symtoms of a catastrophic failure?

[pnaberhaus]

With the spring riding season starting here in SW Ohio, I thought I wake up the ol' '89 GS from its winter hibernation. Nothing unusual to anticipate once again as I have been doing this every spring since I bought the bike in 1992.

After installing a fully charged battery that had been on a battery tender on-and-off all winter, the bike started right up and after the usual cold hiccups and occasional cough, it settled into a normal idle as I gradually closed the choke.

With the bike now warmed up, I slowly rode off, shifting gently into second and then third gear. After 4/10s of a mile, with the throttle barely open, all of a sudden the rpm went to 7K and did not respond whatsoever to any manual throttle input. I immediately hit the kill switch and coasted to a stop, shifting into neutral as I slowed.

Now safely stopped on a quiet residential street, I set the engine off switch to start, turned the key off, then switched it on again. The engine turned perhaps once and then.....a very loud backfire.(after I pushed it home, my wife said she heard the backfire, thinking someone discharged a firearm).

Trying to restart again after the backfire resulted in absolutely no response whatsoever from the engine. Nothing turned over, no sound at all,  not even the ominous "click-click-click-click" of ignition failure.

I have been riding for 50 years and have owned two Triumphs, two Hondas and this GS500E. I've never encountered a failure of this nature. Any thoughts on cause and result? Where to start a diagnosis? The oil is clean and fresh from last year and when I last rode late last fall, all was fine. The mileage is only 7760.
Any advice, suggestions or other help will be greatly appreciated.

Paul

[Big Rich]

Hmmm.... that's a tough one. It "almost" sounds like the clutch is way out of adjustment and slipping (since it revved to 7k rpm). But if you let off the throttle it should have dropped back down.

Now the only way for the engine to rev that high is with the throttle open - so I'd say something stuck. Throttle tube, throttle cable, butterfly valve linkage, etc.. Because it revved high and you hit the kill switch, could that have dumped some gas into the exhaust which exploded once it was restarted? I'm just guessing on that one.

I don't know what could have been damaged from a massive backfire though. Maybe try turning the engine by hand to make sure nothing is locked up, then do a compression test if it is free or a leak down test if it's not.

[sledge]

Here is a suggestion, I have heard of backfires forcing the engine to turn a few degrees backwards against its normal direction of rotation. Maybe yours has done this and perhaps locked up the starter clutch or caused the timing chain to jump a tooth. Hopefully the bang wasn't big enough to damage a valve or piston crown or bend a rod    You are going to have to pull the covers off and investigate.

As for the engine runaway, gotta be something in the carbs or a seized cable/linkage

[lucas]

Tldr; I don't think the backfire is a symptom but normal behavior for being shut down at 7k rpm.

The other day I learned that turning the engine with the kill switch engaged will cause a backfire.

I was rolling through a residential neighborhood and as I passed a bicyclist I thought I would hit the kill switch to save her from breathing my partially combusted hydrocarbons and partially to spare her the loud exhaust.  I was on a gradual downhill so I coasted along for a while with the clutch pulled in.  I let the clutch out expecting it to bump back to life but to my momentary worry the engine did not fire back up... Then I remembered I had flipped the kill switch.  Unflipped it, let the clutch out, and BANG.

So perhaps when you hit the kill switch the momentum of the spinning engine drew fuel into the combustion chamber and into the exhaust.

The GS500 has a "wasted spark" ignition which means that both cylinders spark together.  So when one side is combusting fuel the other side might have it's exhaust valve open.

[pnaberhaus]

Yes, I know this thread is 5 months old but I thought it would be informative and amusing to share with the forum members what the problem turned out to be.
In the air box/cleaner, the carbs, the intake and even the cylinders, there was........friggen' CORN. Corn had literally clogged up everything on the intake side of the bike. Having lived in this same house for thirty years and having kept this '89 GS in the attached garage since 1992, there has never been a mousey problem. My old 1970 sports car has never evidenced any infestation, but somehow mousies had decided to warehouse their food stores in my bike. I suppose what caused the incredibly loud backfire was.......popcorn

Paul

[ShowBizWolf]

    

This is an awesome update 

[Shepa]

ROFL!!!



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[Janx101]

Bit the mousies would have starved!

[qcbaker]

That is the funniest "engine failure" story i've ever heard... Once you cleaned all the corn out, did the bike start/run?

[rscottlow]

Haha this is great. In what part of southwest Ohio are you located?


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[pnaberhaus]

That is the funniest "engine failure" story i've ever heard... Once you cleaned all the corn out, did the bike start/run?

The top end is off, and of course intake and carbs as well. Getting cleaned and waiting on parts.

Paul

[pnaberhaus]

Haha this is great. In what part of southwest Ohio are you located?


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Scott, I am in the Loveland/Miami Township area. And you are where in the Cincinnati Region?

Paul

[rscottlow]

Haha this is great. In what part of southwest Ohio are you located?


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Scott, I am in the Loveland/Miami Township area. And you are where in the Cincinnati Region?

Paul

Ok cool! I'm near Hamilton.


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[user11235813]

symtoms of a catastrophic failure?...

If you see your spleen sliding down the street.