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Discussion Starter #1
First time posting here, absolutely stumped. My bike is a 1990 Ex500. It's been only running on 1 cylinder. When both coils are connected only the right cylinder fires. but when the right side coil is disconnected from the spark plug and only the left is connected the left fires. And again when both are connected only the right side fires. Any ideas? I'm pretty dang stumped, thanks.
 

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strange one that. of course one assumes the battery is serviceable. the bike is charging at a proper rate all connectors are clean and tight and the flywheel hasn't lost any magnets. all that being said. it does seem to be a power issue as if there is only enough power to fire one plug at a time have you tried shutting the gaps down to 12 thou. and/or swapping plugs over to see if it changes cylinders.
it seems also the right side is dominant try swapping the whole coils over to see if it becomes left side dominant.
then if all else fails the inevitable conclusion and next step is the CDI. while these are a solid reliable unit it is possible for one to go faulty. but I would try everything else first. then get hold of a second unit to try (it can be kept as a spare if not used).
 

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strange one that. of course one assumes the battery is serviceable. the bike is charging at a proper rate all connectors are clean and tight and the flywheel hasn't lost any magnets. all that being said. it does seem to be a power issue as if there is only enough power to fire one plug at a time have you tried shutting the gaps down to 12 thou. and/or swapping plugs over to see if it changes cylinders.
it seems also the right side is dominant try swapping the whole coils over to see if it becomes left side dominant.
then if all else fails the inevitable conclusion and next step is the CDI. while these are a solid reliable unit it is possible for one to go faulty. but I would try everything else first. then get hold of a second unit to try (it can be kept as a spare if not used).
I just swapped the plugs and still the same results. The battery is good, I just bought it yesterday. One thing that I did find out is when the right side is disconnected and its just the left side running it runs very poorly, like it requires choke to run and constant throttle. in comparison when it is the right side running it idles fine without assistance. Do you think it could be a lack of fuel issue?
 

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When you say "Fires" do you mean it sparks with the plug out or testing the wire. Or is the cylinder actually running?
Sounds like a simple Clean the insides of the plug caps and check (renew) all the high voltage connections.

FOG
 

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there could be a secondary issue with the carbs. but that was not the question one plug fires one doesn't isn't the carbs.
 

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Discussion Starter #6
When you say "Fires" do you mean it sparks with the plug out or testing the wire. Or is the cylinder actually running?
Sounds like a simple Clean the insides of the plug caps and check (renew) all the high voltage connections.

FOG
When I say fires I mean that the cylinder is running. Both plugs seem to spark but only one cylinder runs at a time.
 

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Misleading use of the word "fire". Spark plugs "fire".....EX engines run on either none, 1 or 2 cylinders. Your latest post indicates possible carb fuel circuit and/or synch issues.

Confirming spark is indeed present on both cylinders a starting point to totally eliminate an ignition issue. Fogs suggestion valid. Then zero in on carb diagnosis.

Some background? Bike been sitting dormant or been running prior? Did this happen all of a sudden or was it discovered in waking the bike up after a long dormancy? Bike new to you or you a long time owner?
 

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Misleading use of the word "fire". Spark plugs "fire".....EX engines run on either none, 1 or 2 cylinders. Your latest post indicates possible carb fuel circuit and/or synch issues.

Confirming spark is indeed present on both cylinders a starting point to totally eliminate an ignition issue. Fogs suggestion valid. Then zero in on carb diagnosis.

Some background? Bike been sitting dormant or been running prior? Did this happen all of a sudden or was it discovered in waking the bike up after a long dormancy? Bike new to you or you a long time owner?
I bought the bike as a project/ starter bike on craigslist about a week ago. the guy I bought it from said it ran well and all that. Well that's not the case. Anyway I don't know a ton of its history but I can say it hasn't been maintained very kindly. lots of "good enough" or getto fixes. When I first got it running right (came with a completely shot battery and a broken ground for the starter) I noticed it sounded horrible, so I assumed one cylinder wasn't running which turned out to be the case.
 

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wish I had a dollar for every time I have heard that one. if the seller can't or won't start it so you can see it running it's a non runner. and you do the runner in the opposite direction.
 

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wish I had a dollar for every time I have heard that one. if the seller can't or won't start it so you can see it running it's a non runner. and you do the runner in the opposite direction.
Starting to wish I walked away from it. Felt to committed though because I drove 2 hours to see it and he said "the battery just went flat"
 

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As FOG was talking about start there. Clean all the connects and verify all connection are properly connected. Then move on from there.

My bike, I bought it in Dec as a project and it was running and I knew it was not running correctly. One side was over 100 deg cooler on the exhaust straight out of the engine. I rebuilt the carbs now they are within 10-20 deg of each other. Start with the basics and easiest first work your way down. These bikes are simple and if you do too much at once and go to swapping things without a methodical means you might as well toss it in the corner and let the junk pile on it, or take it to a shop and pay out big $$$ and that be that rather than pay $$$ and get nothing but a bunch of extra parts laying around a non-runner...
 
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the battery is always the excuse as to why it won't start. we have all been there. best option when that occurs I'll go for a coffee while you get it started. if it starts I'll buy it if not see you.

if now stuck with it and you bought it as a project. just turn it into a project strip it re paint it all service the engine while it's out do all the jobs one by one take your time and enjoy the work.
 

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PO is your intention a restoration to full factory glory or a "get it running and street worthy" project?
 
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PO is your intention a restoration to full factory glory or a "get it running and street worthy" project?
The whole intention was getting it street worthy to start. Ive been riding bikes for a while and just wanted something of my own to ride. the seller said it needed plastics maintenance. But it seems I'm stuck with it. To move on I think I'm gonna take off the front fairings and getting a close look at the wires to see any obvious corrosion.
 

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Ok then. Nothing wrong with a strip/inspection. At that time, I'd strongly suggest throwing a valve clearance check on it. Especially in view of the fact that your PO was a slacker. Dunno why, but many EX owners blow off valve clearance checks. I've encountered locals here with near ZERO clearance on every exhaust valve.
Last year, a guy with every intake valve near zero....yup, would run just for a moment and then crap out (technical term). Once brought to spec, the standard EX top end clicking/clacking was evident, but ran fine thereafter. Some require accompanying carb work as well, every one finished with an accurate sych. Voila, each one fully road worthy.
 
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Most common bs you see on for sale posts. "Has been sitting for a while, ran when parked, just needs battery and fresh gas."

From the sounds of it you are probably best off just servicing the carbs, valve clearance adjustment, sync the carbs, and service the coil wires, and replace the plugs. If you are mechanically inclined then this will mostly just cost you time and effort, and a pair of carb gasket sets and spark plugs.
 

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Discussion Starter #17
53694

So when I took the front plastics off I saw this. appears to be a ground that hasn't had a very good time. Anyone know what this is a ground for?
 

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Good find.....irresponsible for PO to let that go.....thats an important main front frame ground point, branches out to lighting and other systems.

You have the Gen 1 elec schematic contained in a service manual?

That found, you'll likely now need to closely inspect harness for other defects/errors. Once engine starts/runs of course, any non functioning electrical items will become evident. Front ground supplies all instrumentation lighting, headlight, turn sigs, cooling fan, cooling sensor.....you really need to source a proper schem.

I'd venture to say, with that ground gone, certain lighting not gonna work.....now you know why the seller left the battery dead. Fully INTENTIONAL.
 
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Good find.....irresponsible for PO to let that go.....thats an important main front frame ground point, branches out to lighting and other systems.

You have the Gen 1 elec schematic contained in a service manual?
I don't, wasn't included in the purchase
 

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right that wire is the front aux earth wire. it has burned out due to overheating. seeing as earth wires cannot short out on their own (being earth wires). it has been over loaded. take the seat off and look for the main earth wire.
it is a thickish black and yellow wire that should be connected to the jumbo negative wire near the battery with a bullet connector make sure this is connected and clean.
then check the rest of the wiring for burned connectors (possibly on the RR) or ignition switch.
 
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