Most of the time my 93 Heritage runs fine but sometimes as I try to give it gas it will miss and backfire but still idle ok. Also it fouls the rear plug and if i change the plug all is ok again.
Any ideas i.e. leads,coil etc

cheers Popeye

 

If it's just the rear plug and happens to the new plug you install, I would suspect the plug wire as it is associated with only that cylinder. Also inspect ths coil around the rear plug wire turret for any cracking or carbon tracking. Is it gas fouled or oil fouled?

 

I would do a compression check on both cylinders. They should be within 5/7 pounds of each other. Check this and let us know what it is.

John TN

 

Pretty sure its oil fouled and as far as compression goes i redid the top end a year and a half ago. As I say its not constant and when I change the plug its good for a least a few days to a week Popeye

 

I still suggest checking the compression, you can have good one day, bad the next minute.

John TN

 

Sounds like you may have a ring or valve seal problem there. Try a compression test on that cylinder , then add about an ounce of motor oil to that cylinder and try it again. It will come up just a bit with just the oil, but if it comes up significantly, you have a ring problem, if not maybe a valve seal problem sucking the oil into the cylinder.

 

I agree with TCSTD's procedure, let us know what you come up with. Look in the DIY section for a complete step by step on compression testing.

John TN

 

Thanks guys I found the problem A leaking rear head gasket. But it only farts when the bike is cold. When it warms up and the motor expands it seals and no more problem. I will redo the top end next winter. Cheers Popeye

 

>>>But it only farts when the bike is cold

When it warms up the cylinders expand more than the studs which are steel so it seals, sounds like somethings warped or loose