1982 XS400 - right cylinder dies after a few seconds

[crib20]

Problem started a couple months ago, I was riding and the bike stalled out. I waited a few seconds, started it again, and it ran for a few kms before stalling again. Eventually it would only run for about 100 metres before stalling. Now, when it starts it sounds good (on full choke), but after a short time the RPM drops and the right cylinder does not seem to be firing (taking the spark plug wire off has no effect). I removed and cleaned the carbs and everything was spotless in there. However, I didn't know what to clean that controls fuel flow from one side of the carb to the other. Not sure if that is part of the issue.

Any suggestion??

 

[tstidham]

It could be the right coil going bad when it heats up. When it happens, check for actual spark coming out of that side. Depending on the year, it could also be the points for that cylinder or an issue with the TCI box as well.

 

[crib20]

It could be the right coil going bad when it heats up. When it happens, check for actual spark coming out of that side. Depending on the year, it could also be the points for that cylinder or an issue with the TCI box as well.

What I find strange is that when I prime the bike the right cylinder seems to run until it runs out of "priming fuel", so it seems like a fuel issue. However, to check what you mentioned above how would I test the spark right after the right cylinder dies?

 

[tstidham]

Harbor freight sells a cheap spark tester you can plug between the plug and pug wire and visually see the spark. Or do the screwdriver trick holding it close to the cylinder and look for spark.

 

[LeBouc]

What I find strange is that when I prime the bike the right cylinder seems to run until it runs out of "priming fuel", so it seems like a fuel issue. However, to check what you mentioned above how would I test the spark right after the right cylinder dies?

Is it possible that the tube between the 2 carbs would be partially blocked? That way, the bowl would be emptied while you run and slowly refill when you stop!

 

[crib20]

Update: I tested the coil and the spark continues after the right cylinder drops off (i.e., I don't think it is a spark issue). I tried running the bike while leaving it in "prime" mode, and the right cylinder does not drop out. Couple questions:

1) Is it safe to run the bike all the time in 'prime' mode (as long as I put it back to 'run' when I am done driving)?
2) Does the fact that the bike runs in 'prime' mode tell me anything about what might be wrong? Vacuum issue? Clog in the carburetor? Etc.

Thanks for all the help!!
Rob

 

[LeBouc]

Update: I tested the coil and the spark continues after the right cylinder drops off (i.e., I don't think it is a spark issue). I tried running the bike while leaving it in "prime" mode, and the right cylinder does not drop out. Couple questions:

1) Is it safe to run the bike all the time in 'prime' mode (as long as I put it back to 'run' when I am done driving)?
2) Does the fact that the bike runs in 'prime' mode tell me anything about what might be wrong? Vacuum issue? Clog in the carburetor? Etc.

Thanks for all the help!!
Rob

Hi Rob. Yes, it is safe to run the bike on prime; just don't forget to close it after riding otherwise, the pressure can force the fuel in the carbs and fload them. The problem you have is simple: the petcock filter is cloged and does not let enough fuel to the carbs and since the left carb is served first until filled, the left cylinder can continue working while the right one straves! Empty your tank, unscrew the petcock and clean (or change if necessary) the filter.

 

[crib20]

Hi Rob. Yes, it is safe to run the bike on prime; just don't forget to close it after riding otherwise, the pressure can force the fuel in the carbs and fload them. The problem you have is simple: the petcock filter is cloged and does not let enough fuel to the carbs and since the left carb is served first until filled, the left cylinder can continue working while the right one straves! Empty your tank, unscrew the petcock and clean (or change if necessary) the filter.

Thanks LeBouc ... I really hope this is the solution to the problem. I have been fighting this for awhile and it will be great to finally get the bike fixed.

 

[size030]

ok cool

 

[LeBouc]

Thanks LeBouc ... I really hope this is the solution to the problem. I have been fighting this for awhile and it will be great to finally get the bike fixed.

Please, tell us if that was the issue so that the next person going through the same problem can find its answer here!