Post-top end rebuild issues: racing idle, hot cylinder

[oldyam80sg]

The idle big screw-did you touch that? Last year the bike was running fine then I went for a ride and the rpms once it really warmed up started to climb.I rode to a school parking lot to look at what could have caused this. You cannot ride like that as very dangerous and try to shift-forget it. I had no tools on me. I usually take a long screwdriver just in case.I used a stick to turn the big idle screw. That calmed it down. I went the wrong way when I adjusted it in the garage. With the carbs cleaned, and synced the rpms should not go up when they are warmed up. I think my 80 SG idles at just a hair under 1000 rpm and runs until I shut it off.

[Forden]

The idle big screw-did you touch that? Last year the bike was running fine then I went for a ride and the rpms once it really warmed up started to climb.I rode to a school parking lot to look at what could have caused this. You cannot ride like that as very dangerous and try to shift-forget it. I had no tools on me. I usually take a long screwdriver just in case.I used a stick to turn the big idle screw. That calmed it down. I went the wrong way when I adjusted it in the garage. With the carbs cleaned, and synced the rpms should not go up when they are warmed up. I think my 80 SG idles at just a hair under 1000 rpm and runs until I shut it off.

I did, yes, in fact I thought i had solved it exactly that way--it was racing on the center stand, and I backed off that throttle stop, which brought it to normal idle, and I ran it for some time and revved it a bunch of times, and it seemed good. Next day I started it (and it was VERY cold blooded with the throttle stop in that postion), warmed it up and took it out, and less than 1/2 mile down the road it was doing it again. Challenge to get it home safely, as you say.

I'll keep hunting, and thanks for the thoughts, keep 'em coming if you have em!

[oldyam80sg]

Did you do the bread tie sync? Those little springs should not be maxed out. If you did make sure you follow it to a T. Also is the throttle cable binding up? is there anything that is preventing the butterflies from closing? I'm thinking maybe something is bent. Once the carbs are back together, did you move them by hand and lube the springs?

[oldyam80sg]

Just doing some reading on another forum (Kawasaki) and guy had cracks where the carbs mount to. You might want to check that out. The rubber after all these years does deteriorate. That could cause your rpms to climb.