size of main jet i installed but i belive it was slightly richer than stock. i am at 6500 feet and the upgrades left it running lean.

recently i have noticed that under some special circumstances my bike will flat out quit on me. as in loose all power like someone pulled the plug wire off the engine. in every case i was either shifting or had just shifted to the next gear. to me it seemed like maybe i ran the float bowl dry because when i let off the throttle and back on again it seemed to pick up and run fine again, abeit a few backfire pops then im back in business again.

i thought perhaps my filter having not been cleaned may be the culprit and maybe running wide open was running rich enough to suck all the gas out of the carb before the tank could refill it. so i cleaned that and figured my problem was gone.

yesterday i was riding in the mountians and not really pushing the engine that hard and as i shifted i belive i may have missed a gear or shifted between gears. i couldnt really tell because the engine has just started coasting down, no pops, no bangs, no nothng it was like i was holding the kill switch.

i cant be certain if i heard what i thought but it made a sound that made me think a valve was held open. if i had to guess it would be exhaust because there was no back fire in the carb or the exhaust. it very well could have been my imagination as i have never actually heard the engine in a high rpm coasting down situation and it may have been normal engine coasting sounds with out the exhaust popping so loud i cant hear the engine running anyway.

but after i grabbed the clutch and down shifted again and let the clutch out again it seemed to roar back to life no problem.

i then found a stretch of straight road and did a couple more sprints and upshifted each time it seemed to be about max rpm and no problems. this issue seems to come and go. i cant tell if it has somthing to do with the terrain i am riding on or not. i began to wonder if maybe the bumps on the road was shaking the carb enough to cause the float bowl not to fill completely or somthing.

the only reason i suspect this is because on paved roads i can throttle it all day long and no problems. i even had some punk kid in a 89 prelude 2.0 SI try to race me from a light on my way home and with a full throttle start and holding the throttle wide open and speed shifting the clutch and gears all the way to about 70 mph in 6th gear i had no problems. (he lost BTW)

every tme this has happend i have been under full throttle and on a bumpy surface. every time it has been while changing gears or going through gears on a rapid acceleration run.

after the last time (yesterday) it happend 2 times. it was hard to tell when i lost power if i was between gears and maybe let the clutch out too soon. i just dont know, when it happens i try to down shift and that seems to resolve the problem and it runs fine.

i have no idle problems, no hesitation, no rough running nothing.. otherwise the bike runs perfect every time.

the bike has about 600 miles on it and i bought it new.

is there any way i could be accidently hitting the rev limiter? if you hit it does the engine cut out for a few seconds? in a car it just wont go any faster. i dont know if bikes are any different.

is there some sensor that detects you hitting neutral or between gears to cut the motor?

is there any way i could be floating my valves? (i would assume that would distroy the engine)

i seriously dont think i could have pulled the decompression lever as i have it positioned down and have to reach to grab it.

i just dont get it, what could i be missing?

My bet is the float level is too high.


Have you checked your decomp cable adjustment? A poorly adjusted cable would normally only cause a problem when turning, but something to look at, anyway....

One thing to check that caused me problems a couple of times, sometimes got gas overflowing out carb, other time wouldn't start. Had my son pull me with ATV and it kept backfiring.

There is a little white (natural) color plastic thing in the carb that fits loose over the jet. It came out of position and would hold the float from moving freely. I just took it out and have had no problems since.

If you think it may be carb related, something to check anyway.

Just to add something else to look into...

You might check all electrical connections. A loose connection might explain why it seems to happen more often on rough roads. I'd look at simple things first like the spark plug wire, etc.

I'd say float level is too low causing fuel to shut off before the float bowl is full causing the bowl to empty enough on hard throttle that when the bike is bumped around the fuel is sloshing away from the main jet.

every tme this has happend i have been under full throttle and on a bumpy surface. every time it has been while changing gears or going through gears on a rapid acceleration run.

sound like its starved for fuel, float level perhaps too low, or restrictive flow on fuel supply, before doing anything remove the 17mm nut at the bottom of bowl look to see if there is small sediments , if there is which is often the case these sediments are the partial cause of the bockage, it would be wise to check the float just he same


thanks for all the responces guys, how do you check the float level? i mean since you cant see in the bowl do i need to remove the carb and take some measurements on the float? what should it be set to. usually you bend a tang on the float mecanism to adjust.

so are we ruling out any possibility of a rev limit cut off? i was thinking fuel also my only problem is that i cant duplicate it on the street.

At this point it might be best to get a service manual. Here is a link to one on Rocky Mountain ATV/MC.

Buy a "Honda Service Manual". (under $50) If you don't have it, you need it.

I doubt it's the rev limiter, normally when you hit the RL it still runs, it just runs crappy.

Fuel or electrical, process of elimination.

I would start with the fuel.

Stock MJ is 132, you shouldn't be any larger than 135.

PJ should be stock, 45.

For this, I would probabaly take the carb off.

Verify the jet sizes.

Verify the float level, with carb off, remove bowl, hold the carb and put the fuel line in your mouth, the floats should be hanging, you should be able to blow air through the fuel line, then slowly move the floats up with your finger, somewhere your ability to blow air will be shut off. Get a ruler and make a little gauge to indicate the preferred heighth (14mm) out of like card board or something, place the gauge up on the smooth surface where the float bowl seats, now repeat the air test and see if it is in adjustment, if not adjust the float level by carefully bending the float tang.

Clean the carb and make sure all the jets are free of obstruction.

Next, get a 15mm piece of transparent fuel line that will slide over the pilot jet. Your local bike shop will have it. Take your pilot with you and make sure it's a good fit. Safety wire it 10mm onto the PJ. That will help deliver a more consistent flow of fuel while ripping over rough terrain. Put everything back together and make sure the little white anti-slosh baffle stays in place, actually it should fit nice and semi-snug with the fuel line in place.

Make sure the filter screen on the fuel petcock is clean. Take it off and turn the valve both "on" and "reserve" while blowing air into the metal exit hole using an air compressor. Gently brush the screen with a soft tooth brush. Blow with the air compressor again and make sure the tank is clean before you reassemble.

Fill up with fresh 92 octane fuel.

Set the fuel screw about 1/8 to 1/4 turn past max idle.

Set idle about 1500 RPM.

If it still does it then it's probably electrical.

Also, make sure your valves clearences are adjusted properly.

Let us know how you make out.


You might want to try this trick that was taught to me . Its the only complaint I have for the XR's. (1) Start your bike as normal let it idle

(2) Take the throttle and give it a quick twist as fast as you can twist.

(3) 9 times out of 10 this can kill an XR dead in its tracks

Maybe during your riding at times of shifting you might be doing this same thing, A buddy said it as stated above was due to the amount of fuel in the float bowl.

as a rule of thumb most XR carburators run very well when the float is parallell to the edge of the bowl housing,

flip the carb upside down , make the float // to the edge by slowly prying the tab which is near the needle valve, go slow , the plastic gets stressed and you could break the tab.

You can pry it with a sm screwdriver


Bass Mechanic,

I just rode this weekend and had the same problem. Most of the day was spent trail riding on very rough terrain with no problems of any kind, only when I was hill climbing. I would make my approach in 2nd gear and it would die as I rolled on the throttle. I tried to ease the throttle but when I would start up the incline, the engine would die just like you were hitting the kill switch.

I have a 2002 XR250 purchased from the original owner who rode it very little, so it sat for a long time. This weekend ride was the first time I had it out for a good ride.

I'm going to start with a good carburetor cleaning, but anything you find would be helpful.

i am seriously considering the edelbrock carb. from the sounds of it there is a proformance gain, and some reports i think were on the XR400 but they claimed somthing like 5 hp. my guess is when have about 25 hp to begin with 5 hp should be a notable improvement.

Check the gas cap, make sure its venting properly. I had a similar situation with my TT-R 250 it ended up being a bad gas cap

i am certain it is not the gas cap as i have in the past drained the tank for winter by blowing through that breather tube to force the gas out of the tank a little faster and into a spare gascan.

i am beginning to think it has more to do with the float lever and the fact the carb does not have an anti slosh material at the bottom of the float bowl. i think that plastic thingy at the end of the main jet on the stock carb is supposed to help with that but it does a poor job.

i havnt had the time to take the carb out and play with it yet so i am not entirely sure what the deal is. i wish they put a window on the float bowl so you couls get a better idea whats going inside

as dr_drz stated, make sure that the coil has a good metal-to-metal ground to the frame, a loose or corroded coil mount will cause intermittent spark. Also check and make sure the spark plug boot is not worn out, and that there are plenty of wire strands making good contact inside the plug boot.

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