Topic: 1972 CB750 Sluggish Throttle Response - Oversize slides possible?

[denward17]

From the honda service manual I found this, which appears to indicate 2500RPM you should see full advance.

Next, raise the engine speed above 2,500
rpm : if the timing index mark is between
the two timing marks located at 23.5~26.5°
ahead of the " F" mark, the timing for both
idling and full advance is satisfactory.

[PeWe]

Both my bikes with cut springs get full advance at around 2600-2700 rpm.
Just cut them...
This is a Honda design flaw as lack of frame kit.

Pull engine for open valve cover is silly!!
The oil weaping CB750 need to lift head without pulling engine too.

I had to pull my engine the first year I owned it due to ugly stock oil weap after 20.000km total since new.

[Tracksnblades1]

You could put a timing light on it and see if the timing is scattering about below 2000 rpm or especially when it dies.

Back in the late 70’s a lot of 836’s locally ran 125 main jets with bread box air filters. They were plenty fat with stock carbs and cams…

I would slowly use the choke at the point of idle instability to see if richer is better or worse..
The same can be done at 5,000 rpm but it’s not very safe if it’s waiting to climb on the pipe…

[TheWiredNinja]

The advance is pretty solid at full advance marks.  That's all I've been really able to witness since it won't dip further, but considering the shaft has been trued, I feel it won't be an issue.

New update: I cut the springs by one ring.  Installed on the bike and it runs like crap now.  I assume this is because the bike is so rich, it needs the advance to fire properly.  This also indicates that full advance has now been raised closer towards +2100 RPM ( I will have to confirm this but that's all the bike could really rev at now)

Just waiting on those jets!

[PeWe]

CB750 specified full advance is 2500rpm.
A few hundreds later - no problem.

Earlier - problem

This is what I have noticed, stock and with various cams.

[HondaMan]

CB750 specified full advance is 2500rpm.
A few hundreds later - no problem.

Earlier - problem

This is what I have noticed, stock and with various cams.

+1 on this.
Today (in the USA) the gasoline burns very slowly, by design. Slower spark advance goes with this.