The Stovebolt Site Forums The Shop Area Engine Shop Importance of Float Adjustment?

If the float in a carburetor weren’t adjusted correctly, would it affect the way the truck runs at idle?

I dont know about all carbs but on my Demon it sure did. If the fuel level is more than about 1/4 from the bottom of the siight glass it runs way too rich.

Yep, it sure will. Improper adjustment of the float can cause flooding,starvation,or hesetation and surging.

Sure id does. Fuel level affects the whole range.
The higher the richer it will run.

@stea what Demon you got on what engine?
I`m in the process to bolt an 525 Road Demon on my 261.

Any experience? Milage? Power?

Frank

f.booth I can't help you out but I was wondering about this same question.
I have a '49 Carter w-1 684s. Using the manual I adjusted mine to 1/2" at the high position and 1" at the low position. Would this be correct for this particular model. I'm still getting a little flooding.

Frank,

Good question. I just waded through the Rochester B book, and my unprofessional opinion is that it won't affect the idle of the engine.

This assumes we are talking about a slightly out of adjustment float. On the model B, It looks like the system takes fuel from the bottom of the bowl, through a jet for final mixing for the idle circuit.

My bet is that 'carbking' will see this post and blow me right smack dab out of the water....we shall see. I have my life vest on!

Stuart

atomarc, you are correct in you finding , if as you say it is a little out of adjustment. But there is also a float drop setting that can cause a no fuel problem.

Stovbold, I have the 625 road deamon on my 350. Its a good carb but seems really touchy. milage HAHAHAHAHHA. power is good but I do think its a little fat for my motor. I was going to pull it apart and rejet it over the winter butI may shift gears and go with a 3x2 set up.

OK Stuart - I get to be the bad guy.

Float adjustment in any carburetor is critical. And this is one of the tuning "tools" that a professional may use to see what may result from changing a jet without actually changing the jet.

A carburetor provides fuel based on negative pressure. For a better understanding, read some of the better carb design books; but in a nutshell:

Air passes over a "pickup point" somewhere in the venturi area. The air will have a certain velocity or speed. This air may be accelerated by "booster" venturi or not depending on the design. The air passing over the pickup point causes a negative pressure at the pickup point. The velocity of the air will change the negative pressure, thus why choosing a correctly sized carb (if not original) is important.

The air above the fuel in the bowl is open to atmospheric pressure (through the bowl vent). In about 5th grade science we all learned that we do not suck tea from a straw, but that we create a negative pressure in the straw and atmospheric pressure above the tea in the glass pushes the tea into our mouth. A carburetor works the same way. "Bleedover" or that point at which the pressure in the bowl conteracts the negative pressure and fuel begins to flow is effected by the fuel level. The fuel lever, of course, is effected by the float setting.

Typically, 1/16th of an inch fuel level change will effect 1 jet size change in the metering.

Other issues that may effect fuel level are fuel pump pressure and fuel inlet orifice.

Float drop is less critical, but should still be adjusted. Generally float drop should be set such that the float may not quite touch the floor of the bowl if the bowl is dry.

On older carburetors (those with floats made from unobtainium or veryexpensivium) we suggest adjusting the fuel level by changing the thickness of the gasket below the fuel valve seat, rather than bending the float.

Obviously, the engine will run on less or more than the perfect mixture. Float setting has less bearing on power than on fuel economy, and driveability.

Jon.