Greg Nagy writes:
> While on a skiing trip, the float plug on the rear carburettor of my
> 1970 Volvo developed a leak. I thought that once I got home, I could replace
> this plug with one from a Stromberg taken from a 76 Midget. However, while
> the carbs were the same, there was a totally different plug on the float
> chamber. These are CD175's. Does anyone know why while the rest of the float
> chamber appears to be the same, the one plug (from the Volvo) is a large,
> brass plug that screws around the jet, while the other is just a
> non-removeable plastic plug. Is it ok to interchange the two? There is still
> to great a chance of snow to pull out my MG and let the Volvo sit til carb
> rebuild kits come in.
Before emission controls, Stromberg carbs had an adjustable jet assembly for
setting the mixture. This was a large brass jet holder into which the jet
adjuster was screwed. This assembly screwed into threads in the carburetor
body and sealed to the hole in the float chamber cover by an O ring.
The emission control carbs had fixed jets so the jet adjuster assembly was
not needed. It was replaced by a brass plug which also threaded into the
carburetor body and sealed to the hole in the float chamber cover with an
O ring. After several years of making emission control carbs, Stromberg
started using a plastic plug which had small fingers that clipped to the
inside edge of the hole in the float chamber cover, and also used an O ring.
It sounds like the O ring sealing the plug to the float chamber cover has
gone bad. I have never tried swapping a plastic plug for a brass plug,
though it makes sense that if they are both CD-175's that the covers are
the same. Even if it fits, you may have trouble getting the O ring to seal.
An O ring that has been in service for a while tends to take a set and
harden to the shape of its confines. If removed and replaced it may not
seal properly. Have you tried calling a local auto parts store? They may
have the proper O ring. If not, you may want to chance swapping the plug
or perhaps just the O ring from the MG. You will have to remove the float
bowl from the MG's carb to remove the plug from it. If it works, you will
be all set, but if it refuses to seal because it's old, you may be in a
pickle as it will probably leak when you put it back into the MG as well.
Good luck.
Bob Leger
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