Guys... I can't set the rear float on my Holley 4160 (351M).
The float nut will loosen, but not tigthen unless it moves the screw with
That is, I can't set the screw to where I want it, and hold it with a
screwdriver and tighten the nut... the nut just spins. Unless I remove the
screw driver and let the screw spin with the nut to tigthen. Does that make
What is this and how can I fix it?
Also, turning the idle misture screws in leans it out? Correct? Loosening
them makes it more rich?
The "nut" is what adjusts the height of the needle and seat.... the screw is
what locks everthing in place. It almost sounds like your needle and seat is
screwed to far in.... don't forget that the fuel level in the secondary
float bowl will not drop until the secondary throttle plates are opened and
fuel flows through the carb circuits.
If the fuel level is higher than the sight plug the fuel level (as well as
the float level) will both need to be dropped. Opening the secondaries in a
driving situation, will lower the fuel level. Once the fuel level is
reduced, we can "sneak" up on the adjustment.
I suppose we could fart around for a while and let gas drool all over the
manifold but I think my way is more fun.if a safe acceleration lane is
Ah, so you're saying you have to gun the throttle. That will move the
secondary float. So when you let off the throttle then, the float will stay
where it is and you can see if it needs to go up or down? Kewl.
Thanks again guys.
You can "fart around for a while and let gas drool all over the manifold" if
you want but I usually only spend a few minutes adjusting the float level
and maybe spill a small amount of fuel onto the rag I've placed under the
float bowl. Of coarse I still have to test the secondarys in an appropriate
place. Best of both worlds, the job is done quickly and I still get to have
I think Bob thought you were talking about the idle mixture screw, (usually
needle-shaped), as that was one of your other questions.
The inlet valve assembly should just unscrew out the top.
Try not to lose the little gaskets between the screw/nut and nut/housing, and be
careful of the O-ring on the outside of the valve body. Try not to chew it up on
threads as you pull the valve out.
Some carbs have a sight "glass" built into the side of the bowl, so you can
level without opening anything up. There's usually a line of some kind on the
Others have a sight "plug", where you take out the plug, and adjust the level so
at the bottom of the hole, not quite high enough to dribble out.
Other don't have anything, and you get to set the level manually using a
with the float bowl sitting on the table in front of you.
Different year / car / trans / engine / whatever = different setting.
Almost forgot something "slightly" important... if you do try to just unscrew
the valve body without taking the float bowl off, there won't be anything left
inside holding the inlet valve needle (also needle-shaped) in place, it will
into the float bowl, and you'll have to take the whole thing apart anyway.
The inlet valve is threaded into the float chamber body, with the top of the
threaded area filed flat on two sides. The unthreaded "nut" just acts like a
wrench on the flats, allowing you to raise/lower the fuel by screwing/unscrewing
the entire inlet valve. The screw on top just clamps the whole mess together so
it can't spin.
Depends on the exact model you have.
Some versions of 4150/60 have a "reverse" adjustment; in-rich, out-lean.
They usually have a sticker by the screw that says so.
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