Topic: 1970 CB750 KO High Idle

[JohnK3]

My 1970 CB750 KO with about 14,500 miles has been running well. It's the model with an individual cable to each carb. A little hard to start, but when warm idled nicely and pulled strongly.  On my last ride, it suddenly started to idle at 3,000 RPM. It still pulled strongly, just idled high. 
Any idea what could have caused such an abrupt change?

[TwoTired]

Carb imbalance.  Or cable wear.  Or, needs cable lube.


Cheers,

[BenelliSEI]

Pop the rubber ends off the cables, where they enter the carb tops. Occasionally, one cable will pop out of the socket (the metal cable ends jumps out of the adjustable socket on one of the carbs). Even one held open will get the idle up there!

[BenelliSEI]

Next.... try wiggling the carbs in the intake manifold rubbers. If the idle changes make sure all the clamps are tight. Any cracks in the rubbers?

Also..... a sticking advancer (slow to mechanically retract to idle speed advance)will also hang the idle.

P.S. nice bike!

[2wheels]

Be sure to check all 4 spark plugs, looking for the (way to) white one.
Meaning you have an air leak.  Not as likely as a stuck throttle cable but deadly to the motor if it is.  So worth checking first.

[JohnK3]

Update:
I removed the fuel tank and wiggled the throttle cables to seat them in the carbs, and now it idles fine. It's possible one was off it's seat and causing the high idle.

Thanks Benelli.

[MauiK3]

That is one great photo!

[BenelliSEI]

Update:
I removed the fuel tank and wiggled the throttle cables to seat them in the carbs, and now it idles fine. It's possible one was off it's seat and causing the high idle.

Thanks Benelli.

John...... Excellent! Easy fix is always the best. If that outer cable seems a bit loose in the socket, loosen the jam nut and unscrew it a bit, so it won’t happen again.

[BenelliSEI]

That is one great photo!

Taken by a professional photographer, with a real camera. Amazing detail. He did my F and the Benelli too.