1975 Honda CB750 - too rich?

I've been troubleshooting the carburator on my bike and seem to be
making progress... although it's hard for me to know as I'm a complete
beginner here.

I adjusted float height today and had some problems at start up (the
engine wants to quit and I have to compensate with more gas)... I
figure too much or not enough gas in the carburator.
However, once it's running then it seems fine.
Two things I noticed: when I forgot to shut off the gas tank valve,
there was small fuel leak stain when I returned later.
the second, is that when I down shift to first, and at other times in
first gear, I hear what I'd describe as loud gurgles or
"mini-feedbacks" coming from the muffler.

Here's my questions:
Does this point to too rich a fuel/air mixture?
Is there any way to adjust air intake or ratio into carb, or is fuel
the only thing that can be adjusted?
If it's just a matter of bringing down the floats, what is the
appropriate measurement, or is it just gradual adjusting until it feels
right?

thank you so much in advance for your time and expertise.

 

Re-adjust it correctly, after making sure the float and needle are good.
Change your oil to get rid of the fuel in it due to the flooding.

 

I suggest you have another look under the tank. There are three more
carbs there.....

 

It's quite common to hear such strange noises coming from the exhaust
system.

The engineers at Honda simplified the ignition system by using two dual
lead ignition coils so they would only need two sets of ignition points
instead of four sets.

This arrangement means that you get one spark to the cylinder that
needs a spark, i.e., the piston is coming up on compression, but you
also get a second spark, which is called the "wasted spark". It fires
on the cylinder that is coming up on the exhaust stroke. This spark
occurs while that cylinder's exhaust valve is open.

If the fuel air mixture is too rich, you will have unburned fuel in the
exhaust pipe, and you will hear low-pitched bangs and rumblings in the
muffler as you roll off the throttle.

OTOH, if your fuel/air mixture is too lean, you will hear a "piffle
piffle SNAP!" sound in the exhaust, or even a rather loud "fart BANG!"
when you roll off the gas.

The exhaust sytem would have been a lot quieter if Honda had used four
sets of points and four individual ignition coils.

Rumbles and booms mean the mixture is too rich, snaps and bangs point
to a lean mixture.

The older style slide valve carburetors used on early Japanese
motorcycles have an idle AIR screw on the side of the carburetor. The
screw adjusts idle AIR *before* it mixes with the idle gasoline, so
turning that screw clockwise reduces air flow and richens the mixture.

The idle AIR screw will be on the side of each carburetor. About 1.24
turns out from closed is a good starting point.

If other responders start telling you that you need to "re-jet" your
carburetors, ignore that stupid advice unless you have good reason to
believe that some shade tree mechanic has actually changed the jets.

There is a cesspool of bogus information about selecting jets and
moving jet needle clips up and down and shade tree tuners will usually
install a jet that is many, many sizes too large and wind up with an
engine that puffs out black smoke.

Check www.partsfish.com or www.bikebandit.com to learn what the
original jet sizes were, and stick to those sizes unless you have an
aftermarket exhaust and are using separate air filters instead of the
original airbox.

And leave the jet needle clip in the slot it was in when it came from
the factory. Shade tree tuners have no idea what they are doing when
they move the clip to a lower slot. This does NOT affect the idle or
transition mixture at all.

It would be easy for me to say that you shouldn't be messing with stuff
you don't understand, if you don't have a manual, but trial and error
is how I learned about carburetors, and there is more information
becoming available all the time.

I don't happen to have the exact measurement for the floats handy, but
it's a critical measurement, of plus or minus only ONE millimeter.You
will have to google for the float height, or acquire a manual.

Suppose the manual says the correct setting is 14 millimeters, plus or
minus 1 millimeter. That would be a range of 13 to 15 millimeters.

Since the float level is adjusted with the carbs upside down on the
bench,
15 millimeters from the bottom of the float to the carburetor gasket
surface is a LOWER fuel level, and 13 millimeters is a HIGHER fuel
level.

If the fuel level is adjusted over a millimeter too high, this makes
it easier for the engine vacuum to suck gasoline out of the float bowl.
The engine runs "soggy", it gargles on too much fuel at idle.

If the fuel level is adjusted over a millimeter too low, it's harder
for engine vacuum to pull fuel out of the float bowl, so the engine
tends to surge and has an unstable idle RPM.
..