jsmits
CB750 New member
I recently purchased a '78 CB 750 from a local. The thing starts right up and runs after some minor adjustments to the choke and idle screw. After warming up, it runs pretty well, but I have been unable to take it for a drive yet. I'm working on it with a friend, and we were able to accelerate through all 5 gears up on the stand with little trouble, but there's an idle down issue that we need to resolve before any attempts at riding it are made...
The main trouble I'm having is with the throttle and, what I believe to be consequently, the idle down. You see, the idle seems to stick, almost like the carbs aren't closing all the way. Except... they are. We've already taken the covers off the tops of them and the little pistons all line up and fall evenly. The problem is that the bike does not rev back down from around 3500-4000 a lot of times. I don't know a lot about carbs, throttle, and idle, except what my dad taught me working on the old 90's Arctic Cat's. If we push down on the throttle pistons while it's idling high, it will idle down a bit, but we usually can't get it to properly idle back down to ~1500 unless it's gunned and then the throttle is let completely loose, allowing it to achieve a full motion and some momentum on the way back down.
The throttle cables seem to have been rerun recently. Some low-slung, cafe-style handle bars were put on. It looks like the the old switches and throttle were then put back onto these aftermarket bars. The throttle is really stiff, you can feel it rub on the bar. The bike has sat for at least two years, so we've been lubing everything as we go, and it's loosened quite a bit, but we're pretty sure it's a combination of the throttle friction, and possible the throttle mechanism that opens up all 4 carbs in unison. We also think the ignition points might have something to do with the problem as well.
We haven't tried much yet, and this is just our gatherings after a few hours in the garage. What do you guys think? I'm eager for some insight!
Thanks ahead of time to anyone who might be able to point us in the right direction. Cheers!
The main trouble I'm having is with the throttle and, what I believe to be consequently, the idle down. You see, the idle seems to stick, almost like the carbs aren't closing all the way. Except... they are. We've already taken the covers off the tops of them and the little pistons all line up and fall evenly. The problem is that the bike does not rev back down from around 3500-4000 a lot of times. I don't know a lot about carbs, throttle, and idle, except what my dad taught me working on the old 90's Arctic Cat's. If we push down on the throttle pistons while it's idling high, it will idle down a bit, but we usually can't get it to properly idle back down to ~1500 unless it's gunned and then the throttle is let completely loose, allowing it to achieve a full motion and some momentum on the way back down.
The throttle cables seem to have been rerun recently. Some low-slung, cafe-style handle bars were put on. It looks like the the old switches and throttle were then put back onto these aftermarket bars. The throttle is really stiff, you can feel it rub on the bar. The bike has sat for at least two years, so we've been lubing everything as we go, and it's loosened quite a bit, but we're pretty sure it's a combination of the throttle friction, and possible the throttle mechanism that opens up all 4 carbs in unison. We also think the ignition points might have something to do with the problem as well.
We haven't tried much yet, and this is just our gatherings after a few hours in the garage. What do you guys think? I'm eager for some insight!
Thanks ahead of time to anyone who might be able to point us in the right direction. Cheers!