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Just rebuilt top end of my '81 GS850. I had her running before this rebuild. I lapped the valves, honed the cylinders, replaced all gaskets. After the valve job the valves' clearances are out of spec (no clearance at all) and I'm waiting for new shims to arrive. While I wait for new shims I decided to try to start the bike, even though I know the valve clearance is wrong. What I notice, aside from the bike not starting, is that the cylinders are NOT getting the gas/air mixture. Spark plugs are getting spark but are bone dry after attempting to start. I removed the air filter pods and notice lots of gas in the carb intake. With the air filters off I hit the starter button and notice the slides are NOT moving but gas is being pushed out towards the absent air filters. The cylinder head intake boots are old but worked fine when I had her running. Would the valve clearance issue prevent gas from getting to the cylinders? The carbs sat (with gas in them) for a couple weeks while I rebuilt the top end. Should I tear down and reassemble the carbs while I wait for new shims? Any ideas as to why the cylinder aren't getting gas?
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You could be hanging valves open and not getting any suction. Do a compression test. As for the fuel coming out of the front of the carb, I have that minor issue with the carb seat not seating. I'm thinking of adjusting my floats so they seat a bit sooner, but I have fuel that comes out of the brass nipple on the right side of the carb throat. -
I was kinda thinking the same thing with regard to the valves. I'll do a compression test and report back. With there being no clearance the valves are more than likely staying open and preventing the necessary suction to bring gas into cylinders. There appears to be plenty of gas getting to the carb throat though. When I hit the starter button and the engine starts cranking I can see the gas coming out of the needle jet with the air filters off.Originally posted by 81GS850 View PostComment
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Yes, the valves settled deeper into their seats after the lapping job, and that is why there is no clearance. So the engine is now "blowing" instead of "sucking". You will get low compression readings because you have zero valve clearance and the valves are definitely slightly open. Your fuel delivery is working, but the fuel is getting blown outwards instead of being sucked inwards like it should.1981 GS850G "Blue Magic" (Bike Of The Month April 2009)
1981 GS1000G "Leo" (Bike Of The Month August 2023)Comment
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Thank you. I was looking for consensus and I do believe I have found it. I'll reply with an update once the new shims have arrived, installed, and tested.Originally posted by 2BRacing View PostComment
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Much better for them to be loose than to be too tight!
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Best way to order a really thin shim.. Or have maybe a machineist make you one for checking purposes? There's a "shim club" under one of the tech sections. You can get them for the price of shipping.Comment
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Cowboy Up or Quit. - Run Free Lou and Rest in Peace
1981 GS550T - My First
1981 GS550L - My Eldest Daughter's - Now Sold
2007 GSF1250SA Bandit - My touring bike
Sit tall in the saddle Hold your head up high
Keep your eyes fixed where the trail meets the sky and live like you ain't afraid to die
and don't be scared, just enjoy your ride - Chris Ledoux, "The Ride"Comment
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