I HAVE A 1990 SPORTSTER 883 FITTED WITH 1200 BARRELS ETC.
SHE HAS BEEN LAYED UP FOR A MONTH.
NOW SHE ONLY RUNS ON ONE CYLINDER,THE REAR ONE IS SPARKING BUT NOT RUNNING.
I HAVE BEEN TOLD BY A MATE THAT THE UNLEADED FUEL CAUSES THE VALVES TO STICK AND THAT I SHOULD JUST RUN IT AROUND UNTILL IT CLEARS. CAN ANYONE OFFER ME SOME ADVICE HERE?
CHEERS DON.

 

compression check!

 

Just do a qwik check, switch plugs. First things first. Look at 'em good B4 you put them back in.
The gas won't stick your valves, but it will gum up your system real good.
Without seeing it or hearing it, ????. Month shouldn't do it, tho.
Put some Seafoam or Gunk Fuel Injector cleaner in the gas. DON'T over do it. "Mo' is NOT always betta."
BUT verify you do indeed have spark and good plugs. Then you can go from there. Like I said, first things first, do the simple, qwik checks first. Course, you could tear the cam chest open and look for a broken camshaft, and THEN check the plugs, wires, compression, etc. However you wanna proceed.

 

Maybe you got some water in the fuel,you do have fuel don't you?

 

Yeah a month shouldn't cause the damage you're describing. The first thing to gum up would be your carb and since the front is firing, we know you at least are getting fuel there.

I'd say check compression first, just not acurately. You can do it without a gauge pretty easy, just put it on a lift, pull both plugs, put it in gear, put your thumb over the plug hole in the back jug and spin the wheel through a cycle. If you feel the air pushing your thumb off the hole or pulling your thumb in, that should be enough to fire.

Also, pull both plugs and turn the bike over. In a few rotations you should see fuel start dribbling out of the plug hole. That can at least verify that fuel is getting to the back jug, but since it's a carb bike that should be happening if the front is so the odds are low that fuel delivery is the source of the problem.

 

Will the bike run better when it's upside down?

 

You'll wanna pull the engine first. I makes it a lot easier to split the cases to see if the rods are still connected to the crank.

 

Okay Mr. Wiseacre! Turn the motor over (with the starter!, since you can't get away with anything on this forum!).

 

Ahhhhhh.... Thanks for being a good sport - couldn't resist.

 

Like others have suggested, start simple and go from there. Pull the plug check the gap and if fouled, wet or what ever. I had that problem with my 1996 Buell S2T. It was always the plug and always just the rear cylinder. It would still go 50MPH on just one cylinder...don't ask me how I know........ I often wonder if it was a fixable mechanical flaw and why was it always the rear cylinder? I changed out the plug wires and always started keeping a fresh set of plugs and gapping tool in my bags.