Topic: '72 CB750 hard start (rich?)

[KeithB]

1972 Cb750 with 557A carbs.
Valves adjusted, new coils and wires, 5k plug caps, new D8EA plugs, carbs vacuum balanced, Dyna ignition and strobe light timed (dead on)
120 mains 40 slow 26mm float,  idle screws adjusted after warm up (ended up about 1.5 turns out)
Stock airbox and filter.
Battery new and fully charged.
Turns over and stumbles quite a bit before catching and then needs some gentle throttle to get it up to a clean run.
Choke seems to make it worse and once it has run for even 30 seconds, it will start up again right away.
Pulled plugs and they seem a bit wet with gas.
I have not run this on the highway yet so cannot comment on main jetting but the transition from idle to part throttle seems good around the parking lot.
Suggestions welcomed.

[flybox1]

Get the bike hot.   Put in a new set of plugs and restart it.
Let it idle, with a fan on the front case, for 3-5 minutes.
Pull the plugs and show us what color they are.  (Your looking for a light tan insulator)

Idle screws should be set for mixture, not by idle 'sound'.
Sound is not an accurate indicator of lean/rich mixture.  Spark plug deposit color is more reliable.
 

[KeithB]

Will do.

[KeithB]

The air screws were actually at 1 turn out not 1.5 for the first test.

Plugs 1-2-4 came out a bit on the caramel side and plug 3 was a bit more sooty.
Cleaned the plugs and re-did the test with the air screws turned out 1/2 more .
1-2-4 were a bit lighter and 3 still a bit darker.

Re-checked carb balance as well.

[PeWe]

Exhaust is a rather open 4-1?   If 4-4 mains can be too large.
Ignition lined with "F" at idle, full advance around 2500-2600 rpm? Sloppy advancer springs will cause too early advance.

Floats might not work correct and cause an initial overflow. Clear tube will tell

[flybox1]

Go out/leaner on #3 screw by 1/5 turn.
The rest look good.
When cold, and as soon as it fires, you'll hear the RPM's increase while it warms up.
Start taking it off choke incrementally until it can idle on its own without choke.

Since the plugs look good, and youre assured the timing is good, it might just be the nature of the beast.
I know my F takes a bit to get going if its cold, or its been sitting.

Another cold start up procedure is to hold the throttle open, choked, and hit the starter for a few seconds with the ign in the OFF position.
Then turn the bike to RUN and start it up.

[KeithB]

I will make the #3 adjustment.
Will try the starting procedure you suggested.
While I understand it's "the nature of the beast" of the 3 CB750s and the 1  CB550/4 I have built, this is by far the hardest to start.
Thanks