Possible Bad Coil?

[jlyon40]

My GS850G is having trouble in the low RPM's and I believe it may be a coil issue. Here's the story. Before winter my brother(Mechanic) went through the carbs and cleaned them out(They didn't need much cleaning). Then we put them back on and all was good when I rode the bike. After it sat for the past 5 months of winter, I started her up and she started up normal. Checked fluids and everything before of course. Went to go for a ride after she warmed up since it was 52 out yesterday, and when the bike was under power in the low RPM's it was having a real hard time and almost stalling. When I have it in neutral I can rev the bike with no issues, but when I have the bike in any gear at lower RPM's it's bogging significantly until it pushes past 3500 RPM. I have already checked for air leaks and the carbs were working flawlessly before winter so I ruled those out.

I also cleaned and re-oiled my air filter. When I had the bike revving high before I took off in gear it pushed through better but it still had hesitation. Also when I was going in 5th gear and would let off the gas for a second and then go back on again the bike would hesitate. Lastly when the bike first started there was a couple of backfires but those stopped once the bike warmed up.

Possible solution:
I haven't checked the spark plugs yet and it's been about 10,000 miles since those have been replaced. So I'm going to get new ones and see if that might be my issue.
If that doesn't work I'm thinking that there's something wrong with one or both of the ignition coils.

If anyone has any ideas as to what it might be please let me know. Thanks in advance! My bike wouldn't even be running if it weren't for this forum.

[fastbysuzuki]

When you laid the bike up did you drain the carbs? Or if you did not drain the carbs did you use a fuel stabiliser?
Five months of the modern stuff they call petrol sat in a carb means bad news it turns into a jelly like substance if nor treated.
It sounds fuel fuel related to me a complete carb strip and clean is in order.
you could make sure the mechanical advance/retard mechanism is free and working if it's a pre 1983 bike.

[jlyon40]

Yes I let the carbs run dry before storing for the winter.

[jlyon40]

The gas in the tank is the gas from before winter. I topped it off before I stored it. Do you think I need to flush the gas and get fresh gas in there?

[LAB3]

Bogging under load sounds like an ignition issue to me and 10k miles on a set of plugs is well past the suggested service interval. Swap out the plugs and check the resistance in your caps as well.

[tom203]

Sounds carb related to me....gummed up low speed circuits. I prefer to run stabilizer thru carbs in fall and leave bowls full- over winter fuel will partially evaporate, but I've yet to have problems come spring (if it shows up).
drain bowls, add a good dose of carb ckeaner/ gas mix to them and let it sit for a day. You might get lucky!

[jlyon40]

Thanks for the input guys. I'm going to try running some carb cleaner through the bowls like you said Tom and I'm going to get new sparkplugs.

Hopefully that'll work

[jlyon40]

UPDATE:

I tried new spark plugs and using a good amount of gumout carb cleaner. I let the bike run for about 15 minutes to let the carb cleaner run through. No luck and now when I'm in idle it has a rough time revving in the low RPM's. My next idea is the go through the carbs again to see if they some how got gummed up. If they are all good then I'm not sure what to do. I've never checked the mechanical advance before. I don't even know where to start there, and if that's good too then my next thing to look at would be the coils.

The weird thing is that my dad's bike (80' 850G) did the same thing and we still haven't figured out what's wrong with his. So now we have two of the same bikes doing the same thing. Seems odd to me. Also when I let the choke off before the bike we idle fine but now it's slowly stalling out. Frustrating when you're not sure exactly what the problem is.

[bwringer]

...Also when I let the choke off before the bike we idle fine but now it's slowly stalling out. Frustrating when you're not sure exactly what the problem is.

Unable to run without choke is a pretty darn textbook indicator that the idle passages are clogged; these are the smallest holes in the carbs, and always the first to clog.

In your case, the clog may not affect all four carbs.

The carb cleanup series is your friend...

[jlyon40]

Thanks bwringer. I'm going to do a full clean and make sure nothing was missed before. Probably going to dip them too just to be safe.

[Gorminrider]

check your plugs.

The idle circuit IS important and exactly as above, pretty commonly dirty . But, if the choke-enricher is not a perfect "fix"- you still hear stuttering- might be you are getting too much gas-the bike will also run poorly at idle....a petcock failure at the vacuum line can make THAT particular cylinder stutter and occassionally pop in the exhaust... the plug might be gassy and blacker. OR if your float needles in a carb are not holding well...the bike can run well at high rpm but again, cannot quite burn all the gas it's getting at one or two cylinders....

[jlyon40]

Thanks Gorminrider! I actually have a leaking petcock right now and a new one is on the way so before I jump into the carbs I'll make sure to test with the new petcock.

Also thanks for the information. I noticed when I replaced the plugs that Cyclinder 1 was a lot darker than the other 3 so maybe it could be the float needles. I'll check all of it out and update!

[cowboyup3371]

Thanks bwringer. I'm going to do a full clean and make sure nothing was missed before. Probably going to dip them too just to be safe.

If you are going to do a full clean than it can't be a probably going to dip them but instead do the full 24 hours for each Carb dip process. You'll actually save yourself time and heartache in the long run

[canuckxxx]

Are all 4 pipes getting hot or do any stay cold or cooler than the rest? If 1 and 4, or 2 and 3 stay cold then coil could be bad or no power to coil. If 1 pipe stays cold then suspect the plug cap for that cylinder. Measure the resistance between plug caps 1 and 4, the between 2 and 3. You should get about the same for each pair at 20k to 25k ohms. If a pair has no continuity then try removing the plug caps and measure resistance between plug wire to plug wire. Wire to wire resistance should be 5k or 10k lower than with plug caps. If you find a bad plug cap then buy new caps for all 4 plugs.

[jlyon40]

I have checked the temps of the exhaust pipes and they're all in the same range. There wasn't one that was noticeably colder or anything. I'm going to go through like you said and check out everything on the coils. If those are all good then I'm going to move on to the advance mechanism to make sure that's good and moving freely. Maybe it needs cleaned and lubed up. If the problem still consists then I'm going to go through the carbs again. I'm doing the carbs last because I had just gone through them before winter and I emptied them out before winter. Hoping I can get this figured out, I saw an older thread about a guy going through this exact same issue and I don't know if he ever figured it out or not. The thread was abandoned.