Probably because that float became saturated, and now is heavier, or there
was a spec of dirt in the needle & seat. You didn't lean it out, you just
lowered the float level a little bit. The proper way to adjust the floats is
to remove the screw on the side of the bowl, and turn the nut untill gas
just starts to run out the hole. I would pull the bowl and metering block
and clean them real good, and shake the float to see if any gas has entered
it. If it has, then replace the float. Then check the float level.If you
still suspect it of running rich after properly adjusting the floats, you
need to pull a spark plug to verify it. If it is, then you will need to
change jets. If it's the secondaries that you suspect, then you need run it
wide open, or at least untill the secondaries are open for a little bit then
shut it off without lowering the rpms to get a true reading on the spark
plug. Then you would change the rear jets accordingly. If you suspect the
primaries, then you would just let it idle for a few minutes and then shut
it off, then pull a plug. You would then change the front jets accordingly.
I suggest when changing the jets to go 2 sizes at a time till you get the
desired results.

Gary

"Brad and Mia" wrote in a message:

Check the power valve. It is probably busted.

Erich
BTDT on a 83 F250

Hey guys.

This is for my 1980 351M Bronco, but I know you boys know what you're
talking about, so....

My Q is that one day my Bronc ran fine, the next day, a POS and would just
constantly stall with lots of black smoke WOT.

I went straight to the carb (4160) and checked the floats and the
secondaries were just gushing gas. My question is how? What happened that
they would do this? The lock screw was tight and the day before it ran
perfectly.

So I leaned it out big time - about a full turn on the nut - and it runs
good, but still blows a little black WOT.

Any thoughts on this... I swear, the float screws were tight. Why would it
just flood out like this???

This truck gets 10mpg on a good day. I fear I am down to 7 or 8 now until I
can get the carb set right...

Thanks all!

Brad

The suggestion about the power valve is probably good.  Also, the
needle and seat assembly has a o-ring on it.  If it is tired and worn
gas will push past it from the fuel inlet directly into the bowl
causing flooding.  (The needle and seat assembly is actually what you
are raising/lowering when you turn the adjusting nut.) Holley's
rebuild kit is only about $25, includes new needle and seat assembly,
gaskets, power valve, accelerator pump diaphragm, check balls, etc. No
jets, though.

If the old gaskets stick when you disassemble the carb, 95% rubbling
alcohol will soften them up for easier scraping.

Gary H
66 GT