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CARBURETORS
Frank Hofmann Technical Counsellor #3013

What do I know about them?

They leak.
They are awkward to attach and to detach.
There are few competent shops around who appear to know what they are doing.
They are expensive to repair and even worse, to buy new.

I had a problem with my 1938 vintage Stromberg NA-S3A1 carb. I removed it and tried to get informed. Various phone calls resulted in much insight.

Parts are no longer available. People are selling "Delrin" needle valves instead of neoprene or steel ones. But the problem apparently is not with the materials but rather with the radius of the needle seat. Only one old gentleman in the States appears to know what that radius should actually be. He and his wife claim to be turning out Stromberg carbs which on the whole don't leak - much.

The obvious action, sending it to an "Approved" shop cost about $200 and left the carb still leaking. Off it came again.

A variety of telephone calls to the technical experts of a number of "Type" clubs resulted in statements such as: "They all leak - just shut off the fuel when you park." Another comment was: "Yeah, they have leaked since 1938."

The trouble with all that is that the log books for my airplane show a fire and a subsequent engine change. I don't want to see that again.

$1100 will get you a rebuilt replacement carb from Precision Airmotive for a C-85 Continental, if they happen to have one in stock - relative rarity. ($1700 US new!) I bought the only one in the USA at the time.

So now it is mounted on the engine and is working great. A new piece for which replacement parts (and eventual AD's I'm sure) are finally available.

But in the process the folks at Precision were good enough to attach some information regarding carbs which I found very instructive. I've spent my life thinking an MA-3SPA is an MA-3SPA, different from an MA-4SPA to be sure, but the same as any other MA-3SPA which you see advertised. Was I wrong! Have a look at the attached list. I don't know how the passages drilled into the body of the carb vary from one model number to the other, but there clearly are differences.

The moral? To own, operate and maintain an airplane takes much knowledge, and even more money.

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Frank Hofmann
Copyright © 1999