Left cylinder issue

Alright almighty hive mind, I need help.

Got new tires mounted on the bike (1980 XS650G with Uni filters) and did and oil change (Valvoline 4 stroke 20w50) Saturday morning. I took it out a few different times on Saturday and rode her around most of the day on Sunday. She was running great! The top end seemed alittle noisier than usual but not too bad.

Well, I was about a half mile from home Sunday evening when I noticed the bike started running kind of rough. When I would slow down or let off the gas it was spitting and sputtering acting like it wanted to die. I had to turn the idle up a bit just to keep it going at stop lights. Even at an idle of 2k it was still spitting and sputtering and back firing, but only from the left cylinder.

I managed to get it home, I turned it off and let it chill out for a few minutes. Started it back up after about 10-15 mins and it did the same thing.

To me it seems like a carburator issue. I think this because I did some reading on here and saw someone say that if it backfires through the carb then it's running lean and if it backfires through the pipe then it's too rich. Is that correct?

I did check both plugs and they seem to indicate that I am indeed running a bit rich but the right cylinder is having zero issues.

What are some other things to check out?

It was running great, then on its own started running bad, so think about things that can quickly go wrong by themselves. Leaking float needle or o-ring. If your floats are brass, leaking float. Hanging float. Air leak at carb boots. Check valve clearance and compression to see if you burned a valve. If battery voltage is low, look at charging system.

My first check would be charging output, maybe it's stopped. That would cause the bike to run rough at lower RPMs once the battery was depleted some.

Your single dual output coil fires both plugs at the same time. If one fires the other should too. The only thing that would cause bad running on one cylinder only would be an issue with that cylinder's plug cap or it's connection to the plug wire.

Then yes, it could be a carb issue too. Maybe dirt got in and plugged some stuff up in the one carb. But check these other items first, they're simple and should be eliminated before you start tearing into the carbs.

Thanks for the tips XJ and 5twins!
After work last night I adjusted the Cam Chain and Valves. It is running MUCH better!

Before I adjusted the valves the right cylinder was at .005 and .007 and the left cylinder was at .005 and .010. They are now at .003 and .006 and running smooth and quiet!

It sounds like you might have an intermittent problem that could show up again.

Do you have a volt meter you can see while riding?

xjwmx said:

It sounds like you might have an intermittent problem that could show up again.

Click to expand...

Probably. This bike has been very finicky. I just need it to get.me through the rest of the summer and then I'll be going through it and upgrading/fixing things that it needs.

gggGary said:

Do you have a volt meter you can see while riding?

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I do not. That Is a very good idea though! Do you have an example? I am intrigued.

I forgot to mention that when I took off the rotor/stator cover, I noticed that the little wire that is soldered on to where the left brush is installed was barely hanging on. So I re-soldered that guy on.

the digital ones are couple bux a throw

This bike is now showing 8500 miles LED going strong, actually helped me figure out a charging issue a couple weeks ago.
but if your in a hurry the local big box has "cigarette lighter" versions with USB for less than $10.

gggGary said:

the digital ones are couple bux a throw
View attachment 147032
This bike is now showing 8500 miles LED going strong, actually helped me figure out a charging issue a couple weeks ago.
but if your in a hurry the local big box has "cigarette lighter" versions with USB for less than $10.

Click to expand...

Thats cool!! I'll definitely keep that in mind! How do you go about wiring one of those? Not too hard I would imagine.

Nope, a ground and a switched power wire. You want a switched power wire so the thing isn't on all the time, only when the key is. I have them installed on both my 650s now. The '78 Standard worked out pretty slick. I was able to fit it into the little pod between the speedo and tach .....



That wouldn't work on the '83. I had to build a separate mount for it .....

I am running this single LED multi colour read out for battery monitoring and been awesome for the past three years. I do clip on a digital read out gauge everynow and then for a full voltage check. Green is Good. Orange is not so Good. Red is Bad!
Nice small footprint and mounted off my gauge cluster bolt,
https://gammatronixltd.com/epages/b...6-4572-89a1-e89006e78fbe/Categories/Category1

This just popped up, I ordered two.

https://www.banggood.com/12-150V-LE...tqyEqsFrXezjPW5sR_Q&ID=47543&cur_warehouse=CN