Topic: CB750K1 Cold starting observations.

[pjandrew99]

Dealing with continuing cold starting issues with my CB750K1. I'm pulling the carbs off soon to clean, change slow jet (38 to 40) and bench sync along with redoing the 3000 mile maintenance. Struggling to get this bike running properly.
One thing I noticed while battling the starting issue is that to start it I need have full choke and hold the throttle open about 1/3. If I don't hold the throttle open there is zero chance of starting it. Why?
Also, if it does start, reducing the choke (move the lever down) raises the idle DRAMATICALLY.  Shouldn't it be the opposite?
Before I reinvent the wheel and start over again, hoping the above info is a clue to what may be the problem. 
Thanks

[newday777]

"Also, if it does start, reducing the choke (move the lever down) raises the idle DRAMATICALLY.  Shouldn't it be the opposite?"
The roundtop carbs(if that is what you have???)that came on the pre 1977, do not have a high idle cam on the choke, it only cuts off the air inlet flow(if your choke slides are properly adjusted???) So idle speed is not effected with choke on. All the choke does is to have a richer gas mixture. The idle speed getting higher as you remove the choke says you are running lean, from jetting or plugged idle circuits in the carbs or leaks in the carb isolator boots.

[newday777]

Have you done a compression test? What are the results from your compression tests?

[scottly]

One thing I noticed while battling the starting issue is that to start it I need have full choke and hold the throttle open about 1/3. If I don't hold the throttle open there is zero chance of starting it.

It is a normal cold starting procedure to open the throttle with the choke fully closed. Is that your only problem?
Next..

[pjandrew99]

"Also, if it does start, reducing the choke (move the lever down) raises the idle DRAMATICALLY.  Shouldn't it be the opposite?"
The roundtop carbs(if that is what you have???)that came on the pre 1977, do not have a high idle cam on the choke, it only cuts off the air inlet flow(if your choke slides are properly adjusted???) So idle speed is not effected with choke on. All the choke does is to have a richer gas mixture. The idle speed getting higher as you remove the choke says you are running lean, from jetting or plugged idle circuits in the carbs or leaks in the carb isolator boots.

Thanks, I'll check it out.

Have you done a compression test? What are the results from your compression tests?

100-100-100-120

One thing I noticed while battling the starting issue is that to start it I need have full choke and hold the throttle open about 1/3. If I don't hold the throttle open there is zero chance of starting it.

It is a normal cold starting procedure to open the throttle with the choke fully closed. Is that your only problem?
Next..

If it does start, its rough. I start to let off on the throttle while very slowly lowering the choke lever. Then the idle goes through the roof.

[scottly]

The idle goes through the roof with the choke open and the throttle closed?

[pjandrew99]

The idle goes through the roof with the choke open and the throttle closed?

As soon as I start to open the choke (move lever downward) while closing the throttle, idle jumps dramatically. Yes