Which spark plugs do NOT have the little screw-on tops that the spark plug wire connects to? Have noticed that when my bike starts popping back through the carb, there is usually 1 or 2 loose spark plug tops.

 

Put a dab of locktite on the screw on caps before installing the plug, no more issues.

 

Does that effect spark conductivity?

 

Nope, just a small amount on the threads. I never had any issue. A very small amount of Locktite is all you need to lock it in place.

 

How many plugs do you have on your bike? Mine only has 2.

 

Alright.... 1 or both.

 

I didn't think the HD plugs had the screw-on tops do they? I know the Autolite ones that I use have them.

 

Some have four, such as S/E Dual-Plug High-Compression Heads, and the Sportster Sport model came from the factory with dual plug heads.

 

Road Dawg is right, the stock plugs do not have a screw on tip.

If you tighten the screw on tip with a pair of pliers before you install the plugs, you will end your problems as well. It is hard to over tighten if you are holding the plug with your bare hand. I think that the manufacturers of these plugs ship them loose, so that, the installer can quickly go either way.

 

+1 for the tighten them up with pliers - NO loctite (it can/does cause connectivity problems)