Topic: 1980 cb750 Custom ideal problems...?

[jason teamshralp]

I have a friend looking at getting a bike. His cousin has a '80 cb750 Custom that isn't running, he says it won't ideal right. Is there anything that was a problem with these bikes? I read that there is a issue with the carb diaphram but im not really sure what that is and what it does. The only bike if have experience with is my '78 cb550k. Any help, tips, or advice would be nice.

-Jason

[Jay B]

This should be in Other Bikes. Having said that, I've been dealing with my brothers '79 750 lately. Here are some things to check.
-These are VERY sensative to vacuum leaks.
-Carb slides are piston operated, no diaphrams. They must move very freely.
-There are 3 jets in these carbs, one is non removable under a rubber plug in the bowls. Make sure they are all clean.
-There are air cutoff diaphrams under a small cover on the left side of each carb. These are a constant source of headache on these things.
-Valve adjustment is critical, and most often overlooked. Tight valves will affect the draw of the cylinders and throw the carbs into fits.
-Even though these have electronic ignitions, there is still a mechanical advancer under the LEFT sidecover of the motor. Make sure it is free.

Check out my thread "DOHC 750 help needed" in Other Bikes for more.