Possible fried exhaust valve?

[The Buddha]

You have a bad valve (like bent/broken etc) it wont even run in that cyl.

Your issue likely is with carbs and hoses (sorry to say) once you've eliminated the intake air leaks etc.

Cool.
Buddha.

[gsJack]

Before you tear it apart check to see if it's running on one cylinder like you suggested in the first post above and which one it is.  If it will idle pull off the plug wires one at a time to see which cyl it's running on.  If you pull off one plug wire and it stops and put it back on and pull off the other and it keeps running you'll know which cyl it's running on.  I'm still thinking electrical, maybe ignition coil or pickup coil or module.  But even if it's a fuel problem you'll know which cyl it is.

[Wagoneer]

I double checked again and it still is running on both cylinders, it's just starving itself of gas. This was proven by both plugs showing extreme lean conditions and both of the float bowls only having a few drips of gas in them when the bike starts stuttering. I ruled out ignition when checking for sparks when this happens and there's plenty of spark.

This has turned into just a full blown mid-season maintenance job. While I have everything apart I'm going to completely clean the carbs, replace the float needles, check the float heights again before taking them off, chek the valve clearance again since it's the perfect time to do it, and rejet the carbs. I've been meaning to rejet them anyways since my plugs have always shown that I'm running slightly lean. So I ordered 20/65/145 jets for my setup. I've had a K&N lunchbox sitting on the shelf waiting to be installed for a while now too. I was hoping to do all of this stuff after the season was over but looks like I'll be doing it mid-season. I have having the bike down during our tiny riding season up here but I have no choice.

What bothers me is that so far I have found nothing physically wrong. So hopefully when I tear apart the carbs it'll be something obvious. Before I remove the carbs I'm going to double check again for any intake leaks to rule that out.

[The Buddha]

OK is the tank venting ? And are the carbs venting. The upper top T in the back should have a hose that is clear and open to atmosphere.
Cool.
Buddha.

[Wagoneer]

OK is the tank venting ? And are the carbs venting. The upper top T in the back should have a hose that is clear and open to atmosphere.
Cool.
Buddha.

Yes, the tank is venting. I took the cap completely apart and cleaned all the holes and vents. It wasn't dirty at all, but I took a guitar string and made sure all the holes were clear anyways. I even hooked up a hose to the float bowls (I did this to both to make sure) and drained about 1L of gas through the float bowls with the petcock on prime. That's way more gas than I'd use in 10min of riding, not to mention flowing much quicker. There was zero pressure released when I opened the tank afterwards.

But here's where it gets interesting. I checked the valve clearance, and my left exhaust valve can fit a .152mm feeler gauge in it (.17 does not fit). How does this happen? Aren't valve clearances supposed to get tighter over time? I know you're supposed to run the exhaust valve clearance a little loose at .1mm but isn't .152mm a little overkill? I may have overlooked this because last time I tested clearances I was specifically testing for tightness, so I may not have actually tested what the clearance actually was. The intakes are both between .03 and .07 and the right exhaust valve is between .07 and .1mm. The shim in the left exhaust valve is a 2.6. So do I need to run a 2.7 to be back in spec? Could running the exhaust valve so loose cause any damage other than to the cam lobe? Because the cam lobe as no scoring or discolouration at all.

Anyways, I also picked up some used plug wires/coils to try out just in case that's the issue. Luckily I can return them in case it doesn't end up being the issue. Are these things really worth $150? This was the cheapest I couldn't find these stupid things at local yards in Canada. I found 3 places that had them locally and the other two wanted $200 for the set. This seems ridiculous to me?

I also found that both of the airbox boots going to the carbs didn't have any bolts in the clamps. So they weren't even clamped on. I tested the carb side going in the engine for the leaks but I never thought to test the airbox side. Maybe this is my lean issue?

I seem to be slowly fixing all the ridiculous things the previous owner did...

[gsJack]

I set exhaust valves at .003-.005" (.08-.13 mm) and intakes at the Suzuki .001-.003" spec.  I've changed exhaust valves to smaller shims only, none ever got wider gaps.  And after 80k miles on my 97 and 100k miles on my 02 the intakes still had the shims that came in them.  I'd put a larger shim in that left exhaust of yours to bring it into my spec, I feel that I've been streching it far enough.

The carb vent hose from the upper T is run back and down between the air box and battery out of the wind.  It should be open to the atmosphere but placed so it can not be affected by high cross winds.

[Wagoneer]

All valves are officially within spec! Both exhausts are at ~0.10mm and the intakes at ~0.05mm.

Both new coil packs/plug wires are replaced and new spark plugs in. Just waiting on the new jets to finish up and I can finally start buttoning it up. I HOPE this clears up the problem.

If it doesn't, I guess the CDI box is all that's left to replace.

[Wagoneer]

Update: It has to be the CDI box. After I've done everything I possibly could it's still doing it. This time in about 5min of riding and it's above 30deg C out today so it's definitely heat related. At least the salvage yard said if it wasn't the coils I could bring them back in and use the credit towards a CDI box. So that's what I'll be doing tomorrow morning. Luckily it did it right outside my driveway so I quickly grabbed a hose and checked the float bowls and there was plenty of gas in both. Definitely ignition related.

On a happy note, the bike fired up on the first try after my first time rebuilding, rejetting and cleaning carbs! All I had to do was adjust the idle back up to where it should be. And boy does it sound different with the lunchbox compared to the stock airbox!

[gsJack]

How about the pick-up coils, have you checked them?

[Wagoneer]

How about the pick-up coils, have you checked them?

Yes. 6.4/6.2 ohms cold. Should I check hot as well? I can't find the plug to check the other side of the harness though. None of the colours seem to match up to what's on the pick ups.

And my coils are both at 5.1ohms testing right at the contacts.

[Wagoneer]

So I just finished giving myself a crash course in checking resistances in ignition systems and everything checks out perfect from everything to the pick ups to the spark plug boots.

So all hands are pointing towards the CDI box simply overheating.

[EdChen]

I thought there was spark when the issue happened? Maybe I'm wrong, but I assumed the CDI box had something to do with the spark. Either way, I hope you get it figured out! Intermittent issues are the worst!

[Wagoneer]

Remembering back I think I only tested spark after the bike cooled back down and I was troubleshooting. I was under the assumption back then that if it was spark there should always be spark.

I never had the tools with me to pull the plugs whenever it happened.

[The Buddha]

Oh yea losing 1 cyl or both cyls when warm = trigger coil - under that round cover by your right foot.
Cool.
Buddha.

[Wagoneer]

Oh yea losing 1 cyl or both cyls when warm = trigger coil - under that round cover by your right foot.
Cool.
Buddha.

You are correct. Here I am stuck on the way to work again. I guess I didn't ride it long enough the other day to find out if it was really fixed.

As soon as I get home in checking the resistance for the pick ups to see if they're screwed up at temperature but fine when they're cold. It's my left cylinder that isn't firing.

And hopefully I can return my new CDI box for a set of pick ups. I've already returned my coils for the CDI.

[Adshed]

Did you end up finding a solution the problem?

[Wagoneer]

Did you end up finding a solution the problem?

Yes! It was the pick up for the left cylinder. It checked out fine when it was cold but then failed once the heat from the engine bled into the pick ups. I actually couldn't find any dual pick ups from '89-'02 GS, only single pick ups from new GS's. So I made one dual pick up out of two single pick ups and she works perfectly again.

The silver lining, in the process of trouble shooting I finally upped my jets, did a valve clearance, and she's running even better than before now. And I learned a lot in the process!

[Adshed]

Ahh, great to hear. Thanks for sharing!

[gsJack]