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Timing Issue on XR100

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I have a question that I'm hoping someone has experienced and can save me some time with diagnosing. I have an '02 XR100R and the spark plug hole stripped out. I found out that the XR80 head would interchange and I had one so I switched the heads. Now I can't seem to get the timing set right. I've moved the chain one link forward from the standard setting and it allows the valve to hit the piston. When I move it back one notch it cuts out and definately acts out of time. With the setting right on is still cuts out but not as bad. Under load it spits and coughs then take holt for just a moment and then starts to cut out again.

My question is can there be something about the XR80 head that would make the timing no be spot on in any position?

thank in advance for any help?

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I will double check to make sure but I am positive that is the case. I had the sprocket removed from the cam shaft on the 80 when I took the head off so I know it was in a different location.

I'm scratching my head now.

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isnt the 80 head shorter then the 100? it has to be something with the cam chain, the chain guides, or the sproket. Count the teeth. 80 sproket has 28t and the 100 is 30t

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80 sprocket is smaller number of teeth I found it out a few weeks ago compare the two and use the larger gear.

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I did not try a new cam chain. I did re-check to make sure I had the 30 tooth cam spocket on the bike and it indeed was. After saying that I found a post on the board noting the differences between an XR80 and an XR100 and it said that the XR100 uses a 15/28 crank/camshaft sprocket and the XR80 uses a 14/30. If this is true then I have the wrong size on the bike. Where might I verify the exact size for the XR100?

Also here is what was said about the head.

i. The cylinder heads are also different, however the XR 80 head can be use on the XR 100 with the XR 100 cams sprocket and vise versa. (The XR 80 cylinder head has smaller intake and exhaust runners. Also a slightly small combustion chamber) the do share the same 22mm intake and 20.5mmexhaust valves.

Could this contribute to the bike's ill running attitude now?

thank you for eveyone's input.

Steve

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xr80r have a 14/28 cam chain gears and the xr100r have a 15/30 gears... the ratio have to be 1:2 ...

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Makes sense!! I have the correct cam sprocket on it.

Does anyone think that the smaller intake and exhaust runners in the head would have a major impact?

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