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Discussion Starter · #1 ·
I ran into a bit of an odd problem this weekend. My #1 cylinder isn't firing. It's just shooting the unburned fuel out the exhaust. I switched plugs with another cylinder and it still did it. The coil runs another cylinder that's also working just fine. I'm baffled by this one. It's a Yamaha XJ650.
 

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It could be the plug cap or wire to the plug also. It could also be low compression.
 

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Discussion Starter · #3 ·
I was able to switch the caps around and that didn't fix it. Not sure how to go about replacing the wire since I'm not familiar with coil setups on bikes.
 

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Ok a couple questions.
Does it have points and condensors? If they are bad it won't fire on one cylinder.

Have access to another coil without buying one?

Does that cylinder have compression? If so how many PSI? It should be over around 120 PSI. That's just a guess on that one without havin' a manual.

You can check spark to that cylinder by putting a small screwdriver in the end of the plug cap and holding the metal part about 1/8" away from the cylinder head. Hold on to the plastic handle of the screwdriver so not to get zapped while someone pushes the start button.

Some bike coils you can replace the wire and some ya can't. I doubt yours are replacable without looking at it.
 

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Discussion Starter · #5 ·
I haven't seen anything about points and condensors in the manual so I guess it doesn't have those. I did the screwdriver test and I didn't even get a spark on a cylinder that's working. :confused: I guess the next step is tracking down a compression guage. Here are some pics of the coil I found on ebay. I even cleaned up that little connector with some sandpaper because it was pretty corroded but that didn't do anything for my problem. I wish I had another coil lying around to test.


There are 2 coils on the bike and each one runs 2 cylinders. Would it hurt anything if I switched the coils around?
 

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You should be able to switch them. If you don't have no spark you can assume it ain't a compression issue. A bike shop can test a coil for you with an ohm meter. if ya have an ohm meter and the specs you can check it.
 

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Discussion Starter · #7 ·
I tested the compression and all 4 showed the same. I also used this little tool that lights up if you're getting power to the plug. It showed everything is working fine. I've switched the plug on #1 to other cylinders and it works but none of the other plugs work in #1. Could the cylinder maybe be getting too much fuel? Maybe there's a short somewhere too. :confused:
 

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Is the plug all wet with gas when you take it out of number 1? If it is then I would say you are getting too much fuel. My CB fouled the #1 plug because of that last time I had it running.

Another thing it could be is it's getting spark when there is no load on the plug but when there is load, like compression, it won't quite fire enough or at all.
 

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If it was running and hittin' on all cylinders yeah. If not just look for a plug wet with gas. If it's soaked with fuel then you are gettin' too much. Sorry I can't help much more. You can hit it with some starting fluid in that carb and see if it fires over. Don't go crazy with the stuff, it ain't the best thing for gas motors but sometimes you have to do that to get one to fire over. Just spray a little to see if that cylinder kicks on or not. I hate using the stuff myself. Wish ya lived closer, it be easier if I could actually take a look at what's going on myself even with your good descriptions. Sometimes you just can't beat plain being there.
 

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Discussion Starter · #11 ·
I think I've got the mixture sorted out now. None of the plugs are dripping with gas anymore. But now my headlight won't come on when I go to start it. The bike just cranks and none of the cylinders seem like they want to fire. I'm about to hit the bike over and over again with the biggest sledge hammer I can find. :mad:
 

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Been there bud. Just go through the basics again. If it has a kick starter try kicking it over with a full charged battery. Sometimes ones that won't light of with the e-start will kick over. My KZ was like that.
 

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Discussion Starter · #13 ·
A rather ironic quote in my repair manual about the absence of a kick starter:

The system used is well proven and reliable
I took apart some of the connectors and cleaned them up since they were pretty badly corroded but no luck getting it started. I guess I'm spending an afternoon with the voltage tester.
 

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Discussion Starter · #14 ·
Well it turned out to be clogged carb that keeping the cylinder from firing. Now all I have to do is lean the mixture out some more to cut down on the black soon on the plugs and then (fingers crossed) she'll be ready to ride.
 

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Don't want to sound like a broken record Kajun but put a fuel filter in the line. A clear one you can see inside and can take apart to clean. If you,ve got some rust or other stuff in the tank it'll keep happening otherwise. Cleaning out carbs is a real chore.
 

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Discussion Starter · #16 ·
Yeah I was thinking the same thing earlier. Cleaning them sucks and it's even worse when you have 4 to go through.
 

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I ran into a bit of an odd problem this weekend. My #1 cylinder isn't firing. It's just shooting the unburned fuel out the exhaust. I switched plugs with another cylinder and it still did it. The coil runs another cylinder that's also working just fine. I'm baffled by this one. It's a Yamaha XJ650.
If anyone is still looking for a possible solution to 1 or 2 cylinders not firing one possible solution is a Vaccum leak. I confirmed this as I had the same issue. I removed the airbox, placed my hand over each opening of each carb, and the one not running was able to suck in fuel and fired right up. I also sprayed some carb cleaner on each boot and wahlah, fired right up. I will be purchasing 4 new boots and will post results. In conclusion, check for a Vaccum leak. All I see is replace the coils, clean the carbs for the 8th time, replace spark plugs, compression, plugs blah blah blah etc. Etc. Could be an easy fix with new boots.
 
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