XR80 runs bad - help

My son has a 2002 XR80R.  It is good condition and appears to have low hours; he has been riding it for two seasons.  It has started to run poorly and I can’t seem to pinpoint what the issue is, if you have any advice please let me know.


  • A few months ago the bike started to idle poorly; it would idle fine then drop 150 – 200 rpm.  I compensated by increasing the idle.  The problem with this is that it idles too high, except for when it drops down.  It will drop down every 60 seconds or so and it will stay low for about 15 seconds then climb back up.  It does not do it when it is cold, only when it is warming up or hot.
  • I just assumed that it needed a carb cleaning, so I took it apart and cleaned it thoroughly.  I put it back together and there was no difference.
  • The bike runs fine otherwise; it revs fine and seems to have no loss in power.  With this in mind I assumed it might be a bad pilot jet, so I bought a new one (same size - which is the same as factory setting).
  • I put the new pilot jet in and there was no difference.
  • Then it started blowing white smoke, it would do it on start-up and during idle, even when it warmed up, but mostly at low RPM.  Right around this time I had just switched to No-Toil, I just assumed that I probably put too much on the air cleaner as I can’t seem to see any oil loss on the dip stick.
  • The current set up is:  Air mixture screw – screwed all the way in.  Idle screw – also screwed all the way in.  It seems a little insane to me that the idle screw would have to all the way in to run.
  • There is only one other piece of info that I should add:  When I cleaned the carb I noticed that the idle circuit seemed to be plugged (I could be wrong, let me explain).  There are two small tubes on the filter side of the carb.  One of the tubes goes to the air mixture screw, then to the pilot jet.  There is a small hole on the engine side of the carb that I feel should be connected to this idle circuit but no matter how much carb cleaner or compressed air I force into it, it just keeps coming back out.  It looks like it should connect to the pilot jet, but nothing goes through.  I have tried pushing safety wire through and it just stops.  Should it be connected?


Your thoughts?  Thanks

Each and every little hole comes out somewhere. Mixture screw should be at 2.5 turns out. Be sure it has a washer, spring and O ring on it.

Idle screw should only be in far enough that it just starts to lift the slide. Look in from the air filter side and see if the slide is all the way down.

Sounds like its running too lean on fuel. Make sure the mixture screw is 2.5 turns out. If that fails, you can go on amazon and get a brand new carburator for 25$

Yes, I was thinking the same (buying a replacement carburetor), are they really only $25?

any idea where the white smoke is coming from?

4strokeridertt, according to this schematic on Bikebandit there is only a spring for the air mixture screw.  Mine does not have a washer and o ring.

With the sporadic idle it sounds like there might be an air leak, which would also make it hard to fine-tune the carburetor. To test for this, spray carb cleaner around the intake with the bike running. If the idle changes there is an air leak.

The white smoke could be a sign of worn rings.

Edited by GrimReaper_503

ok, I will give this a try

I bought a Chinese carburetor from Amazon; it was $19!  I installed and it runs much better.  There is a bog in the mid range but I think if I raise the needle I should be fine.  The white smoke seems to be almost gone (maybe my imagination). 


i am still baffled as to why the little hole on the engine side of the carb is blocked, I am convinced that this why the other carb ran so poorly.  Has anyone ever heard of this?  I tried cleaning it with carb cleaner, compressed air, soaking it for a few hours, I even tried steel wire, the obstruction won't budge.


Thanks for the advice

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