'71 cb750 carb question from Newbie

[Silvertire]

I just finished a carb overhaul on my CB750 K1. After reinstalling, the engine fires up great but is running WIDE open. I've checked the chokes and slides for proper orientation - all good. I've checked and re-tightened the hose connections at the engine and the air box. I also, disconnected the throttle cables. The slides appear to be all the way closed. Any ideas???

Thanks,
Silvertire

 

[drgnrdr750]

Have you synced the carbs? If not then loosen up the adjustment nut and adjust the slides to verify that they are all the way down. Also make sure the jets are adjusted and the throttle cable isn't hanging up.

 

[brettp]

Is your idle screw all the way up/in?

 

[Stubro]

I just finished a carb overhaul on my CB750 K1. After reinstalling, the engine fires up great but is running WIDE open. I've checked the chokes and slides for proper orientation - all good. I've checked and re-tightened the hose connections at the engine and the air box. I also, disconnected the throttle cables. The slides appear to be all the way closed. Any ideas???

Thanks,
Silvertire

How did you clean the carbs??
Did you clean the emulsion tubes?
Your idle is from a lack of fuel flow through the emulsion tubes or you have a vacuum leak through old rubber intake insulators, #7 & 8.
Aftermarket insulators are known to have leaking problems.

 

[Silvertire]

Thank you very much guys! I’ll check those things.

 

[Silvertire]

Update. Embarrassingly, it turns out that the high rev problem was due to operator error - I was unaware there was an idle screw. After I found that, the RPMs came right down, but it ran like shit and leaked a lot of gas. I pulled off the carb again and found that two of the floats had tiny punctures and were filling up with gas. Got new floats and float valves. Also, two of the float covers were leaking gas between the brass outlets and the aluminum case. Soldered those. It still runs like shit, but it's not leaking gas. This thing is the worst girlfriend I've ever had.

 

[brettp]

Update. Embarrassingly, it turns out that the high rev problem was due to operator error - I was unaware there was an idle screw. After I found that, the RPMs came right down, but it ran like shit and leaked a lot of gas. I pulled off the carb again and found that two of the floats had tiny punctures and were filling up with gas. Got new floats and float valves. Also, two of the float covers were leaking gas between the brass outlets and the aluminum case. Soldered those. It still runs like shit, but it's not leaking gas. This thing is the worst girlfriend I've ever had.

Two more things necessary. Does the bike rev all the way through the RPM range?

 

[Silvertire]

Yes. It will go all the way up to close to red. I did fool with the air screws (1 turn out) and got it running pretty good today. Still too a little rough to drop the idle down to 1k. I’m thinking about getting a carb sync kit. Would that help? Thanks!

 

[brettp]

It would definitely help.