I have a 1981 Sporster. My front cylinder is not always firing. I have been told that the plug keeps getting fouled. I am not sure that is the case.

When I start the bike on one the back cylinder and carefully hold the spark plug wire next to the spark plug I can see the spark jumping to the plug and the the cylinder begins to fire. BUT, when I securely plug the wire onto the spark plug the cylinder stops firing.

Can anybody provide me any insight? thanks

 

Just for starters, have you replaced the plugs and gapped them properly" What is the condition of the front plug" What color is the electrode? Is it fouled?

 

These are new spark plugs and have been gapped based on the specs in my manual. The plug does not seem to be fouled.

How come when I hold the spark plug wire a few centimeters away from the plug the spark arches to the plug and cylinder fires, but when I put the spark plug wire securely on the spark plug the cylinder does nothing?

Thanks for you help!