2006 GS500, about 26k miles.

Runs well for about 10 minutes then stalls suddenly. I try restarting and the starter motor sounds fine but it won't turn over. Pull the plug and no spark. Let it sit for 30-60 minutes and starts right back up.

Just replaced the battery, spark plugs and ignition coils and still the same. Not sure where to go from here...

(Continuation of a previous thread here: http://gstwins.com/gsboard/index.php?topic=70532.0)

Testing the voltage between the battery positive terminal and the engine block shows it hover around 12.6v before the reading starts bouncing around. I get a good reading between the battery terminals.

I'm not very mechanically inclined and I'm trying to find my Haynes manual. Where are the fuses located on this bike?

There's only one fuse (and a spare fuse) on the bike. So if anything else electric works, it's not a fuse problem.

You've replaced the coils? With what? Like I said earlier, newer oem coils are usually good for a long time. I don't know what else could overheat..... have you inspected the wires from the signal generator on the right side of the crank and followed them up to the black box?

Have you checked your valve clearances recently?  Over time valve clearance reduces until the valves will barely close.  When the engine is hot the valves get longer due to thermal expansion making it so that the valves do not close at all and the engine loses compression.

This is probably why you are able to restart the engine after letting it cool off for a bit.

If your valves are out of spec when you get them fixed up you will notice a dramatic improvement in the way the engine warms, idles, and runs.

Thanks guys. The valve clearances definitely need to be checked soon. But I'm definitely not getting spark post-stall, so there's some issue in the ignition circuit. I am getting spark after it cools down.

Really strange. I'm worried about the readings I'm getting between the battery's positive terminal and frame/engine housing. It seems like a poor ground might cause an issue like this?

Do you know where the ground connection coming off the negative terminal is supposed to be?

Rich: I replaced the coils with newer OEM ones. It was cheap to rule out and I had read about others with similar symptoms leading back to the coils. 

I'm almost positive the ground wire goes from the battery to the rear of the engine. When you get that 12.6v reading between the frame and battery, what are you getting straight across the battery terminals? If its only 12.7v, I wouldn't worry too much. 

I'm getting just under 12.7 across both terminals, but the reading jumps around between + terminal and engine frame. Maybe bad connection, or my multimeter isn't working. I'll try finding that ground connection in the morning, and see if shorting the - term to the frame makes any difference with the voltage reading.

Signal generator coil developing an open circuit when warm and rectifying itself as it cools.

You can either.....substitute the part with a known good one and see if the problem disappears....or....take some readings across the coil when cold and another as soon as the bike cuts out....or.....take the parts off the bike, take some static resistance readings, warm them in an oven, take another set of readings and compare them.

Another trick, something I have read about but never tried is to hit the coil with a blast of compressed air as soon as the bike dies, the idea being to cool it. Then see if it restarts.

You wouldn't be the first to suffer this problem, its been mentioned many times in here.

Quote from: lucas on May 20, 2016, 10:14:47 PM
Have you checked your valve clearances recently?  Over time valve clearance reduces until the valves will barely close.  When the engine is hot the valves get longer due to thermal expansion making it so that the valves do not close at all and the engine loses compression................................

Valve clearances increase as the engine warms.  Steel valves expand but aluminum head expands more lifting cams away from the buckets.

+1 to Sledge post.  It acts like a bad coil so if it isn't an ignition coil it's probably the pickup coil.  Only one pickup coil on your F model.

That makes sense since aluminum expands more than steel.  So I guess tight valve problems tend to make bikes stall when cold but not after it warms up?

I'm getting 4-5 ohms from the disconnected negative lead to engine housing near the spark plug. That can't be right, can it?

Here's the negative terminal lead:

https://imgur.com/a/zIDSd

I have no idea how I'd clean the connection in that second picture without replacing it.

Does anyone know where the chassis/engine ground connection coming from the battery's negative terminal is (2006 500F)? Nothing in Haynes that I can find about it.

So I naturally misread my ohmmeter at first so nevermind about all the bad ground stuff.

But it looks like sledge got it with the pulse generator coil. Tested in range before ride, now has extremely high resistance after it stalls. +1

Based on the location of the coil, I guess it's likely to overheat again if I replace it. Possible too that I damaged it from running for several hours a quart low on oil...

Out of curiosity how did you test it after it stopped? I have not really done any electrical testing before but have a similar problem to you after long rides.

I was going off the Haynes manual. For later models: "Trace the pulse generator coil wiring back from the right-hand side crankcase cover and disconnect it at the 3-pin connector. Using a multimeter set to the ohms x 100 scale, measure the resistance between the brown and black/blue wires on the coil side of the connector." I didn't disconnect, just measured from the back of the connector. Looking for 250 to 420 ohms. For me, the connector was a little forward and left of the rear wheelwell.

Ok cheers

Jimbob, not sure what model/year you have, but you should see a white three-pin connector on the left side (accessible if you remove the seat and aft the battery) that looks like http://i.ebayimg.com/images/i/131260089529-0-1/s-l1000.jpg which is plugged into a black connector. Shove some multimeter pins into the brown and black/blue wire connections.

does it matter which pin i put the black/red pins of the multi meter and did you unplug the battery first? Also mine is an 04

It doesn't matter. Just keep in mind that you'll likely get a good reading like I did when it's cold so you'll probably have to wait to test until it stalls again.

Ok thanks for your help

I'm glad you got this figured out. I also had ignition coil or its wiring go bad and its the most annoying thing. Hard to diagnose as well.