Engine stalls and misfiring: GS 850 GL (1980)

[Anonymous]

Hi everyone,

I'm new to the GS and working on them, so please bear with me.

I just got my 850 running and have put about 200 miles on it. It has been running well for the first 150 miles, but began running rougher in the last 50 miles. Last night I was riding home and the engine stalled at a stop light. I got it started after a coupel of tries. The engine was running rougher. It felt like one or more cylinders were not firing at times. I made it home, but each time I would accellerate it would buck like it was missing. When I ran at about 3500 RPM it seemed fine, until I woudl accelerate again. When I pulled into the driveway it stalled after sounding like it was missing at least one cylinder.

All manifolds felt hot. I also have a sock for an air filter (I know I just got a new Uni and will put it in tonight)

So I am looking for a place to start. Air? Intake? Fuel? Plugs? What's your best guess

[AOD]

sounds like ignition coils to me...i had the same happen to my 550 before i put on Dyna coils and ignition. i dropped 2 cylinders going to work one day, which made for a slow ride....

what my old 550 does is when the coils get hot, ie-sitting in traffic or at a stop light, it stops firing everytime it should. once you get moving it cools off and returns spark. some coils may not cool off enough to start sparking again.

a good check to this would start it up cold and see how it behaves. if you have a problem cold, check the plugs and wires for spark. if you dont have a problem, get it nice and hot and see if it acts up.

easy way to check for spark at a plug wire without removing the plug is using a timing light. you need to make sure the plug is sparking though as well.

~Adam

[Anonymous]

how can I be sure it's the coil

I started it this morning with no problems. Starts right up. I let it idle for 5 minutes and then went for a short ride. No problems. When I came back it was running rough. It did not stall though.

How can I be sure that the coil needs replacing? The dealer cost is $90 per coil. Are there any after market coils that will work just as well that may be less expensive?

One thing I forgot to mention was that the day before I ran into problems I got caught in a pouring rain. Me and my GS got soaked. After this I noticed that my tach was no longer working. I have not checked the cable yet, so I don't know if there are any breaks or not. This may just be coincidence. But I thought I'd throw it in.

Thanks for the tips. I hope to get working on this weekend.

[KEITH KRAUSE]

If your problem is electrical related, you should first do a basic inspection. A "new" bike should always be completely checked over anyways.
I would at least check all the connections in the harness related to spark. A connector that's getting hot will act as you describe. Check the connections where the coil leads go into the plug caps. Clean them up or snip off the end and make a new connection if the leads are long enough.
You may want to replace the plugs too and set the gaps. Verify correct plug type. Check the connections on the coils, etc. Fill the battery correctly with distilled water and clean/tighten its connections.
It may also be mixture related. If the problem gets worse as the bike heats up, this is generally a rich condition. At least replace that filter. The sock may be more restrictive than you think.
It could also be fuel flow related. The carbs may need cleaning. At least check/replace the vacuum line to the petcock and clean out the gas cap vent. Look inside the tank for signs of rust. Fine rust particles will also cause your described problem.

[AOD]

i agree with Keith in that you should go through the bike and make sure everything is in good shape. A basic tuneup is a good start. Charge the battery, change and regap the spark plugs, check the air filter.

If you want to get in some good work, you can start by removing the carbs and given them a cleaning. the process takes as little as a half hour once you learn how to do it. this website has a good carb cleanup series on the main page, if you need a walk through.

for other info, such as spark plug gaps and other maintenence issues a Clymer or Suzuki repair manual are a good investment.

~Adam

[Anonymous]

Thanks

Thanks Keith and Adam,

I plan on replacing the air filter, checking the plugs, cleaning/replacing the vacuum tube, checking the connections. I hope it's something as simple as a wire that is not connected well enough, or even the plug wires.

I have a Clymer manual. It looks like a great help. I changed the plugs a week ago, got a new battery, changed the R/R (I have a parts bike too), and cleaned the carbs. I guess another cleaning would not hurt. Takes me a bit longer than a half hour to clean the carbs though. The tank looks ok. But I will keep an eye on it. The original tank was pretty dented and rusted. I swapped the tank from my parts bike.

I have a bunch of stuff to do this weekend it seems. Thanks again for the suggestions

[KEITH KRAUSE]

Re: Thanks

Thanks Keith and Adam,

I plan on replacing the air filter, checking the plugs, cleaning/replacing the vacuum tube, checking the connections. I hope it's something as simple as a wire that is not connected well enough, or even the plug wires.

I have a Clymer manual. It looks like a great help. I changed the plugs a week ago, got a new battery, changed the R/R (I have a parts bike too), and cleaned the carbs. I guess another cleaning would not hurt. Takes me a bit longer than a half hour to clean the carbs though. The tank looks ok. But I will keep an eye on it. The original tank was pretty dented and rusted. I swapped the tank from my parts bike.

I have a bunch of stuff to do this weekend it seems. Thanks again for the suggestions

In this case, when you're not sure what could be causing the problem, it's always best to just do the easier checks first. General maintenance that needs doing anyway. If you re-test and still have a problem, you try a few more things before getting into more technical/costly stuff.
The electrical connectors are easy to check and you can generally see if a problem exists. If the brass connector looks pinkish or discolored, you have a connector burning up. If you have any green or white/gray on your copper leads you have corrosion, etc. Cleaning the gas cap vent is important and a blocked vent commonly shows itself when it's hotter. The vacuum line can have cracks that open up more with heat. The petcock may need a good flush. You may even have your mixture screws set a little too rich, if they've ever been moved. But don't consider playing with them until the maintenance stuff is covered.
There's a lot of things that can cause your problem. Try the easy stuff and go from there. Let us know how it goes.