right cylinder issues

mr bill · Jul 21, 2020

Got my 1975 XS650B running after years of sitting. I had a bike shop set the timing and balance the carbs. It was running great then the right side started to backfire when decelerating and the idle dropped off. Prior to starting both carbs were off and cleaned and the gas tank has been totally cleaned out. It starts easily but trying the "dead cylinder" approach that right side will not run by itself it dies immediately. I've also noticed the exhaust on that side seems cooler than the left. It's got new plugs and good white spark to each. I've replaced the condensers and no change to the way it runs. I thought I'd ask for opinions before doing anything else.

Jim · Jul 21, 2020

If it's got good spark and the left is running normally I'd suspect the idle/pilot circuit in the carb has trash in it. But, first things first... make sure ignition is good on that side... timing could have slipped. What kind if ignition are you running, points... Pamco... other?

gggGary · Jul 21, 2020

make it idle for a bit pull offending plug, wet or dry?
Try seat and reset idle screw, Condensers so I'm guessing points.

Jim · Jul 21, 2020

gggGary said:
Condensers so I'm guessing points.

Yeah.... missed that part...

mr bill · Jul 21, 2020

Jim said:
If it's got good spark and the left is running normally I'd suspect the idle/pilot circuit in the carb has trash in it. But, first things first... make sure ignition is good on that side... timing could have slipped. What kind if ignition are you running, points... Pamco... other?

I'm running stock points ignition. I've had that carb off already and removed the idle jet and blew it out with carb cleaner. Also removed the idle mix screw and blew that out. I also suspect the timing for that side slipped because the points are not opening when the mark on the flywheel is in that space where the "F" is.

mr bill · Jul 21, 2020

gggGary said:
make it idle for a bit pull offending plug, wet or dry?
Try seat and reset idle screw, Condensers so I'm guessing points.

I've already done that to the idle screw and shot some carb cleaner in the hole. That side still won't run by itself. Haven't put new points in yet.

bosco659 · Jul 21, 2020

I went through the same ordeal but I’m running a Pamco ignition. Turned out contamination in the tank was causing blockage of the orifices in the pilot jet. Thorough cleaning and good filters seems to have cleared up that problem.
If the cylinder is not running because it’s too lean, can you get it to run by pulling the choke? Another member suggested spraying a bit of starter fluid down the problem carb to see if that gets it to run. That can help determine if it’s a fuel or spark issue.

David Toll · Jul 22, 2020

Had that problem on my SE. The guy who finish tuned it said that it was cheap Chinese points -unfortunately the brand Mikes sells. Replacing them with Yamaha points seemed to cure it although the right is still not quite as strong as the left.

bikefreakjon · Jul 22, 2020

You said it had spark.
Recheck the timing and point gap, if that doesn't work.
It's the carb dude, clean it again. Only better!

5twins · Jul 23, 2020

You said you cleaned the pilot jet and the mix screw hole, but there are 3 more small holes going into the main bore that deliver the pilot jet's air/fuel mix. If they're blocked then you would only be getting a very small amount of that fuel mix .....

The pilot jet delivers it's fuel mix up into the carb through the small hole marked below .....

Dribble some carb cleaner into it and blow it through using compressed air while blocking off the mix screw inlet and the outer hole the mix screw screws into. That will direct all the air pressure out those 3 holes. You can also blow carb cleaner in through the mix screw hole while blocking it's inlet and the hole on the bottom of the carb. Again, this will direct all the air pressure out those 3 holes.

mr bill · Jul 24, 2020

5twins said:
You said you cleaned the pilot jet and the mix screw hole, but there are 3 more small holes going into the main bore that deliver the pilot jet's air/fuel mix. If they're blocked then you would only be getting a very small amount of that fuel mix .....

The pilot jet delivers it's fuel mix up into the carb through the small hole marked below .....

Dribble some carb cleaner into it and blow it through using compressed air while blocking off the mix screw inlet and the outer hole the mix screw screws into. That will direct all the air pressure out those 3 holes. You can also blow carb cleaner in through the mix screw hole while blocking it's inlet and the hole on the bottom of the carb. Again, this will direct all the air pressure out those 3 holes.

mr bill · Jul 24, 2020

Thanks for the pictures. I didn't know those 3 little holes existed. I'll pull the carb off and clean again.

5twins · Jul 24, 2020

You'll have to flip the butterfly plate open to see them. It blocks them from view when closed.

mr bill · Jul 26, 2020

5twins said:
You'll have to flip the butterfly plate open to see them. It blocks them from view when closed.

That was it! Followed your instructions and the right side is now idling by itself. I was then able to balance the carbs. Took it out for a ride and it ran great. Thank you.

Boog · Jul 26, 2020

mr bill said:
That was it! Followed your instructions and the right side is now idling by itself. I was then able to balance the carbs. Took it out for a ride and it ran great. Thank you.

Oh how I love a happy ending...

right cylinder issues

mr bill

XS650 Member

Jim

Beyond the edge is the unknown. Here be Dragons

gggGary

If not now, When?

Jim

Beyond the edge is the unknown. Here be Dragons

mr bill

XS650 Member

mr bill

XS650 Member

bosco659

XS650 Guru

David Toll

Reliving my youth?

bikefreakjon

XS650 Addict

5twins

XS650 Guru

mr bill

XS650 Member

mr bill

XS650 Member

5twins

XS650 Guru

mr bill

XS650 Member

Boog

Traveling Stroyteller

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