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Mid range stumble and poor high speed acceleration .... Solved

  • Thread starter Thread starter jdvorchak
  • Start date Start date
J

jdvorchak

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I've had a nagging issue with my 81 GS850G where there was an off idle stumble. Along with that was sluggish acceleration above about 3000 rpm. I've revived this former barn find with new plugs, plug caps, rebuilt carbs, new O-rings, weak charging circuit and the list goes on. I got the bike starting great and idle is smooth as can be. So today I decided to see why it performed so sluggish. Compression check 110 to 120 psi across the board. Idle mixture screws to best idle. Then it occurred to me to check the timing and the condition of the mechanical advance. Well surprise! Timing was spot on but look at the advancer:



So I pulled it and dropped it into a glass full of vinegar for about 3 hours... Cleaned up nicely and I lubed it and put it back on. Wow did that make a difference. No more off idle stumble and grabs revs to the redline like a pro. I got busy helping my brother with his camper so I haven't ridden it yet. I'll try to fix the petcock and headlight and maybe ride it tomorrow.
 
Great ! Glad you found the problem. Sure would like to see an after shot.
 
That would certainly do it, always nice to get a little timing advance going on there. Those gaskets should be available to keep that from happening again.
 
BillH said:
Great ! Glad you found the problem. Sure would like to see an after shot.
Click to expand...
Yeah I thought about that just as I was making this post. I still have more work to do on her so maybe I'll pull that cover off and take a pic. It actually doesn't look that much better but it moves freely and I was able to use my timing light to verify full advance at what sounded like about 4 or 5000 rpm. Those weights were stuck solid and the rotating part was frozen to the shaft it rides on. I spent more time cleaning the moving surfaces than the parts you see here. I need to anyway to put on a new gasket which I'll order tomorrow. This old bike is just about ready for the road. New tires and tubes, brakes, rebuilt the calipers and both MC... It's been fun! Really I enjoy bringing an old bike back to life. Amazing to me how little money you have to spend to get a really nice riding/running bike if you do all of the work yourself. I even change my own tires with Motion Pro tire irons.
 
OldVet66 said:
That would certainly do it, always nice to get a little timing advance going on there. Those gaskets should be available to keep that from happening again.
Click to expand...
If you look closely at the 10 or 11 o'clock position you can see where the gasket looks like it was deformed when it was installed. Probably been like that since 1981.
 
Got the new gasket on order from the local dealer. Took it for a short test ride. Wow does it pull hard now all the way to red line! After I synced the carbs this is the smoothest idling bike I've seen in years. I'm happy.
 
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