xr 80 heads ...Are they different?

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#1
I picked up an 86 xr 80 that is hard to start and ugly (the price was right at 150) The head is a different color than the engine, telling me it is from a different year. ( the head is not painted and the engine is black) Could this be the source of the hard to start problem? Were any of these heads different? Would an xr75 head fit?
 

CRGuy

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#2
The xr75 head won't fit. The hard to start problem is probaly in your carb. You can put a 02 head on the 80 and it will work. If you want I thing you can buy a 100 head and piston and that might fit.
CRG
 

Mark C.

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#3
My old '77 XR75 head is the same exact head that's on my friend's '80 XR80 in my shed. I'm not quite sure a XR100 piston will fit in a XR80 cylinder, But a XR100 topend might fit on a XR80 motor :think
 

Mark C.

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#4
Hard starting

Also for the hard starting describe more to us. Does it have the 3 simple things like compression~>spark~>fuel?

Post back with answers please :)
 

ACS

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#5
Crummy running on a old XR generally means that the carb is dirty and the points are in need of replacement or adjuctment.

The heads on the later XR75's are same as XR80's right through. First XR's engines were silver then black then silver. Early XR75's have different cam tower. A XR 100 head is a bolt on swap onto the XR80 and you get bigger fins and bigger ports esp the intake but combustion chamber is bigger and compression is lower. Raising the comp by machining the head can mean the cam chain is too long. You cannot fit a XR100 piston in a 80 as the wrist pin is bigger in the 100 by 1mm. You would have to bore the 80 rod which can be a problem with reliability. Best bet is a 95 or if you can find an old 98cc big bore kit. How much do you want to spend? It can make a $150 bike into a $2,000
 

CRGuy

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#7
I meant that the piston and head will go onto the xr80 base.
CRG