Running on one cylinder off & on

[David M]

I picked up my new to my 1975 XS650 yesterday. The guy I bought from wasn't home but his wife was and she said the guy ran it up & down the driveway the day before and she said it sounded like it was running on one cylinder at times.

The bike fired up easily and off I went on my 30 mile ride home. The power was ok but not what I recalled from riding one many years ago. A few miles before I got home, it was definitely running on just one cylinder and I really needed to ride to clutch to leave a stop light. But then, a couple of times, like someone threw a switch, it sounded great and ran way better - lots of power ( for a 650 ). And just as suddenly, it shut off again.

This make me think it's electrical.

Can anyone offer what is more likely to be an obvious plan for troubleshooting this issue before I dig past a common problem ?

 

[davmo]

First thing check the charging system.
I'll bet its not working properly and needs new brushes. These things need a fully
charged battery to fire properly. David

 

[TeeCat]

Also, check your fuel supply: run in-line filters, petcock screens, see that your carbs are clean. I have this issue intermittently and the consensus is that it's fuel delivery-related.

TC

 

[5twins]

Many seem to think they can buy one of these old bikes, put gas in it, and ride off into the sunset. It usually doesn't work that way. They need a thorough going through. Check ALL the wiring. Start at the tail light and work your way up to the headlight, checking all the wiring, connections, and plugs in between. You'll probably need to clean the carbs as well. Practically all of these bikes need that when you 1st get them.

 

[David M]

Many seem to think they can buy one of these old bikes, put gas in it, and ride off into the sunset. It usually doesn't work that way. They need a thorough going through. Check ALL the wiring. Start at the tail light and work your way up to the headlight, checking all the wiring, connections, and plugs in between. You'll probably need to clean the carbs as well. Practically all of these bikes need that when you 1st get them.

Fortunately, I wasn't expecting perfection when I bought it and had anticipated what you are saying. It will ultimately be a street tracker but I want to get all of the electrical, fuel, ignition and mechanical things sorted out first before the tear down starts. I just checked the list of things that the previous owner did ( and he's a pretty knowledgeable, honest & reliable guy) and he had gone through the carbs so I'll put that towards the bottom of my list and look for the things mentioned above. I'll start by just putting the charger on the battery until the rain goes away and giving it a run around the block. I'm going to order an electronic ignition later today as well which is part of my build plan.

 

[XSLeo]

The po may seem knowledgeable, but unless he has spent a large amount of time with 30 year old bikes, his knowledge may not be up to the task.
More often than not when a bike runs like you describe the carbs turn out to be the culprit. The idle circuits in the carbs can plug easily. If one side has plugged idle circuits it won't run on that side until you rev it up high enough where that carb gets into the mid to upper range then that side will start to run, thus the sudden increase in power.
I might try removing the idle mix screws, count the number of turns out first. Use a can of carb cleaner, put the straw in the hole the screw goes in, cover with a rag. spray the cleaner. This can knock a blockage back into the float bowl. Put the mix screw back in and set to what it was.
Test ride, if it runs on both cylinders at idle then the carbs need a bit of attention.
The electronic ignition is a good thing if you don't like adjusting points. I have a 75, it runs great with the Pamco ignition.
If you think the problem is in the ignition then a thorough inspection of the ignition system will confirm this. Clean and properly set points work good. A bad condenser can make the bike run poorly. All easy things to check.
Imho the 75 is the best of the bunch. Good luck with it.

 

[David M]

<snip>
More often than not when a bike runs like you describe the carbs turn out to be the culprit. The idle circuits in the carbs can plug easily. If one side has plugged idle circuits it won't run on that side until you rev it up high enough where that carb gets into the mid to upper range then that side will start to run, thus the sudden increase in power.

I don't suspect the idle circuits. When things temporarily cleared up, it had lots of power right from idle and through the gears. ( Sorry for my poor description of what was happening.)

This is all really good stuff to add to the knowledge base between my ears though. Thanks for that.

David

 

[PhatTony]

I don't think alternator brushes will cause a problem like this. On a points system it will fire the coil all the way down until 4 volts. Pamco Pete has done several test to confirm this. If your charging systems goes it will run until it uses all the battery then you are stuck.

Carbs, ignition, coil, wiring or ???

 

[xjwmx]

One time I started running on one cyl about 100 mi from home and I figured I just limp back home on backroads but it cleared up in a mile or two and never happened again. When my tank is near reserve it will run on one cyl sometimes. But they;re right that you need to go through every connection and tighten it the best you can and make sure the carb passages are spotless. Good enough to get out of the driveway seems to be good enough for most people selling a bike. Of owners who try to do good maintenance, few know how thoroughly it needs to be gone through. So there's a lot of catching up to do on it.

 

[TeeCat]

If one side has plugged idle circuits it won't run on that side until you rev it up high enough where that carb gets into the mid to upper range then that side will start to run, thus the sudden increase in power.
I might try removing the idle mix screws, count the number of turns out first. Use a can of carb cleaner, put the straw in the hole the screw goes in, cover with a rag. spray the cleaner. This can knock a blockage back into the float bowl. Put the mix screw back in and set to what it was.
Test ride, if it runs on both cylinders at idle then the carbs need a bit of attention.

This is worth printing out and taping to the fridge! I'm going to do this this weekend, then clean the pilots, as I have a similar intermittent issue.

Thanks, Leo!

TC

 

[ann0yed]

I had that problem and after taking the carbs off and cleaning them a thousand times and replacing a bunch of electrical stuff, I bought a multimeter and discovered it was a plug wire.

-j

 

[Beau]

When I joined the site I peeked through the info provided.

Check it out, it has already helped me out. Most of the stuff they recommend probably wouldn't hurt to do to a good running bike. It will at least give you a true life idea on what you need to do, and also make you more knowledgeable about the way the bike works.

http://www.xs650.com/forum/showthread.php?t=367