Running on one cylinder

[nickklugs]

So I bet this has been answered many times but I can seem to find the right answer. Any-hoo it's only running on one cylinder, it runs very well on that one cylinder, and starts in 3-4 kicks without choke..... anyway the non-running cylinder sometimes runs for a few seconds, then stops and backfire's like a gunshot. Is it directly carb related or could it be spark?

 

[nickklugs]

Also could it be timing or do I need to adjust the valves?

 

[BBS360]

COULD be all of the above.
On these bikes it's likely the carbs.

Spark is easiest to check. Remove the plug, reattach the cable to the removed plug, firmly ground the plug body on the motor (use your boot to avoid possible 10+kV shocks), and hit the start button. If you see sparks you have sparks.

The rest you should be checking on a new bike anyways so check and adjust them all.
Set the points gaps BEFORE trying to adjust the timing. Anything else is an exercise in futility.

Seems like most people clean their carbs at least three times. The first time you'll think you were thorough, the second time you'll do a better job, and the third time you'll be desperate enough to actually take them apart all the way and do a proper job of it.
At least that's how mine went.

Some people pay to have carbs done but from the stories it seems like the shops only do an inadequate level 2 cleaning.

I don't recall from the other threads if you've done a compression test. It won't pin down any particular problem but does give a good indication of general cylinder health.
There's a procedure described somewhere on the forum for doing both a normal "dry" compression test and a "wet" test.
Do them both if you have access to a decent compression tester.
It's unlikely that one cylinder would have poor enough compression to misfire while the other would be ok, but it's possible.

 

[nickklugs]

Well I don't have a compression checker but when I remove the plug from the running cylinder and kick it over it seams to have the same amount of compression as the running one when I remove the non-running cylinders plug...etc, It's an xs360 with kick only, but when I remove the plugs it seams to have sufficient spark, But I am wondering if it is firing everytime..... which of course leads to the points gap. Does that make any sense? Or is if it has spark then the gap is fine...? Also would timing actually effect it that much?

Thanks,
Nick

 

[BBS360]

Could be any one of the above. One side's setting for timing, valve clearance, or points gaps could easily prevent a cylinder from firing.

From your description I'm leaning towards maybe that cylinder running too rich. Could be the idle mixture or...
I always forget to mention carb synch when these threads come up. When you have the carbs out for cleaning do a bench synch. Trying to do any kind of carb adjustments without first getting them synchronized is wasted effort. Once the bike is running decently on both cylinders do a synch with a manometer to really get it spot-on.

But you're still at the point where checking and setting everything is a very good idea.

Edit: Are the vacuum barbs on the carb boots capped and/or fed to the petcock? Stock setup would have one capped and one fed to the petcock.
Doesn't matter which is which but if one is open the air/fuel ratio will be off for that cylinder.

 

[lemonhead]

If you have air, good spark and compression, you probably have a fuel issue.

I cleaned my carbs once (quick & dirty) when I first picked up my bike. It ran okay...terrible throttle response & only ran on one side. Read about other people's issues with cleaning carbs, so I went all out and tore them completely apart, ran fine wire through jets to get the big crusties and then boiled everything in cider vinegar for a like-new clean. Also found out I had pinholes in the floats which was part of the problem. Ordered new floats, slapped it all together and poof...works like a champ.

Obviously, check plug gap, or buy fresh plugs to be sure they aren't the problem. With the plugs out and grounded, when kicking it over you should get a strong blue spark. (you should get a good rapid "snap, snap, snap, snap, snap" on a kick). Invest in a compression tester.

like this one

Twist the throttle wide open and get a reading, should be north of 155 psi (if I recall correctly) and both cylinders should be within about 5 psi of each other. (refer to the repair manual to verify) You can do the wet test too, which involves putting a small bit of oil in the cylinder (some use 2 stroke) to see if compression readings improve.

At this point, you'll be looking at cleaning the carbs. If that doesn't fix the issue, you could have some more in-depth issue, like timing, bad coil, poorly seating valves, etc.

A general rule to keep in mind when fixing things is to try the cheapest and easiest potential solution first and work your way up. Also, read your service manual cover to cover. It's chock full of good information and even has troubleshooting sections.

 

[nickklugs]

Okay I'll clean my carbs again and see if I missed anything .

Thanks,
Nick

 

[Palle]

Check your spark caps as well. Mine were a bit loose and ran on one til i hit higher revs. Glitchy so to say. just in case the clean dont help. (usualy is carbs thou)

 

[nickklugs]

Yeah it turned out that the pilot jet was clogged and the spark plug hole was stripped so it was loosing a lot of compression around the the plug threads. So I got a helicoil thread repair kit and fully cleaned the carbs. Started on the first kick.