1983 GS 450T Problem

[Rick123]

G'day

Well this 450 is killing me, It started out as an idle problem. If I give the bike a twist on the throttle, it takes quick some time for it to idle down again, and when it does idle back down, it is running at higher RPMS then before. So I assumed it was a carb problem. I pulled the carbs apart and clean them, new o-rings, and put them back together. I then hooked up a mercury sync tool and the carbs are not in sync, they are reading over an inch apart on the scale. So off again, re-clean and adjust, same thing. So I do a leak test, everything seems OK. I then get the bright idea to do a compression test..... 80 on one side, 130 on the other! So a buddy of mine says it must be rings. I pull the valve cover off, everything looks great, I pull the head off, all is good, I pull the block off, again, all is good, rings are good. So I ordered a new head gasket and while I wait for that to come in, Is there anything I am missing or thoughts on what the problem is? Would low compression cause my problem of idling down?

Thanks a whole bunch folks
Rick

[Nessism]

I'm not sure if low compression could cause the problem you noted. One thing I do know can cause that problem is air leaks between the head and the rubber carb spickets. You need to replace the large rubber O-rings sealing these two parts. Air leaks here are one of the most common problems on all the two valve GS motors.

Hope this helps.

Ed

[nabrams]

Yeah, sounds like an air leak to me. Though the leak could be anywhere in the system (airbox, boots, exhaust) - see my other posts about this.
The low compression would result in choppy/erratic idle when it finally does come down. It also could lead to hard starting if the compression is really low.
By the way the low compression could easily be a result of insufficient valve clearance between the valve shim and the cam lobe - this is the most common cause of low compression. I hope you checked that before pulling the head and block off. The second most common cause is a blown head gasket, but this rarer on the GS450.

[Rick123]

As soon as I read your post, I wish I could go back in time to check vavle clearance!!!
I will start there. I will have to order a manual. Do you happen to know what they should be at?

Rick

[bgmart450]

inlet and outlet: 0.03 - 0.08mm (0.001 - 0.003in)

[Rick123]

Now That i think about it (funny how things come rushing back to you) The valve itself was almost white inside the the head...... and so was the spark plug........ do you think this would be valve adjustment or intake leak?