1981 GS650L misfiring all 4 cylinders

[aaron]

Hello All:

I'm hoping one or some of you can help me. I have a 1981 GS650GLX which hasn't been running quite right for the past year, and seems to be getting a little worse. It's a rough runner, especially during the warmup period. She likes to smoke a lot and often smells of raw fuel, and loves to backfire during downshifts. The kicker is, when I put a timing light on EACH of the spark plug wires, it showed an erratic misfire. Steady rapid blinks, then a period of misses; blink-blink-blink-miss-blink, etc.

After reading posts on here, I suspected a faulty igniter. However, I have gone through two of those with no change in characteristics (one was off of an '81 GS1000G, the other off an '82 GS650L). Also, I replaced the regulator/rectifier (also from an '82 GS650L), but put the original back on as it made no difference.

I checked the ignition coils per the tests in the manual and they passed. I understand this doesn't mean they're perfect, but that, combined with the fact that both would have to be faulty to cause the misfire to all 4 cylinders, tends to make me believe they're not at fault.

The other thing in question (in my mind) would be the signal generator, which I also tested according to the manual and was within specs. I have NOT replaced this part.

I hope I explained things okay here. It's probably good to note that the parts I used for replacements were eBay purchases. Any help would be appreciated. I miss the bike it used to be!!

Regards,
Aaron

[mark]

YOu could also have the same problems if the bike is flooding, if you're choke isn't completely closed for example. The "slowly getting worse" condition also indicates to me a carb problem more than electrics. Have you done any work on them, cleaned them, synched them for example? I doubt it, but it could even be something like your air cleaner is getting really dirty and is plugged.

Also it would help if you could take the bike for a ride and pull the plugs and let the folks here know what color they are. Should be a tannish color.

Is the bike stock? Stock exhaust, airbox or have there been any modifications? If the airbox is stock the seals need to be airtight or it won't run well. Also, check to make sure than on "run" your petcock doesn't allow any gas to flow when the bike is off.

[aaron]

YOu could also have the same problems if the bike is flooding, if you're choke isn't completely closed for example. The "slowly getting worse" condition also indicates to me a carb problem more than electrics.

I was stuck on the idea that it was electrics because of the timing light test. Would it stand to reason that this "misfiring" is because of flooding conditions?

Have you done any work on them, cleaned them, synched them for example?

No, I haven't. They probably do need to be cleaned/synched. Do you really think my problem is as simple as this? That would be amazing, and embarrassing.

Also it would help if you could take the bike for a ride and pull the plugs and let the folks here know what color they are. Should be a tannish color.

Will do...as soon as the weather cooperates.

Is the bike stock? Stock exhaust, airbox or have there been any modifications? If the airbox is stock the seals need to be airtight or it won't run well. Also, check to make sure than on "run" your petcock doesn't allow any gas to flow when the bike is off.

Bike is completely stock. Stock intake, stock exhaust, stock electrical system. Air cleaner is new, plugs are new. I checked the seals, both visually and using propane; it appears they are okay.

[mark]

I'm just speaking from my own experience. All my rough running, back firing, smoking at start-up has been carb or airbox related, so I was just wondering if you've looked at that at all. My timing light always does what yours does as well and nothing is wrong with my electrical system.

I suppose it could be electrical, you're problem. Have you read the stator papers on the Home page of this forum? Click on "what to watch for" there is tons of info on how to systematically check your electrical system. Get a good voltmeter and have at it. You need a fully charged battery as well for your ignition system to run good.

But the same symptoms could very easily be carb related as well. Stuck floats, plugged passages. Even a petcock assembly that was malfunctioning could cause the symptoms you describe. The vacuum line if its drawing fuel would mess you up.

It could be electrical. I'm just trying to give you other ideas and another way to look at the problem. I've had all those symptoms, misfiring, plugs not firing, blowing gas out the tailpipe, back firing etc......and it was all carb related.

[Hubbell]

timing light

Mark is right, unless you spent over $150.00 on your timing light, you can bet it will not be sensitive enough to pickup everything. Better way to test spark is to use the spark tester made for that which goes between the plug and plug wire and test one at a time. I never use a timing light to verify spark, it is just not proof.