I just bought a 2000 XR50R. It is uncorked (although I haven't checked everything myself), has a White Brother E-series pipe, Uni air filter, and came with 175 main and 65s pilot jets. The previous owner lived at about 700' and I brought it down to sea level...no big change.
THE PROBLEM: I took it up to the Sierras to an area at about 7000' and planned to ride anywhere from 5500' to 9700'. The motorcycle shop guy said to re-jet for that altitude and sold me a 172 main and 62 pilot jet which I installed when I got there. I did not run the bike a significant distance at altitude with the original jets, but after making the change the bike ran well (at first) so I though everything was fine. Long story short...the bike seems to bog in fifth gear and especially when I'm letting the bike brake itself going downhill. I can run through the gears pretty well, acceleration seems good, but when I get halfway through fifth, the bike starts to stutter and then will continue that symptom as I downshift through the gears and then (most times) will die when I stop instead of idle. I can re-start the bike right away within 3 kicks and then I'm good again for a couple miles. Like I said, the problem seems most noticeable when going downhill, uphill it generally runs strong. When it is bogging/stuttering/ whatever, my buddy (who was riding behind me most of the time) said he smelled gas. (he was using the same premium gas in his 2001 XR650R with no problems) The bike also begins to backfire a lot when these symptoms occur. I'm holding myself back from really ripping into the thing because I think its gotta be a fairly simple fix that I haven't thought of or got to yet. I should mention that I'm the 3rd owner, the bike only had about 2000 miles on it when I got it, and had been stored for a while. I have put about 300 miles on it since and it has gotten me home every time but is running like crap. Help, this thing is barely broken in and I have miles and miles to go before I sleep!

Sounds like your main jet might be a size too big for that altitude. Easy enough to try a smaller one.

Yup, from the sounds of the symptoms (smell of gas, bogging, etc.) it's running rich. :cheers:

Old Dog, does it make sense that the bike would be bogging at altitude and sea level? Do you think the 175 main (had a 172 in at altitude, now 175 at sea level) that I put back in the bike is too big?

make sure the airbox is truely uncorked, airfilter clean and not over oiled :thumbsup:

u may consider "opening up" the side cover...don't imagine ur do'n to many deep water crossings :smirk:

also check/adjust ur fuel screw for altitude and make sure the ACV is operational :thumbsup:

i wud try the stock 65s/172 at altitude and 68s/175 nearer sealevel before i wud go smaller on the jetting.


:cheers:


P.S. with a few tools u can change ur main jet in the field by rotating the carb and removing the jet access plug on the bottom of the bowl.

P.S.S. maybe check ur float level too...

PeteMc said:

It could be, but as Kenzo said I'd also make sure your air filter is clean and not over-oiled. I'd also make sure your petcock fuel filter screen is clean as well as your tank ... you might have some crud floating around in the fuel system that's clogging things up and/or some bad gas.

One quick way to check to see if it's running rich is to take the air filter side cover off and take it for a rip, if the symptoms lessen or go away, then it's definitely running rich. :cheers:

I live at altitude (7400+ ft) and 90% ride between 6000 and 10,500ft. My bike is uncorked, and the jetting I use is:

165 main
68s pilot
B53E needle with clip in 3rd position

Runs great even to 12,000 ft. :thumbsup:

Thanks for the advice everyone. I'm setting aside some time in the next week to solve this problem as well as personalize the bike a little with some new pegs and bars. I'll let you know how it goes.

Let me know what you come up with, PeteMc. I'm having the same problem with an 05 XR650L that's uncorked and running rich in the Sierras between 5k and 8k feet.