81' xs only running on right cylander

[johnlaw]

I have been working on an 81 650, on start up the left pipe blows grey smoke that clears up pretty quick. I only got to take one trip for about 3 miles. It ran great for a moment then I could tell it was only running on the right side. A couple times at mid throttle the left side came back to life and then nothing. When I pulled the plugs the right one was black, and the left one was wet, but looked almost new. Both sides are getting spark, and both sides were at 150 psi when I did a compression check. I rebuilt and re jetted the carbs for pipes and pods. I checked the voltage after installing a new battery. 12v at idle 14v while reved up.

After ruling out spark, compression, and the charging system, I tore the left carb back apart and cleaned it again. After re installing and topping of with some premium fuel, I fired her back up. More smoke from the left pipe, and a lot of spitting and sputtering, and backfiring, it seemed to clear up. I only got to run it up and down the driveway a few times, and the warden said it was time for supper.

I hope it is cleared up otherwise I don't know what else to check.

 

[Patches]

Have you tried swapping plugs/wires to see if it changes cylinders? I had the same problem. Still got spark, but apparently the plug was still bad. Realized this by swapping plugs and having the dead cylinder move from the right to the left.

 

[xjwmx]

My '81 has started running on one cylinder three times. In every case it was a leaking inlet valve on the carb causing the carb to flood or run way too rich. My carb passages are real clean though. Dirty passages could also cause it.

 

[johnlaw]

After cleaning the carbs for a second time it is running like a champ.

 

[xjwmx]

Yo yo yo. Anything that happens to one cyl only is pretty likely to be the carb. Doesn't have to be, but is most likely. And if it's the carb, the most likely thing is dirty.

 

[tadd442]

After cleaning the carbs for a second time it is running like a champ.

It's probably the owner....

 

[johnlaw]

It's probably the owner....

waka waka

 

[johnlaw]

acting up again and no 4th gear..........good lord I think this is going to get expensive!

 

[tadd442]

I may have transmission parts later this week, as for the carbs, have you replaced the needles & seats?

 

[XSJoel]

I had the same thing when I went look at my 1981 XS650. The PO thought it was a spark issue, replaced the coil and everything. I have an extra coil to prove it. Took it to my guy, he did a bunch of maintenance stuff and cleaned the carbs, ran alright. Sat for a while and got gummed up. Me and the dad tore it down, found the in tank filter had come off and the tank had sediment in the tank that made its way into the carbs. We just got it all back together and rejetted, runs pretty good, just got a charging system issue, needs to be rejetted and shakes a bit at speed. Glad yours is running like a champ, can't wait to be able to say the same.

 

[johnlaw]

A quick blow out with the air compressor seems to fix it every time. I am going to clean out the tank and get a better inline filter and hopefully that keeps it from re occurring.

But then again, if that is the problem, why does it only happen to the left cylinder?

 

[johnlaw]

yup new needles and seats

 

[tadd442]

A quick blow out with the air compressor seems to fix it every time. I am going to clean out the tank and get a better inline filter and hopefully that keeps it from re occurring.

But then again, if that is the problem, why does it only happen to the left cylinder?

Maybe the left carb isn't as clean internally as the right one. As you are experiencing, they are pretty sensitive S.O.B.'s

 

[XSLeo]

When on the side stand the left carb is the low one. More likely to develope trouble. As they say sh*t runs down hill.

 

[pamcopete]

The left cylinder is also the one that provides vacuum for the pet cock, so if there is a leak in the vacuum diaphragm of the pet cock, it will only affect the left cylinder.

That would also explain the wet plug on the left side if it is sucking in raw gas through the pet cock diaphragm.

To test for this possibility, remove the vacuum line to the pet cock and plug the vacuum barb with a blind plug. Open the pet cock to the prime position and take her for a ride.

 

[pamcopete]

johnlaw,

Did you get the problem solved? Did you read my brilliant post above?