will a bad plug work good at idle but not perform at its best at higher speed.Bike vibrates at higher rpms but it feel like when a plug is not firing right.Would this bike run if one plug was not firing at higher rpm or is that possible.Dont know much about plugs so is it possible for a plug to fire good at loww rpms and act up at higher i guess is what i want to know

 

Plugs can do so funny things, had a mates bike playing up, opened the gap and fixed the problem. You could buy two new plugs this may be an easy solution. My Piper Tomahalk was running rough when doing pre flight magneto checks, after a weeks investigation found a crack in the distributor cap. I picked it up but my wife has been flying with virtually one magneto. Moral of the stroy is the problem may not be plug related.

Good luck in finding the problem.
Frook, 883 Sportster, New South Wales, Australia.

 

I would just pick up a set of new plugs. The HD plug is a Champion RA8HC. They are about $1.50 ea. at most auto parts stores. Even if they don't fix the problem, for $3 you've eliminated that possibility.

Edited: The HD plug you buy from the Harley stealer is a RA8HC made by Champion with the HD Logo painted on it.

 

..when I got my Sporty the P/Owner had swapped in some Champion Plugs (wrong ones naturally) and they were acting up..did not help that he'd also gapped them wrong. Wont hurt,especially if you have some miles on your bike or got it used t, to put in new plugs...and gap them right..should be set at .40. Good Luck

 

well put new plugs and wires but still vibrates out of ideas so off to thre mechanic. have tightened motor mounts checked for intake leak checked primary just plain out off ideas

 

Hope things work out for you. Let us know the out come...

 

rechecked new wires to make sure they where connected right and found a ground wire that was not tight so tightened it up and vibe was gone.I guess at higher rpm it wasnt making a good ground so wasnt getting good spark at higher rpm but one plug wasnt the best and one wire wasnt the best. so maybe a combination of the three was the culprit but anyway good to go and thanks for all the replies