Bad stator?

[nit]

I bought a 1999 GS500E that has been running poorly ever since I bought it. The main symptoms are misfires and subsequent stalling when the bike starts to warm up (3-4 minutes after starting with choke still on). I assumed the problem was in the carbs, so I rebuilt and rejetted those. I haven't properly synced them yet, but so far there's no indication of improvement. Today I drained the oil and pulled the left crankcase cover to check the notorious starter clutch. First thing I noticed is that the stator looks cracked and crispy. Pictures are attached. So here are my questions:

1) Based on the pictures, is the stator bad? Or do they normally look like this?

2) Could the bad stator be the cause of my problem? (Misfiring and stalling while warm, seems to be primarily on the right cylinder) If not the stator, any other ideas?

3) If I need to replace the stator, can I leave the engine without oil for a few weeks while I wait for the part to arrive?

Thanks. Appreciate any help.

[nit]

One more question: The fly wheel bolt seems really tight. Is there any way to check the starter clutch bolts (the ones that come loose apparently) without removing it? Thanks!

[herennow]

Hi, welcome to the forum.

That brown grunge in the case looks very suspect. I'd guess that the crankcase had gas in it which can dissolve the potting around the coils. The bare wires are visible on the left. I'd reuse everything.

If your battery charge is OK, then the stator is working, you can check what the voltage is when the bike is running and make sure. If your battery is at the required 12.6 Volts than the stator should make not difference to the running of the bike. If the battery is not being charged by the stator/reg-rec the bike will run fine until the battery runs flat but you should get about an hour of running from a good charged battery.

I'm a real proponent of not buying anything too quickly. I've wasted too much money that way when the problem was elsewhere. I'd reuse the stator as is, might one day fail due to vibration on the exposed wire but that could be very far in the future. However, another concern is that if the bike was run with gas in the oil your main and big end bearings can get damaged from the diluted oil. (note gas should only leak if the bike was left on "prime" AND you have a leaking carb needle valve or valve seat).

RE the stalling- if the bike starts ok and runs for 4 minutes and then stalls with the choke still on, I'd say its much too rich. I switch the choke off after a minute.  What happens if you switch the choke off after a minute or two - still stalls?

When an engine is cold it needs more gas to run but as it warms up that same initial rich gas ratio is too rich and the engine needs a leaner mixture. If an engine runs well while cold and badly when warmed up, that's generally a symptom of too rich. Did you check float level (or easier, the fuel level using clear tube?), while carb was apart did you check all jets for correct size? and location? (folks can swap jets around or use incorrect jets while previously jetting). What did you rejet the carbs to?

My money would be on a leaking needle valve or a very high fuel level making bike too rich. Possibly a leaking needle valve seat, but this is rarer.

That bolt is pretty tight. A helper can lock the back wheel with the brake to help undo it. I block the pistons by getting them to the bottom of travel and feeding a long length of nylon rope into the chambers through the spark plug hole. Its soft and the pistons lock against it without damage as they try to move up. Tie a knot on the end of the rope to prevent it falling into the chamber.

I forget if you can check the bolts with rotor still in place. Someone will add this. Note you will need a special bolt to pull the rotor off the end of the crank and must replace it very securely or the rotor can spin the stator. I'd leave it if I'd not heard any rattle.

Good luck.

[nit]

The crankcase most likely had gas in it. When I rebuilt the carbs, the right carb flooded gas into the airbox. I assume some also got into the crankcase. I pulled the carbs again, replaced the needle seat, and readjusted the float level. No gas in the airbox since. I'll try double checking the float heights tomorrow with the clear tube method. The gas should be level with the top of the bowl, right?

If I turn the choke off, the bike hovers around 1k rpm and eventually dies anyway. Maybe a sync/idle speed issue? That would also imply that it's not running too rich, right?

Carbs were jetted to 40/125 with 3 turns out on the sir screws, as per the wiki.

Not sure about whether the battery is charging, since it hasn't been running well enough to ride it anywhere. I've got a battery tender, so the battery is kept fully charged. I'll hold off on buying a stator since it doesn't seem to be the cause of the misfiring/stalling.

Thanks!

[herennow]

Does it still die if you give it a little bit of throttle? If so you can just adjust the idle speed, but this should be done when fully warm. You can get it to idle correctly when cold and then just stop every few minutes to check the idle and adjust as necessary.

[mr72]

I think a 40 pilot and three turns out is probably too rich. Did you adjust it in-situ or just set it static?

As usual, try this:
https://joshkarnes.blogspot.com/2017/09/fixing-common-gs500-carburetor-issues.html

It can't hurt to turn the pilot needles in 1/2 turn and see if the problem goes away. Also it could be leaking fuel around the pilot needle o-rings, which are often overlooked, in which case it will run rich all of the time no matter where you set the needles.

Have you checked the compression? This problem sounds to me like zero valve lash (valves aren't closing, insufficient clearance), bent valve, carbon build-up on valves, or the rings are shot, or all of the above. When it gets warm and won't idle will it keep running if you keep the revs real high?

And another problem someone will certainly bring up is maybe the signal generator (hall effect sensor that triggers the spark) is going bad and manifests as not triggering at high temps. You can easily check this with an ohm-meter. Take the right side signal generator cover off, start the bike and get it to the point where it dies and then measure the resistance of each pickup real fast as soon as the bike dies. Don't worry about the measurement, if it's <1K ohms then it's good, if it's open circuit then it's bad.

[nit]

Does it still die if you give it a little bit of throttle? If so you can just adjust the idle speed, but this should be done when fully warm. You can get it to idle correctly when cold and then just stop every few minutes to check the idle and adjust as necessary.

I'll try playing around with the throttle some more. I can usually "catch" it with the choke or throttle before it dies while idling, although the last time I took it for a ride it died even with throttle and I had to wait 5 min before I could start it again. Did this 3-4 times dying every 20 min or so and needing to wait 5 min. At that time it seemed like a fuel issue so I rebuilt the carbs.

I think a 40 pilot and three turns out is probably too rich. Did you adjust it in-situ or just set it static?

Static so far. I'll try closing the screws half a turn and see if that improves things. I replaced the o-rings when I did the carbs, so I assume they are not leaking.

Have you checked the compression? This problem sounds to me like zero valve lash (valves aren't closing, insufficient clearance), bent valve, carbon build-up on valves, or the rings are shot, or all of the above. When it gets warm and won't idle will it keep running if you keep the revs real high?

I haven't checked compression, since I don't have the tool. Valve clearances are good. I'm running the intakes within spec and the exhausts a little loose per this forum. I haven't tried holding the rpms high. Would that indicate the valves are bad or good? Really hope it's not a valve/compression issue, since I'm not sure I have the know-how to do a top end rebuild and I definitely don't have the money.

And another problem someone will certainly bring up is maybe the signal generator (hall effect sensor that triggers the spark) is going bad and manifests as not triggering at high temps.

Good idea on the signal generator, I'll give it a shot.

Appreciate all the help. It might take a couple weeks to try any of this though, since I'm waiting for a replacement generator cover gasket.

[mr72]

although the last time I took it for a ride it died even with throttle and I had to wait 5 min before I could start it again. Did this 3-4 times dying every 20 min or so and needing to wait 5 min. At that time it seemed like a fuel issue so I rebuilt the carbs.

This is EXACTLY what mine did with bent valves. FYI.

I replaced the o-rings when I did the carbs, so I assume they are not leaking.

OK, as long as you're good to go on that. But you need to set the idle mixture correctly which involves first warming it up completely and then closing the throttle stop and adjusting the pilot mixture screws for maximum rpm at idle. Unfortunately that requires you to be able to have the bike idle when it's fully warmed up, which it sounds like yours won't do. The idle mixture would only cause this if it was WAY too rich or lean, but my bike will idle with the pilot needles all the way in or backed out to 4 turns. It just won't idle BEST in those cases. Hard to figure what carb issue would cause this behavior. I think it's valves, hate to say.

I haven't tried holding the rpms high. Would that indicate the valves are bad or good?

Just going from personal experience, when my bike had bent exhaust valves, it would run fine for the first 10-15 minutes and then die if you let it idle, wait for it to cool, run again, die again, etc. But if I kept the revs above abut 7K it would run without dying. Of course it's basically impossible to ride this way. I had to trailer it home after walking it about 5 blocks to my parents' house (I was out riding with my dad at the time so we were near his house). And then I rode it to a shop 5 minutes away and handed over my wallet.

Really hope it's not a valve/compression issue, since I'm not sure I have the know-how to do a top end rebuild and I definitely don't have the money.

Me too. But in retrospect I wish I had done my top end rebuild myself. I certainly could have. It's just that I (like you) thought it was a carb issue and I had already worked my butt off on the carbs to no avail (because it wasn't a carb issue) but I was at my wits end so I took it to a shop, after they determined it wasn't carbs and did a compression check, I figured might as well let them finish the job. That was a mistake in retrospect, because not only did they take two freaking months to do the work but they also charged me about $300 more than the quote and the bike had a half dozen other things screwed up when I got it back... like, you might wonder how I know it will idle with the pilot needle screwed all the way in? There ya go. And I can tell you exactly how long it will run with the petcock vacuum line disconnected. Anyway.

I think the job's pretty easy, hardest part is pulling the carbs which you already know how to do. Then it's just a matter of staying organized and following instructions. Oh, and hiring out the machine work. Pull the carbs, pull the head, send the head off to a shop to have a valve job done, pull the jug, clean up pistons, hone the bores if needed, measure, replace the rings, put it all back together and don't get the cam timing off. I've done this myself on a car engine. I would do it again myself without hesitation on either of my bikes.

Good idea on the signal generator, I'll give it a shot.

Worth it just to rule it out. And you will rule it out, I'm 99% sure.

Appreciate all the help. It might take a couple weeks to try any of this though, since I'm waiting for a replacement generator cover gasket.

Where are you located? I wish more of you guys were around Austin, I'd love to be able to help in person.

[nit]

So it sounds like the first thing I need to do is a compression test and figure out where the problem is. If it is the valves, is there anything I can do without removing the engine, or is the only solution to take off the cylinder head? Is there a good guide to doing the rebuild, including what tools/parts I'll need and pitfalls to watch out for? Never attempted anything like this before.

Also, what's the cost/benefit analysis on just buying a used engine and swapping it out? Is there a better place to look for stuff like this than ebay?

Thanks for the offer to help. I'm in the SF bay area though, so probably a little too far.

[Kilted1]

So it sounds like the first thing I need to do is a compression test and figure out where the problem is. If it is the valves, is there anything I can do without removing the engine, or is the only solution to take off the cylinder head? Is there a good guide to doing the rebuild, including what tools/parts I'll need and pitfalls to watch out for? Never attempted anything like this before.

Also, what's the cost/benefit analysis on just buying a used engine and swapping it out? Is there a better place to look for stuff like this than ebay?

Thanks for the offer to help. I'm in the SF bay area though, so probably a little too far.

Buying an entire used engine is certainly an option.  But you have no guarantee (beyond the seller's say-so) that it's any good at all let alone better than what you have.

[herennow]

 In the us you can rent a compression tester for minimum cost from the parts stores. Remember WOT while doing it.
Bent valves are very rare, I'd suggest checking the simple stuff first. Could be fuel starvation. Make sure the vent on the tank is clear to allow fuel to run out. If not, bike stutters after 5 minutes and dies.
the easy way to check this is to attach a hose to the carb drain, put the tank on Prime and open the carb drain, you should get around 200 milliliters per minute per side.