Float adjustment - older carburetors

[carbking]

A tip for adjusting floats on older carburetors:

The maximum force exerted by the float on the fuel valve plunger will always be when the portion of the float contacting the fuel valve plunger is at a 90 degree angle (right angle) to the fuel valve plunger when the valve is closed. If the portion contacting the valve plunger is not at the 90 degree angle, some of the available force will be pushing sideways on the valve, and the valve may receive insufficient vertical force to properly close.

When the carbs were new, the common accepted practice was to bend the float arm (or float tab, if the float arm had a tab) to acquire the proper adjustment.

Today, depending on the design of the carburetor, a better method may be to change the thickness of the gasket sealing the fuel valve seat to the carburetor. The reason for this change is that the float arms are generally made from brass, which becomes more brittle with age. Bending the float arm or the tab may result in OOPS!!!!! now where can I find a new float???

Often these older floats are made from unobtainium, or at the least, verypricium.

Thinking outside the box with the adjustment can sometimes save one a significant headache, or a hole in the wallet.

Jon.

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[keiser31]

Thank you for that. Very informative.

[NTX5467]

Some good thoughts and comments, carbking!

In some respects, it seems that adjusting the float with a carb overhaul/rebuild can be overstated. Reason is that even with a new needle and seat pair, it seems the float level was still "in specs" with the new parts (which looked just like the "old parts", except for the "contact ring" on the needle's rubber contact cone).

In more recent times, the externally-adjustable floats on Holley 4150-style 4bbls (and similar 2bbls) makes things somewhat easier to do . . . then as now.

In many respects, when you invert the float bowl with the float and needle/seat installed, the right angle (mentioned) between the fuel line on the float and the gasket surfave of the float bowl (usually horizontal, in many cases) results in the "right angle" carbking mentioned. You can eyeball this without any of the "fancy" stepped measuring gauges in the carb kits, too.

Thanks for the tip!

NTX5467

[TexRiv_63]

A tip for adjusting floats on older carburetors:

When the carbs were new, the common accepted practice was to bend the float arm (or float tab, if the float arm had a tab) to acquire the proper adjustment.

Today, depending on the design of the carburetor, a better method may be to change the thickness of the gasket sealing the fuel valve seat to the carburetor. The reason for this change is that the float arms are generally made from brass, which becomes more brittle with age. Bending the float arm or the tab may result in OOPS!!!!! now where can I find a new float???

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Not sure if this is a trend but I just rebuilt the 4GC on my Olds and the kit included multiple thickness gaskets for the valve seats and instructions to do exactly what you describe.

[hchris]

Not sure if this is a trend but I just rebuilt the 4GC on my Olds and the kit included multiple thickness gaskets for the valve seats and instructions to do exactly what you describe.

Ditto Texriv, found the same multiple choice gaskets with some Zenith kits recently purchased, why didnt we think of this before??.

For the rest of those float settings, as Carbking says, bending brass tabs is fraught with danger.

[carbking]

Actually, the reason one finds multiple gaskets in some of the commercial rebuilding kits, is kinda, sorta, almost related.

Many of the commercial rebuilding kits are a classic example of "one size fits all" (or doesn't fit any). Carter produced more than 100 different fuel valves for use in the AFB carburetor (different orifice size, different height, different configurations). These are replaced in the commercial kits by one valve. The various gaskets are there to at least compensate for the difference in height. Guess what happens if you put one of the replacement valves measuring 0.101 in a carburetor originally designed for a valve with an opening of 0.086.

Jon.

[NTX5467]

Sounds kind of like the "will fit" egr valves where the "replacement" valve needs to have a washer inserted in it for the particular engine size it's being installed in, rather than an "application-specific" OEM replacement part.

Take care,

NTX5467