Topic: Carb syncing - one carb doesn't register - CB750 K1

[mycb750k6]

I just tried syncing my carbs with my carbtune. Number three carb will not register on the display at all but the bike seems to run OK. I tried blowing out that connection hole but nothing. Switching hoses confirms it's the carb and not the carbtune which I just used the other day to sync a friends carbs without issue. What would keep that carb from sucking like the others?

[jessezm]

My friend had the exact same problem when he borrowed my carbtune to sync up his 350f.  He thought he had broken it, but it worked just fine the next week when I did my bike.  My hypothesis was that the tube was kinked or pinched, but your experience doesn't bare that out.  Maybe start with that carb first and adjust it until you get some kind of response, and then adjust the others to that one?  I really don't know what else it could be.  Does the pipe warm up with the rest of them at idle?

[KingCustomCycles.com]

Failed intake valve will blow rather than suck, which blows.

[phil71]

valves too tight will also make a cylinder into dead spinning weight..

[mycb750k6]

What's odd is the engine runs strong through the gears. Wouldn't run like that on three cylinders or valve leakage problem me thinks. I re-seated the valves and set the tappets when the valve cover was off so I'm gonna pull the carbs are try some others.

[KingCustomCycles.com]

pulls good with a bad valve, pulls great with a good valve.

[mycb750k6]

How does one define a 'bad valve' in this situation?

[KingCustomCycles.com]

Leaking for whatever reason.  Carbon on seat, pitted seat, bent or warped face, burnt face, misaligned seat or guide, being held open by rocker arm, weak or broken spring.