1988 sportster 883 converted to 1200. I went to start it today. Closed the choke partway like always. Engine started but lacked power. I rode around the block a couple times.

I then checked the spark plugs. The first thing I noticed was that the outside of the rear cylinder was much cooler than the front. The front plug looked like it should but the rear plug looked black and wet. I should have checked for gas smell or if the residue was oily but I didn't. I cleaned the rear plug and put it back in. Started the engine and the bike ran fine.

So, I need to do more checking but I just wanted to see if anyone has any initial thoughts or theories. Any ideas about what else I should check? I suppose a compression test would be a good idea. I tried to check the compression the other day but my tester did not have an adapter for 1/2 inch plugs so I need to find one.

 

Do you start it and let it run for short periods of time often? Reason I ask is last winter I would move my bike in and out of the shop daily so i could work in the shop and it fouled my rear plug, plugs were fairly new but I changed the plugs, it ran fine and I started pushing it in and out instead of starting it to move it 100ft. Havent had a problem since

 

That's a good point. I have been working on the forks the last couple of days and I have been starting it up without running it. I'll try taking a couple longer rides and see if that changes. I still think I will check my compression anyway. I was going to check it before but didn't have the adapter then I kind of forgot about it. Too many other things to work on I guess.

 

Check your plug wires, are they seated properly? Check for corrosion at the coil terminals too. Sounds like something simple.

John