No spark on left side?

[dawson128]

Howdy guys, 91 here.

My bike has been doing this thing where it will run great for a few minutes after starting it up and then I will immediately lose spark on the left side. If I let the bike sit for a while and start it back up it's back to normal. I've ordered a replacement coil as that's what I suspect it may be but was just looking to see if anyone has any input? What else in the ignition system can fail due to heat? It's only on the one side..

Thanks for any help

[dawson128]

Gonna add something. I forgot that I think I tried switching coils but I can't remember if it was the left one that gave me problems before I switched them or not.. either way gonna replace the coil. Let's say that doesn't work.. you think it could be the signal generator? Is it possible for these to fail on one cylinder?

[qcbaker]

I think you're on the right track with the coils, followed by the signal generator. I would also check the plugs themselves. They're probably good, but it cant hurt to double check.

[dawson128]

How's it going guys! Update on this thread. I got a new coil in the mail and just installed it today. Went on a ride to fill up with gas and went right back home. 10 minutes or so of heat soak later I come outside to start the bike up and the left cylinder is down on spark again..

Before I pull the trigger and order this expensive signal generator, is there ANYTHING else that could fail that's heat related.. dealing with ignition obviously.

Thanks as always.

[W201028]

Did the new coil come with a new plug end? Ive had those fail in the past, and if you reused the old one it could be the issue

[dawson128]

Did the new coil come with a new plug end? Ive had those fail in the past, and if you reused the old one it could be the issue

Came with a new plug cable and plug end yes but can't see that failing with heat anyways

[W201028]

Those plugs get pretty hot, but if its new that is probably ruled out.

Do you have a multimeter? If so, you could touch one probe to the coil input, and ground one on the engine. Set to volts and run the motor cold, and then warm it up and check again. If the voltage supply to the coil is dropping it may well just be a bad wire.

The signal generator tells the igniter to send voltage to the coil, but it does not supply the voltage, thats the igniters job. So it could rule the generator out.

The manual says you need a special ignition test tool to check the signal generators, but maybe you could disconnect both and check the resistance of each generators. If the left one is way different that might indicate a problem. But I am speculating, its not what the manual says.

[dawson128]

Those plugs get pretty hot, but if its new that is probably ruled out.

Do you have a multimeter? If so, you could touch one probe to the coil input, and ground one on the engine. Set to volts and run the motor cold, and then warm it up and check again. If the voltage supply to the coil is dropping it may well just be a bad wire.

The signal generator tells the igniter to send voltage to the coil, but it does not supply the voltage, thats the igniters job. So it could rule the generator out.

The manual says you need a special ignition test tool to check the signal generators, but maybe you could disconnect both and check the resistance of each generators. If the left one is way different that might indicate a problem. But I am speculating, its not what the manual says.

I may have read before about the testing and I think I remember reading in another thread that it didn't work so well. But even if it did work I am the BIGGEST moron when it comes to electrical. Even if I had a multimeter I wouldn't have a clue how to read it.. The way I see it only 4 things can go bad. Plugs, Coils, Cdi, and signal generator. I've rules out plugs and coils, and I can't see how a Cdi would fail for only one side and it doesn't really have anything to heat soak off of so I would say it must be signal generator right?

[J_Walker]

the early model crank trigger are all over ebay. i'd check that first before dropping 150+ bucks on something "new"

[dawson128]

the early model crank trigger are all over ebay. i'd check that first before dropping 150+ bucks on something "new"

I'm looking now and can't find any except for one for an 81-83.. maybe I'm searching the wrong keywords or something.

[W201028]

Roll the dice on the signal generator then I guess. I am with you, the ignitor is mounted well away from any heat sources, although it doesnt rule it out. Electricity generates heat, and heat equals resistance. Just remember that between those four parts that could fail, there are feet of wire and plenty of connectors.

At the very least, take all the connectors apart and check them for corrosion. What you are looking for is any of the pins in the connectors having a greenish-blue color. If any are suspect, get a can of contact cleaner and spray them down until clean.

[dawson128]

Alright, my new signal generator came in and I need a bit of help. The new one looks nearly identical except for the harness on the end. Does anyone have a wiring diagram for the signal generator?

The black, green and white, and brown wire go into the harness that connects to the CDI and the green and yellow wire goes to a spade bit. It seems to just be a ground to me though as it's not connected to the coils on the signal generator.

On the new harness, all four wires go into one harness instead of having the green and yellow separate with the spade. I'm going to splice the old harness onto the new one just so it matches, but I'm curious how it's supposed to be?

Wiring diagram anyone?

[dawson128]

Update: found a wiring diagram that I can actually read  looks like the separate wire runs to the oil pressure switch. Makes sense why it's separate because I have aftermarket neutral light and I guess apparently oil pressure light on the handlebar. Will update once the new coil is in.

[Big Rich]

Just read this and was thinking - have you actually checked for a spark on the left side? Somet8mes people say the left side isn't running, but haven't physically checked for spark. If not, you should check the vacuum hose from the left carb. If it has a leak, the right cylinder will run, but not the left

[dawson128]

Just read this and was thinking - have you actually checked for a spark on the left side? Somet8mes people say the left side isn't running, but haven't physically checked for spark. If not, you should check the vacuum hose from the left carb. If it has a leak, the right cylinder will run, but not the left

I have not physically checked for spark aside from pulling the wire off the spark plug and having it not shock the sh** out of me lol. However I can't see a vacuum being intermittent/heat related, when I lose spark, it is instant. There's no in-between. I have to let the bike cool down and my spark will come back.

[dawson128]

Well.. I pulled the trigger on the signal generator and...  I THINK IT WORKED! At least for now! I have been riding it around today, shutting it off, riding it more, and shutting it off again and it has still no issues.. but even if it does come back, the only other thing to replace is the CDI