Need some help...

Hey guys, I'm not having luck anywhere else so I though I would post here and see if you all could help. I have my older 87 xr250r. Bike is completely rebuilt with stock jetting. The carb is completely clean and the bike fires on the first or second kick. Now it will run fine until it gets good and warmed up then it misses in the midrange only. The second you get anywhere from 1/4 to 3/4 throttle it misses and sputters until you hold it wide open and it clears out. All jets are clean, motor is mint, and the airfilter is clean. It will run fine until it warms up. Anyone have any suggestions? Bad coil, CDI, stator?? I've dumped enough money into this thing to buy a newer bike. I'd just like to fix this issue and ride her.

Does the carb on this older XR have a jet needle or some other adjustable midrange fuel mixture control?

Yes it's your standard XR Keihin carb. Pilot is a 40 and main is a 125. Clip and needle are stock. It's only sputtering when warm. It starts first kick and the choke is not needed at all after it fires. It's got the snorkel pulled, uni filter, and baffle pulled.

have you check the fuel tank screen? It sounds like fuel starvation?

Does the slide move smoothly when you twist the throttle. Observe by removing the air boot and having someone open the throttle slowly.

The slide moves fine. All indications point to a needle/clip issue. However it is stock. I would assume it would run crisp, yet hot if it were lean not sputtering and breaking up?

If the needle jet and jet needle are original equipment it is possible that over time the seating has changed the shape of one or the other. I would order a new set and see if that helps.

Thanks I'll give it a try!

Sounds like your running rich on the needle.

The clip/needle aren't adjustable on that carb? If it's adjustable, raise the clip a notch, lowering the needle.

I assumed that since Tim has cleaned and inspected the carb (slide action, jet sizes, etc) that he's also made adjustments to the needle/clip position and has not had any success. My bad if this is an incorrect assumption. My thinking is to replace an inexpensive part that is suspect.

I've tried up and down on the needle no luck. I'll mess with it this weekend and go from there. We'll see. Thanks for the suggestions! :cry:

My 86 XR200 (I know they are different) did that among other things...So I don't know exactly what caused it but here are something that may or may not cause that but one thing that stumped me a few times.

I had to replace the CDI pickup (the one that is around the Cam end) once because of similar symptoms (I don't remember if it was only warm or not)

A time before that the CDI pickup got loose and rotated slightly so the timing was a little off...but that doesn't sounds like something that would only affect a warm bike either?

This is stumping...I'll keep thinking b/c that sounds like similar to me once when I was trying to sell the bike but I don't remember what fixed it?

(It was the first bike I worked on myself so I messed with everything so if something went wrong I had a ton of things to check that I had messed with previously!)

I'll keep thinking.

I messed with timing, fuel-Float position, Slide position; took apart the carb many times, once vacuum in the tank caused the same thing...

I'll keep thinking.

JT

Hows the valve lash???? :cry:

I assumed that since Tim has cleaned and inspected the carb (slide action, jet sizes, etc) that he's also made adjustments to the needle/clip position and has not had any success. My bad if this is an incorrect assumption. My thinking is to replace an inexpensive part that is suspect.

I wasn't trying to contradict your diagnosis, but troubleshooting via a tv screen is limited, at best. The more questions asked, the more info recieved.

When a bike runs rich, due to elev. changes, different airfilter oil, etc. or whatever, the needle ( 1/4 to 3/4 throttle ), usually pops it's ugly head first, displaying above symptoms discribed.

Let us know what's up!

UPDATE: I hopped on her to take a bolt off for the pig and figured I'd fire her up and see how it runs. Spent a half hour on the bike and it had no issues?? I found this weird and was wondering if a bike can sputter like that during break-in and when the rings finally seat, will it run mint like it was yesterday??

Tim,

I recently had some engine work done on a 2 stroke including a fresh top end. I did not experience any break-in sputtering, however I didn't run it hard during the first 30 minutes.

Never look a gift horse in the mouth. Glad the problem seems to have cleared up. Who knows, maybe your air filter simply needed to dry out a little.

Who knows. Funny you mention that. I had a Moose filter in there with the "OEM" backfire screen. I replaced it with a uni and uni backfire cage and never ran her. Started it Saturday and she ran mint. Maybe I was choking her of air when it got warm. And when it was cold it was like the choke was left on due to the old cage(clogged probably)?? Cool None the less...Thanks!

Sometimes when I'm fiddling with my jetting and trying to set it up for a higher elevation, I'll slap the stock filter and screen in to restrict air flow. It kinda gets me in the ballpark...

Stay with one filter & oil, squeeze it the same every time. One less variable to deal with.

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