2001 road king is only firing on back cylinder. replaced plugs and coil still the same, what is next?

SOURCE: my front cylinder is not firing. I replaced plugs

hi you must check compression first should be same as other cyl. if not check for tight tappet if ok is the plug sparking if you hold it against cyl and turn over motor if good spark put it back and turn over motor few times then remove it and see if its wet with fuel if its not could be carby blocked jet

SOURCE: The spark plug is only firing on the rear

Swap the spark plug wires and see it the moves from the front cylinder to the rear cylinder. Your Sportster should have what is known as a "dual fire" ignition system. This means that both spark plugs fire every time the piston comes to top dead center whether the cylinder is on the compression stroke or the exhaust stroke. This causes what is known as a "wasted spark", the spark plug fires on the exhaust stroke. I don't have any experience with bikes made after year model 2000. Most of these bikes are equipped with electronic engine controls that I don't care to learn about. I work on bikes made in 1999 or earlier. I feel pretty confident that Harley still uses the "dual fire" ignition but I'm not sure if they have any other sensors on the bike that would cause the problem you have. Try what I suggested and it may give you a clue as to the problem. Other than that, I have no other suggestions. Sorry I couldn't do more.

Good luck
Steve

SOURCE: I have a 1991 FXR Super Glide with a front

You need to run a compression test on the engine. The cylinder pressure should be around a hundred pounds or more. There should be no more than 10% difference between the cylinders. If the compression is low enough to cause it not to fire, you probably have a blown head gasket.

You didn't mention what kind of igntion system you have in the bike. If you have the original ignition system, it's a dual fire system and both spark plugs fire at the same time every time the pistons come up to top dead center. This means that one cylinder fires on the exhaust stroke and this is called a "wasted spark" system. Harley has used this type of ignition for almost all their Bit Twins and Sportsters for many years. If your bike has an after market single fire ignition system, the ignition system could be bad causing the missfire. In this case, you would have an aftermarket coil as well with three primary connections on it.

Good Luck
Steve