I'm about to shoot an XR100

HiG4s

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#1
OK I'm lost completly on this stupid bike.

A couple weeks ago it wouldn't run above idle and it fouled a plug.
I put in a new plug and cleaned the carb. After that is ran OK. Since it has fouled a couple more plugs. But after changing them it was OK. Last Tuesday it again would not run above an idle, giving it any gas it would stall. If I put the choke on it will rev some, but still not well.
I cleaned the air filter, put in another new plug, checked the fuel petcock and it flows fine. I tried running it without air filter, cleaned the carb. cleaned the spark arrestor trap, and adjusted the valves, it still did the same thing. This morning I removed the exhuast and checked to make sure it wasn't blocked and tightened the cam chain tension a half turn, tehn put it back togeather. All of a sudden it started working. My son rode it for about an hour and it worked fine, then it went back to dying when you give it gas??????
 

JuliusPleaser

Too much of a good thing.
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#2
Aim Low

And don't lead it much...
 
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#3
Check the float level, needle and slide. Triple check that you can see a clean hole through both of the jets. On my old 200 after sitting for a long time, I had to clean the carb 3 times before the jet REALLY got clean. Check compression, maybe the rings are blown. Good luck.
 

Sage

dirtbike riding roadracer
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#4
Bad gas? had a cbr600f4 at the shop doing the same thing, turned out it was the gas. (had water in it)
 

weimedog

Damn Yankees
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#5
While your at it, check the points...We have one of those things. When all the typical things don't pan out its the points. Ours has shown that type of behavior. Thought we went around this block on another post...maybe another website.

Ours is a 1989 or 1990. Can't remember the exact year. It has gone funky on us a couple of times. Two times it was those points/timing and one time it was the valve adjustment. Its real easy to adjust both valves and points on those Honda's.

Oh yea one time the petcock got clogged for some reason. It would start OK then as it started running outs gas it would do the expected things.

Points they are so east to check....spend the 15 minutes.:)
 
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#6
Water in the gas can cause such problems. A drop can get hung up in a jet, cause problems, go away and then come back. On one bike, I flushed the tank and cleaned the carb three times before all was well. The third time I even put some "dry gas" in the tank. there was no reason why water should have gotten into the tank....maybe condensation.
 

Jonny426

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#7
Killer XR...

One more thought, check the fuel flow thru the needle & seat. if some crud makes it by the petcock filter it may restrict fuel into seat.Remove the carb bowl, use a catch can ,and turn on the petcock.The seemingly opposite effects of fouling plugs and running the carb dry make me think crud is lodged just above your needle seat. good luck ,Jonny 426. (If you do take Julius Pleaser's advice,I like #00 buck thru the 12GA.)
 
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#8
Check the timing and I think your probably running too lean. When I start my bike, I can't touch the throttle until the engine is warm, otherwise it stalls.
 

KWJams

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#9
Where the heck is XRpredator??

:)
He can tell you just what caliber and grain it would take to bring one of them suckr's down. ;)
 
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#10
jets!

It really sounds like you high speed jet is completely plugged and your low speed jet is damn near completely plugged. Remove them and clean them. I used a single wire strand from a wire brush I had. Hold them up to the sky and make sure they are free of blockage.
 
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#11
Something else to think about.

HiG4s.

If your carb checks out ok, sounds like you may have some problems with your cam bearings. I have seen this happen on several XRs. The camshaft on some XRs runs on a plain aluminum bearing on one side and a ball bearing on the other. I can't remember if the XR100 is like that or not, but, what happens is, the aluminum bearing surface can become worn allowing the cam to move around.

Since the points are located on the end of the cam, the gap can be affected if the cam moves. In other words, if the points have .016 clearance and the cam bearing surface is worn, allowing the cam to move more than .016, it closes up the point gap at higher RPMs.

The bike may idle ok, but, when you rev the engine, it will allow the cam to float, thus closing up the points. Since you adjusted the cam chain and it runs a little better, it sounds like this could be the problem.

The way to check for this condition is, remove the point cover and valve adjustment caps. Turn the engine over and set it on top dead center on the compression stroke. Both valves should be closed and you should have clearance at both rockers.

Then, take a pair of vice grips and clamp them on the 6mm bolt that holds the point cam on the end of the camshaft and try to move the cam up and down. If you get any movement up and down, your cam bearing surface may be worn out and you will have to remove the top cover for further inspection.

If all else fails, take Mr. Pleasers advise, except if it is not running, you don't have to lead it.

Just my $ .02
 
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HiG4s

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#12
Just to let everyone know, after adjusting everything I could I orderd new jets, I haven't even put the main in as after I replaced the pilot it started running fine.
Oh, and being a 96 it doesn't have points, all electronic.