Suzuki 2 Strokes

Hi guys, thanks to the info on this board I have my GT550K up and running after years of sitting in a dark corner of the garage. It was an Ebay find and was a crap shoot as far as the condition of the motor.
It starts an idles perfectly now. I'm working on sorting the jetting, I gutted the rotted stock exhaust pipes, welded in dirt bike style baffles wrapped in batting. Sounds great. I install #30 pilots, down a clip position on the needle, and started with #105 mains but now have #100s in there. Everything is working great BUT the bike has a NASTY vibration from idle to about 5K rpms. It sounds like it is coming from the cylinder area. I figure if it was crank related it would have blown up or gotten worse. It's bad, it shakes the bars and can be heard over the exhaust note!

I know it's hard to diagnose from this short description, an ideas I can try/what to check out?

Thanks, Tuna.

Remove the right side engine cover and check for play in the clutch. If the nut came loose, you would get those symptoms. There is a large nut in the center that holds the clutch hub on. Behind that nut there is (or should be) a splined washer. This is meant to be bent down over the nut to keep it from backing off. Maybe the PO had it apart and neglected to put it back in or forgot to bend down the tab.
At any rate, I'm betting the clutch ready to fall off or explode and self destruct.

Ok, I'll check that tonight. Someone has been in there, I can see the mauled up hex screws. Thank you.

Hi, if the clutch checks out OK I would suspect the wrist-pin bearings, if they fail they can make a very harsh, loud rattle and cause vibration. I hope it isn't those, but if it is, they're a pretty easy fix.

If you pull the cylinders, just replace them, check the wrist pins for wear & scoring too.

Keep us posted ...

Question for the experts: could this be due to a starter clutch failure?

Hi,

This maybe the starter clutch as it is a known problem.

Please see attached service bulletins as 1 PDF.

Please email if you need the (very bad quality) originals.

Dave
Southampton UK
GSX1400
GT550 1974, 1975 and 1976
CR250

gsx1400dave wrote:Hi,

This maybe the starter clutch as it is a known problem.

Please see attached service bulletins as 1 PDF.

Please email if you need the (very bad quality) originals.

Dave
Southampton UK
GSX1400
GT550 1974, 1975 and 1976
CR250

That looks like a lot of work! I opened the case today and inside looks new. Nobody has tampered with the clutch hub nut. After removing the clutch plates, I can see quite a bit a bit of slop. I'm betting this is pretty normal, and the starter works great. So I think I will move on.

Craig380 wrote:Hi, if the clutch checks out OK I would suspect the wrist-pin bearings, if they fail they can make a very harsh, loud rattle and cause vibration. I hope it isn't those, but if it is, they're a pretty easy fix.

If you pull the cylinders, just replace them, check the wrist pins for wear & scoring too.

Keep us posted ...

I will check this out next. I was hoping for something simple! I can see the "might as well.." syndrome kicking in (rings, bearings, etc..) LOL!

You may also want to check your primary drive gear. The J models had problems in this area and just maybe a PO has messed with yours. A loose primary drive gear will rattle and knock like crazy....and, if left, will screw up the end of the crank.
See US Suzuki Service Bulletin #GT-8 here http://www.oldjapanesebikes.com/mraxl_G ... etins.html

H2RICK wrote:You may also want to check your primary drive gear. The J models had problems in this area and just maybe a PO has messed with yours. A loose primary drive gear will rattle and knock like crazy....and, if left, will screw up the end of the crank.
See US Suzuki Service Bulletin #GT-8 here http://www.oldjapanesebikes.com/mraxl_G ... etins.html

Ok I'll re-torque that. Thanks for the advice.

The center piston has quite a bit of fore and aft movment. All the needle bearings seem good and tight. Guess it's piston slap. Tear down begins....

Before pulling it apart, it's worth double-checking the ignition timing and the carb sync ... if those are not right, the motor WILL vibrate and rattle ...

Craig380 wrote:Before pulling it apart, it's worth double-checking the ignition timing and the carb sync ... if those are not right, the motor WILL vibrate and rattle ...

Yes sir, triple checked the timing, took some doing, but it is spot on. First I used a dial indicator on each piston top. Then fine tuned with a strobe. I used the method of disconnecting one cylinder at a time and getting a perfect 1100rpm idle on each pair. I get a perfect 1700rpm idle, and it settles down right away. I also checked the exhaust temps with an infra-red. All these tips I picked up here on this forum. I'll keep the updates coming......

Mine has the same symptoms... But havent syncronized the carbs yet.

What is the original spec on the idle rpm?

How much vibration is acceptable? Mine idles fine But vibrates under 3000rpm... Also in the handlebar is that okay or is it possible to get it All smooth?