Hanging Idle

[GC_Toronto]

Newbie question: I'm trying to troubleshoot a racing engine on my barn find 1980 CB750C with 21K. Carbs completely redone including full tear-down, ultrasonic, fuel rod o-rings and throttle shaft seals replaced, plus new intake boots and plugs. No vacuum leaks. Starts instantly and runs fine from cold but begins to race once warm and throttled above 3K. Just wants to stay up there and has to be 'braked down' to a near-stall to return to idle. I'm thinking it's running too rich because at idle it likes a touch of choke to run smooth. In addition to your suggestions... ...does anyone have the Pilot Screw Adjustment Specs of VB42D carbs? Both the Clymer and Honda Service Manuals list details for VBA @ 1.5 turns and VBC @ 1.75 turns. I appreciate that I could start at 1.5 and work up .25 at a time but I thought I'd ask you CB gurus for your sage input.

 

[Rampton]

Mine all set at 1 3/4 turns out. Hope this helps. Regarding running rich or not pull the plugs and see what colour they are. Regarding throttle hanging but then dropping slowly I found that that was a vacuum leak, all the best, Rampton

 

[BAHNST]

Late here might be solved already...
But hanging idle as per Rampton is often a vac. leak...assuming cables arent kinked and smooth in operation.....

 

[BAHNST]

If the "hanging" idle issue is still there, here is a good resource specific to the CBX, but probably relevant to the DOHC 4s.
Consider the "header/topic" at the left of page...NOT the CBX fix
https://www.motorcycleproject.com/text/hanging_idle_cbx.html

 

[Rampton]

Very good reading BAHNST worth saving

 

[barrett_patton]

I have a similar issue- did you ever resolve this? What did you find out?