canorthup
CB750 Member
1979 CB750K
I think I know a couple of things to check, but I just wanted to write here in case there is an easy issue or solution.
Okay, here is what happened when I originally got the bike: it would randomly go up to 4k rpm during idle. I assumed it was a vacuum leak. The rubber was original and had dried and cracked, going in and out of the carb. I had replaced it in the past on some CB550s, and almost all issues went away. So I tried my luck there. Once replaced, I used the digisync to sync them. No luck issues stayed. I completely dismantled the carbs (except where the felt is), gave them an ultrasonic bath, and used guitar wire and a generous amount of carb cleaner. Reassembled, and now the bike idles great, except the idle will, at some point in the ride, stick at 3k rpm. If I hold the brake and almost engage the friction zone, I can idle at 1500 rpm (so people don't think I am rev bombing them at a stoplight). So basically, once it sticks at 3k rpm at idle, it does not stop until I shut the bike off for a bit, then the whole process starts again. I am guessing something is sticking in the carb? I only bench-synced the carbs since their bath was unsure if the effort was worth it until I figured out the issue. I could check for leaks? I don't know
I think I know a couple of things to check, but I just wanted to write here in case there is an easy issue or solution.
Okay, here is what happened when I originally got the bike: it would randomly go up to 4k rpm during idle. I assumed it was a vacuum leak. The rubber was original and had dried and cracked, going in and out of the carb. I had replaced it in the past on some CB550s, and almost all issues went away. So I tried my luck there. Once replaced, I used the digisync to sync them. No luck issues stayed. I completely dismantled the carbs (except where the felt is), gave them an ultrasonic bath, and used guitar wire and a generous amount of carb cleaner. Reassembled, and now the bike idles great, except the idle will, at some point in the ride, stick at 3k rpm. If I hold the brake and almost engage the friction zone, I can idle at 1500 rpm (so people don't think I am rev bombing them at a stoplight). So basically, once it sticks at 3k rpm at idle, it does not stop until I shut the bike off for a bit, then the whole process starts again. I am guessing something is sticking in the carb? I only bench-synced the carbs since their bath was unsure if the effort was worth it until I figured out the issue. I could check for leaks? I don't know
