I been riding this WG for 3 years. Twice in that time it has done this weird drop cylinder thing at speed. It only happened for a moment and was good after that. The last time I talked to an indy shop that told me to put an inline fuel filter on it. Did that a year ago and it's been running like a top ever since.

When I added the filter I also changed to factory plugs and did a compression test. Had 135 in front and 105 dry/115 wet in the rear. So I figured ok I have an issue in the rear and I'll just keep an eye and ear on it. No problem since and been on a few long rides trouble free.

Yesterday heading out on the freeway at 80 it's running great and all of a sudden drops a cylinder again and it doesn't go away. Got off and it was definitely running on one cylinder. The guy behind me heard it go away too. Since I thought I had rear cylinder issues and it did the same thing on restart I just called a tow. I figured it stuck a valve or something and didn't want to risk more damage by riding it home.

I pulled the plugs-no obvious damage or issue there, did a compression test expecting to find zero in the rear. 130#. I must have messed up the last time cause now it's 135# front, 130# rear. That's ok too. Pulled the fuel filter, clean. A stuck valve, broken rocker, or flat cam would in make some noise I would think. Nothing like that happened, no noise, pop, sputter or anything. It's just like I flipped a switch and turned of one hole.

So now what? Bought new SE plugs and wires, put them on, it runs just like it should again.

Any thoughts, ideas, clues, anything? I don't know what the heck it is and am not sure what to look for now.

 

The only time I have seen that kind of thing happen is when something is wrong in the ignition. Could be old spark plug wires. They do go bad by the way. They start leaking. Bad plugs. Use OEM plugs. Or a faulty coil. Every once in a while a fouled plug will cause the same thing. Yours don't look fouled. Forget the compression tests. So replace plug wires and plugs and see what happens.

 

You are probably aware of this, but the cable that plugs into the throttle body has had issues that causes this same event. This is on the newer models. What year we talking about? If it is the 94 model, you can delete my post.

 

Plug wires or coil is losing one side , swap the wires around and see if the miss moves . From the picture I'm guessing the first plug is from the rear ? Timing can cause the electrode to crude up like that also but rears have always had a tendency to do that and our crappy gas here in CA doesn't help it . From the picture it looks like a chunk of crude broke loose and shorted the plug on you maybe .

 

The plug on the left is the front.

I put a new OEM coil on last year. Would a stock coil lose only one side? It did this with the old one but it was momentary, it lit back up before I time to stop and analyze it.

The wires were Drag Specialties from 3 years ago. I dissected the rear one last night, nothing obvious wrong with it. I rode it this morning with the new SE plugs and wires about 60 miles and ran like a champ. Bought some extra new plugs for spares and if it happens again I'll pull the wires one at a time while it's running.

Thanks all of you for the input Lot's of smart folks on this board.

 

Front plug keeps looking like that you're looking at a valve job in a few years , I'd wait till it started giving you trouble .

 

Thanks. Got a good cylinder head guy in Palm Springs. He'll take care of that when the time comes.

 

If it's an EFI bike I'd be checking the injector wires before going any further.

Some bikes had wire "chaffing" due to wire routing and/or tie straps being the culprit.

I've also had two ECM's go bad before and both had different symptoms but neither lost only one cylinder.

 

It's carbureted, no efi or ecm's to deal with but wires to the coil and ignition box could be worth checking.

 

Timing, fuel, fire, and compression. Looking at the plug, I would figure plug wire or plug or both.