Right cylinder not firing '82 GS300L

[Hamcake]

Hi there -
I have a 1982 GS300L that I bought a month ago, that's having some issues with the right cylinder. Hope someone can help.

A few weeks ago, it wasn't starting, so I pulled the plugs and set them against the cylinder head, and saw the right one wasn't sparking. I replaced it (both are D8EA), and it was sparking... though it still wouldn't start, but the next day it started up.

I put some seafoam in the tank, rode it for a day or two, then gassed up again. I haven't pulled apart the carbs, but I imagine they could use a cleaning. Sometimes it will leak gas from a tube sticking out the bottom of the bike, which is assume is an overflow from the carbs.

A few days later, it was running very poorly, with very low power. The right cylinder wasn't hot, so it must not be firing.

I measured resistance on the coils:

• Left coil primary: 5 Ohms
• Left coil secondary: 23,600 Ohms
• Right coil primary: 5 Ohms
• Right coil secondary 22,500 Ohms

Based on the "GS250T-GS300L '82 Service Manual" on BikeCliff's site, it says it should be:

• Primary: 3.5 – 4.5 Ohms
• Secondary: 23,000 – 25,000 Ohms

Are these measurements far enough off to cause this issue?

I measured voltage at the coils: Left: 10.08 V and Right: 10.10 V.
Battery has 12.35 V

I removed the right spark plug boot, and measured it at 9.46 kOhms — but I don't know what is normal. I cut off a centimetre from the wire, and reattached the boot.

In the meantime I put 100% seafoam into the carbs and let them sit overnight and then drained.

Started the bike, ran it, but again, the right cylinder still wasn't hot. Took the right sparkplug out, and it was wet, so it's getting fuel. Put the plug against the cylinder head, and it was sparking... not super bright blue though. But then at some point it stopped sparking.

Any thoughts on what I should do next? Bad boot? Did I reattach the boot wrong? I haven't checked the valves — something there?

Thanks!
Hamcake

[Suzuki Mad]

There are lots of 'could be's' trying to sort an issue down.

To make an engine run you need several things. Spark, fuel, air and compression. Have you got all of those?
So start with one thread till that part is sorted.

You have no or an intermittent spark on one cylinder. Chase that fault down first.

Points or CDI?

Is the plug wet in the cylinder that isn't firing?

Try the old plugs incase you have a duff new plug.

Go through the wiring circuit from the points/CDI to the plugs. Check each connector is clean and good.....

Then when you have a good spark move to the next issue.

Valve clearance wont alter lack of spark.

[Hamcake]

Thanks - I'd been thinking a fuel issue could have been causing the plug to foul up, and stop sparking (plug was black) but things seem to point to an electrical issue as the primary thing.

At least the left side is sparking, so I think that narrows it down to the coil onward... I'll focus the and start moving back up the chain.

-Hamcake

[Suzuki Mad]

Once you have a strong spark then go after fouled up plugs, fueling issues, air box, pods, O rings seals, carb boots etc etc etc.

Be nice to also drop a 'Hello' in the GS Owners part on the forum too.

[Hamcake]

Oh I noticed you had done followup questions:
- no points. Signal generator and ignitor. Previous owner has to replace the ignitor, because it wasn't running well
- yes, plug was wet when I pulled it
- ok, I'll try a new plug, or switch the left into the right. Good idea

Thanks!
-Hamcake

[Hamcake]

I switched the left and right coils with each other, and it's still not sparking on the right side... so I switched the plugs with eachother, and the problem switched sides. Cleaned up the sparkplug, and I'm getting a nice spark from both sides.

In the process of doing this I also filed the connections on the coils and cleaned them with contact cleaner spray.

I ran it for a minute or so, and both cylinders get hot (yay!) but the right one is noticeably less hot than the left.

Also noticed some smoke coming from the cross-pipe on the exhaust, and some dark stuff dripping out.

Starting to think the non-sparking issue is just being caused by the plug getting fouled on the right side, and is a symptom of the root cause...

Some other leads I'm following up on, and getting some theories by searching this forum:

Gas is dripping from the hose at the bottom of the airbox:
- Pretty sure it's gas. Smells like it, and evaporates quickly
- Doesn't seem to be coming from the breather tube from the cylinder head, since it's dry in there. I'll doublecheck though.
- Maybe the float isn't working right?
- Maybe gas is coming in through the vacuum tube on the petcock?
- Oil is very dark, but there doesn't seem to be gas in it...? It would float on top, right?

Maybe valves need adjustment:
- This has been in the back of my head since I got the bike, since I know it's important.
- Bikes seems noisy, but I can't tell if it's from valves.
- Maybe this is causing the plug to foul up?

Well, at least it's been crappy riding weather

-Hamcake

[Hamcake]

So I checked the valves which was kind of an interesting task -- never done that before. There was zero clearance, as far as I could tell.

I set them to .005" which is the upper end of the spec. Started it up last night, and my gut told me it was running better - but it was late so I couldn't run it longer.

I also tested the petcock, which was working as expected: On and Res don't leak, and send fuel when I suck on the vacuum line. And I didn't have any fuel coming out of the vacuum

BUT: this morning, I went to start it, and it would not start I'll check again this evening to see if I have spark, and what the plugs look like.

Fuel, air, compression, spark. Should be easy, right?

-Hamcake

[fbody_mike]

Did you set the valves with the engine cold, as in not run for 8 hours cold?

[Hamcake]

Did you set the valves with the engine cold, as in not run for 8 hours cold?

Yes, pretty sure I hadn't even started it all day. I'm assuming things would be tighter if the engine was warm. Pretty sure I only started it after working on the valves.

Today, I put in fresh plugs because the current ones were pretty dark. NGK D8EA.

Right cylinder doesn't feel hot.

Pulled out the right plug, and it's wet. When I place it against the cylinder head, it's giving a bright spark.


-Hamcake

[Redman]

Ham, Doesnt sound like your problem at the moment, since you say the right is sparking, but that right cap measuring near 10K is way up from the normal 5K. And they do go high until almost completly open (infinite resistance). They can be replaced with NGK brand, are 4 or 5 bucks each.

.

[Hamcake]

Thanks Redman -
I've measured the left boot and it's at 10.45 kOhms. Funny that they're such high values. So unless anyone can think of a reason why these should be 10 kOhms - sounds like it'd be wise to replace them, especially since they're cheap.

I'm pulling out the carbs now, because it's only a matter of time before someone chimes in that I need to thoroughly clean the carbs and replace the o-rings

Lots of the posts on here where someone's got a dead cylinder, ends up being the pilot jet, from what I've seen.










They are pretty filthy, and the left one is overflowing and leaking. I'm cleaning up the exterior now, and my neighbour has an ultrasonic cleaner, so that should get things super clean.

-Hamcake

[Hamcake]

Oh, and I'm not sure why but the right carb has a mesh ring in front of the butterfly valve, but the left one doesn't...
-Hamcake

[Gorminrider]

yes those carbs are kind of odd. Same thing on the 250 and I only see one screen on the fiches (part 58)...there was one member here who had a 300. you might try a search and see if you can find a thread because he figured it out. Might be in the "Twins" section or the "carbs" section?

You can take the caps apart and clean them- unscrew the plug tip inside. DO IT OVER A WHITE SHEET= tiny bits inside. and try to note the order of the bits...

[fbody_mike]

Both carbs should have the screens, atleast on my GS250T both carbs have them. I am guessing they are there to help air flow and atomization of the air/fuel mix. I bet they are not that critical and probably impossible to find without getting a whole carb set or bike. The are also easy to damage if they slip slightly out why you are re-fitting the carbs to the engine, they can get bent and distorted easily.
A stuck float, causing the overflow of fuel will kill a cylinder quickly. 10 K-ohms is an ok reading for the caps too, but they do wear out and resistance isn't the only thing with these, they are cheap and easy to replace and it is a good idea to replace them. Why you have it this far apart, and since you did the valves it may be a really good time to do a compression test.

[Hamcake]

Thanks for the insight and ideas, guys!
Continuing to disassemble the carbs.
I'll see if a neighbor has a compression tester.

-Hamcake