'81 XS650-SH Left Cylinder Not Firing

[CheckMark]

My 1977 XS650D is giving me a heart ache as it started acting up on my way home last night.
After topping my tank I went over to get an oil change. Shop said that they were booked for the day but had room the next. I have a clutch cover that is cracked and they can repair the crack. So I started the bike up with a couple of kick starts and rode over to a local diner, parked, went in and ate. After I finished eating I went out and had a difficult time getting her to start. Then she finally started but was running on one cylinder. Once under way I stopped at a local BMW shop to see if I could get a couple of plugs but they did not carry NGK B7ES's but I did get a couple at a nearby Schucks. After I pulled the plugs I found the left one fouled so I replaced both as a set together. After getting the 650 started again she was still running on one cylinder. She ran like that all the way home. But occasionally when the motor gained rpm's she would act like the missing cylinder wanted to fire again. A few days before this bike would stumble at the higher end of the rpm range.

Where should I look first points, fuel or somewhere else?

 

[CheckMark]

I am wondering if what mine was doing last night might be similar to this?

 

[minnesota mike]

CheckMark, I would definitely look at the carbs first. What I've found (even more recently than in this thread) is that there is oil vapor coming from the breather hose (the one that connects from the valve cover to the bottom of the air filter assembly, assuming your '77 is the same in this respect). This oil might tend to pool on the left side when the bike is idling on the kickstand, and somehow over time it plugs up the air jets - not the fuel jets - on the left carb ONLY. This has happened twice now, and I'm in the process of rerouting the breather hose to have its own air filter.

This would explain the fouling of the left plug (running rich), and the intermittent firing that you and I have both experienced.

It's just a hypothesis right now, so we'll see!

 

[CheckMark]

minnesota Mike I must say your spot on when you said "look at carbs". I went out and put her up on the center stand, popped plug cable off the plug that did not seem to be firing and on to one I had in pocket. Then I pulled the points cover off and with ignition on blipped the lower point set a couple and watched the plug spark. Then my eye caught the rib of the carb out of the left spigot by almost a half inch. I loosened the clamp and shoved it back in and tightened the clamp back up. replaced the side cover and she kicked right over and ran sweet once more. So the carb coupling prevented a correct fuel/ mixture from being presented for combustion. Thanks Mike

 

[minnesota mike]

I'm glad it was an easier fix than mine!

 

[Daniel Wojahn]

CheckMark, I would definitely look at the carbs first. What I've found (even more recently than in this thread) is that there is oil vapor coming from the breather hose (the one that connects from the valve cover to the bottom of the air filter assembly, assuming your '77 is the same in this respect). This oil might tend to pool on the left side when the bike is idling on the kickstand, and somehow over time it plugs up the air jets - not the fuel jets - on the left carb ONLY. This has happened twice now, and I'm in the process of rerouting the breather hose to have its own air filter.

This would explain the fouling of the left plug (running rich), and the intermittent firing that you and I have both experienced.

It's just a hypothesis right now, so we'll see!

Mine has been doing the same thing. I like your idea, but my bike sits on a HD center stand and it is still just the left cylinder. Hmmmm?

 

[minnesota mike]

If you're not using the sidestand, then the left cylinder thing doesn't make any sense... if only someone had it happening on the right cylinder instead, we might be able to attribute it to a balancing issue. Is there anything inherently different about the two cylinders, other than their position on the bike? I don't know of anything

 

[Jonb]

Hey everyone, I just wanted to reply to all the folks that posted all of the helpful responses as well as the folks that kept asking questions cause without this great forum I would not have been able to figure out my bikes problem. I have a 83 heritage special with stock carbs,ignition and charging system ( I have a post called rebirth of an alternator). While my charging system and ignition are working like a champ, last week the bike started running on 1 cylinder. After replacing the coil adjusting the cam chain,adjusting the valves,checking wires for bad connections and making sure the battery was good (all these things and more suggested here) I went for the carbs. After a quick tear down and cleaning I reinstalled them I rolled her over and it took about 30 seconds and a little smoke out of the dead side she purred like new,then came the real test! I gave some throttle, instant power! After fine tuning the a/f mix its breathing really good. Tomorrow I'll sync the carbs and I should be back in buianess. Anyway thanks to all the folks that post,keep it up we need you. Good luck everyone