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Old 05-15-2011, 04:03 PM   #1
flyin'fatass
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Default Only firing on one cylinder

My grandfather and I are working on an old honda CB500T barn find. It's got a lot of work left before It'll be good enough to ride, but for the time being the motor is the main concern.

Right now the motor turns over and runs, but only on the left side cylinder. The right side isn't getting a spark. A spark tester as well as removing the plug and running it outside of the cylinder proved this. I thought it was either the ignition coil or the points. I checked the coils and it seemed the right side coil might have had a connection break somewhere in it. I replaced it with another set of ignition coils from a bike we had upstairs (might have been the cb450?), which i checked and all the connections were good, yet it still only ran on the left cylinder.

After this i decided to check the points. I had looked them over before and, with the origional coils, I noticed that the point for the right cylinder didn't spark at all. With the coils i pulled off the other bike installed, both points sparked, but still no firing on the right cylinder. The wires coming from the points didnt seem to have a breaks in them (ill check to be 100% sure later).

I made sure all of the connecters were good and plugged in, so that wasn't the problem.

The only things that I could think of would be either that the right side plug is bad (I'll check that later by switching the plugs), or that somewhere between the points and coils, the right side wire has a break somewhere in it.

Any ideas as to whats causing it to only run on one cylinder?
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Old 05-15-2011, 07:31 PM   #2
Gumby73
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Well, the fact that you've confirmed it's a spark issue narrows down the search.

I would say you're on the right track with the wiring. If it's not getting spark and the plug turns out to be good, it has to be a wiring issue- it's just matter of deducing it.
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Old 05-15-2011, 09:46 PM   #3
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Quote:
Originally Posted by Gumby73 View Post
Well, the fact that you've confirmed it's a spark issue narrows down the search.

I would say you're on the right track with the wiring. If it's not getting spark and the plug turns out to be good, it has to be a wiring issue- it's just matter of deducing it.
well the plugs are good, I just tested them. I also ran the connectivity tester between the points and the wires that go into the coils and theres no breaks.

I swapped the coils from the 450 onto it again and then it sparked on both sides. I ran a voltage tester and they were both making the same voltage (I didnt mind looking how many volts; since one side was firing, if the other got the same, then it should fire as well). Yet when i put the plugs in, it still only ran on the left cylinder. I pulled the plug again, and it sparked outside of the engine, but when I put it in, the right cylinder would never ignite.

I'm still baffled at whats causing this. The ignition system is pretty much isolated from the rest of the electricals on this bike, and I've gone through everything that could have been causing it to not fire. I'm almost certain compression is good (though I dont have any way to accuratly check it).
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Old 05-15-2011, 11:42 PM   #4
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On the spark plugs,just firing a plug outside is not a great way to test them. A better way is to take a plug and straighten out the electrode. The idea behind this is if a straightened plug will fire outside the engine,a properly gapped one will fire inside the engine,where the presence of pressure and gasoline actually make it harder to produce a spark. Another good way to see the relative spark strength is with the old school timing light.
It is also entirely possible that a previous owner completely screwed up the idle circuit adjustment [when the bike was not sparking] trying to get it to run.
You could remove the plug,put a few drops of gas in the piston,and see if the dead side then fires up. It would not be the first time that there was both fuel and spark problems on the same piston...
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Old 05-16-2011, 11:59 AM   #5
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If you are getting spark to both plugs with one setup slumlord has a point with a fuel issue. Does the bike have more than one carb? It may not be getting fuel to that cylinder.
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Old 05-16-2011, 12:03 PM   #6
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Don't know what year the bike is but I would assume that if it has points it also has condensers. I don't have any idea how it's set up but if it does have condensers try swapping them and see what happens.
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Old 06-26-2011, 05:36 PM   #7
mrheartman1
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Default Right cyl

I would pull the right plug & crank over the motor with my thumb on the plug hole . It should blow your thumb off the plug hole . Pretty simple test . Good luck .
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Old 07-03-2011, 10:47 AM   #8
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make sure the wires running to the spark plug are in good order
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Old 07-06-2011, 04:42 PM   #9
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Default one cyl cb500t

Remove the point cover and check to see if you have power to both sets of points.Also check to insure that the side that is not firing has the points installed correctly(point wire not shorting to ground) . With the key on and the points open you should have battery voltage at the points.if you do not check the coil on that side(note*you can remove and switch the coils)to rule out a bad coil.You should have battery voltage at the coil with the key on and the engine stop switch in the on posistion.
power comes from the battery to the ignition switch,from the ignition switch to the engine stop (kill) switch,from the engine stop switch to the coil.
It has to be one of mentioned things.
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