WHOA! Very Scary Problem....

J

Jfishsolevibe

Coast to Coast
so, following this thread - I going to start a new build thread for the bike I picked up today - A fantastically clean Suzuki GT380 3-cyl 2 Stroke. Bikes got 11k on it and its CLEAN. Runs and rides grreat........ or so I thought.

Had it out for its first shakedown today, and I am at a light, gave it a rev and was about to release the clutch - I had spooled it up to 4 grand and instead of coming down, it kept climbing after id let off the throttle - climbed all the way to 9000 (1000 OVER redline).... I flipped the kill switch (which id used to kill the motor several times already) and it DIDNT kill the motor!!! :eek:

I then reached down and yanked off the plug leads and it STILL didnt kill it! I ended up dumping the clutch and that did the trick ???

Am I nuts or is this is as simple as a stuck throttle cable??? It was scary as shit - because this bike is FAST and the idea of that happening while Im riding.... yikes!!


Can you guys help me figure this one out before you read about me in the paper?

Thanks dudes!

Fish
 
You probably got an airleak somewhere.
May have throttles severely mis-adjusted and also, may have 'cleaned' exhaust by riding it.
You did a full service and checked EVERYTHING before you rode it didn't you?

PJ
 
Thanks PJ - I thought airleak as well... And I have not synced the throttles -

I went over my manifolds before riding - Cinched everything up - Didnt do the WD40 test... could it be a leak at my headpipes, or is it more likely the intake manifold?
 
Intake side, or, seal behind generator.
If it smokes bad could be all the crank seals, check transmission oil for 'wet side' seal (should be level plug on clutch cover)
as with most things, havent done one since 1980's

PJ
 
Gotcha! Ill do some leak tests - im afraid of it shooting up like that again - any idea why the kill switch would not kill the motor? residual combustion?
 
The kill switch should have cut all spark at the coils - sounds like it's faulty too.

Glad to hear you're ok John
 
Thanks Rich! I pulled the spark plug leads off and it kept going!!!! Can you believe that? WTF? Haha

Rich can u PM me your number? I need some help with these valves on the 175! They're all outta synch. :(
 
Either hot spots on the pistons or plugs and / or burning oil.
Kind of turned into a diesel there for a minute.

In effect it was running like a glow plug remote control car.

Good luck with your troubleshooting and glad your OK.
That could have ended in a very nasty way.

Cheers.
 
Cibby: right on brotha thanks! - exactly what I thought - since it's a 2 stroke and those high rpms. Some residual heat cause ignition.

I'll let you you guys know what I come up with tomorrow. I just wanna ride it! :(

thanks again!
 
The "glow plug remote control car" is a good analogy. Thats what I was thinking...
Carbon build-up in the combustion chamber can glow and light the fuel like a sparkplug. But to rev up that high it had to have an air source, stuck throttle plates, cables, etc.
Hell I dunno... but I bet it scared the SHIT out of ya sittin at a light! DAY-UM
 
Yeah the reving up parts got me?
Even with "Run on" it will just tick over, not rev the shit outta itself!

Maybe a combination of air leaks, burning oil/fuel and hot spots in the cylinder.
 
Yep - definitely a combo of all of that. Just rechecked the rubber from the back of the carb to the motor and it's good and dry and cracking - I suspect this is my air leak - and the vaccum at those high revs kept it running on that air and the high heat of the then very hot and lean mixture.

Anyone know where I can find those rubber tubes? Haven't had them off yet so I can't exactly tell if they are just standard fuel rubber or some special fitment. Can I silicone/epoxy the leak in the short term?
 
Found some on the bay - 70 bucks!! YIKES! Better safe than sorry - Gonna try to hotrod it for the time being - maybe some epoxy and electrical tape?>?
 
I found these guys while looking for intake boots for my GT550, and sure enough they have them for the 380 too

http://www.vintage-japanese-motorcycles.com/suzuki_gt380_models_1972_1977_oem_carburetor_intake_boot_set.html
 
Thank you good sir! Already ordered up the ebay set - coulda saved 10 bucks here... :( Oh well! At least ill be safe? Haha

Thanks again guys - Any clues on gluing the existing ones until the new ones arrive? Can/should it be done?
 
I think Bikebandit.com has them for $12 each, if I'm reading the diagrams correctly. Their part number on it is 480698-001 (Bikebandit part number).

http://www.bikebandit.com/1976-suzuki-motorcycle-gt380a/o/m6251
 
probably not a good idea to glue them, if they fail or leak somewhere else it could be even more catastrophic
twostrokes don't tend to soft seize' like fourstroke motor
 
Actually was able to pull the boots of the extra set of carbs that came with the bike - they're in good shape - bike runs great! Zing zingg! (2-stroke sound) haha
 
I beleive honda developed a two stroke based on a combustion radical design...this is not uncommon in two stroke pipe designers where high rpm dyno runs result in the radical firing....
 
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