Motorcycle Repair: Idle-750A, ebay auctions, vacuum line

Question
My 1976 750A has 7500 easy miles. It recently started running at very high rpm when the throttle is at idle. This happens after being ridden for a while,

I'm told the bike has a built in adjustment that adjusts idle rpm up when put in gear and that it may not be doing its job. any help would be appreciated.

Answer
I found a few references to CB750As on the SOHC website...

http://www.greenspun.com/bboard/q-and-a-one-category.tcl?topic=SOHC%2F4%20Techni...

This one mentions various idle speed settings for these carbs.

http://www.greenspun.com/bboard/q-and-a-fetch-msg.tcl?msg_id=00BbiG

I never worked on one of these and have no literature on them in my library. Honda still sells shop manuals for the bikes at www.helminc.com or sometimes you can get them from Ebay auctions or place wanted ads in the www.vjmc.org
or check with www.motorcyclememories.com

From the above link, it sounds like there is a vacuum line going to the idle speed solenoid. Check for a bad diaphragm, which would cause an air leak thus raising the idle speed.

I went to http://www.powersportspro.com/ log into their system and and found a microfiche listing for this bike and there is an electrical solenoid, which activates a vacuum diaphragm to control the idle speed. There is also a check valve in the circuit, too.

That's about all I have for you on this issue...  

Bill Silver