Re: [HSS] "Marvel"ous News, Geoff

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Tom Goodman wrote:

>

> Geoff, thanks for your help with the Marvel Carburetor beast. After

> doing all the messing around with calculations, research,

> brainstorms, fretting, stewing, taking apart and putting back

> together, I arrived at what feels like a good result. My '28 no

> longer neither belches clouds of black smoke nor does it smell like

> it is running with the choke on. What I did:

>

> (1) As you suggested, I reduced the apparent size of the intermediate

> and high speed jets by hanging pieces of wire (#30AWG x 2 in high

> speed and #30AWG x 1 in intermediate)in the hole.

>

> (2) As you suggested, I reduced the level of fuel in the float bowl.

> This I did by shimming between the cork float and the brass arm with

> some plain old paper gasket material.

>

> I no longer choke in my own fumes. Thanks

>

> Tom

>

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Tom, glad it worked for you, as it did for me. What happens is that

the float gets slightly heavier over the years with a build up of

residue, and slightly "fuel-logged". Together with the lighter

specific gravity of modern fuel the fuel level is actually above the

level of the low speed jet, hence the constant dripping that most

Marvel carbs exhibit. By lowering the fuel level and reducing the jet

size the original fuel-air ratio is restored. Of course there are other

factors to consider as well, such as flapper position and spring

tension, but all things being equal, you should get a good run out of

your modified set-up. Another thing to be aware of, if you have

trouble starting, and idling, with rough running, is the intake tube in

the hot-box. This was originally of ordinary steel tubing, and

eventually rusts through, allowing exhaust gases into the intake tube.

Easy enough to replace - remove the throttle butterfly and shaft, drive

the old tube out, and replace with either copper or stainless. You may

need to cut down the top of the old tube with a hacksaw blade to get it

out of the top part. Also, the exhaust heat is not really required

with modern fuel, so it's probably a good idea to disable this

altogether and put a stainless plate between the flanges of the by-pass

butterfly. Stops corrosion by exhaust gases, of the inside of the heat

exchanger. The flash point of modern fuel is much lower than 1929

stuff, as anyone who has experienced vapour-lock in hot weather will

attest. Have fun,

Geoff.