Spica engine in carburated car

[JHertzman@domain.elided]

In AD7-1193 Thomas Moll did a thorough job of covering the throttle-linkage 
end of Scott Fisher's Junior w/carbs-to-1750 w/Spica conversion, and Simon 
Favre had covered the clutch-and-pedals end, but neither (nor Scott) 
mentioned the gas tank.

The conversion from a 1300 (or 1600) Junior engine to a carbureted 1750 
should indeed be a bolt-in switch as APE and others had said, but there is 
more to the fuel systems than the carbs vs. injection pump. The carbureted 
engines have a simple one-way fuel feed, from a single outlet on the tank to 
a small filter in the engine bay to the mechanical fuel pump to the carbs. 
The injected engines have a recirculating system, with a return inlet on the 
tank, the electric fuel pump (preferably Bosch), with its filter and a very 
different main filter, as well as a fuel vapor recovery system in the trunk. 
Instead of one pipe from tank there are three. None of this is 
insurmountable, but a preview will avoid several oops. If Scott can view the 
fuel tank and fuel piping pages in a 1750 parts book (figures 12 and 13) 
along with the analogous sections in the 1750 U.S. version parts book (figure 
12, fuel tank; 12/1, fuel evaporation bellows and vent pipes; 12/2, 
vapor/liquid separator and pipes; 13 and 13/1, fuel piping; 14, fuel pump; 
15, main fuel filter; and 15/1, tank fuel filter) and then compare a US 1750 
with his Junior, he should be able to figure his needs and anticipate details 
like making the bracket for the main fuel filter.

There may be "work-arounds" which would allow a simpler conversion, perhaps 
eliminating the vapor recovery system, but the Spica pump does depend on the 
high-volume fuel flow for cooling. Perhaps the existing fuel tank could be 
used if one arranged the fuel return via a modified sending unit. I would, 
however, recommend looking at the parts books and the cars as an aid to 
planning ahead. (Or, one could chicken out and run carbs - - )

John H.
Raleigh, N.C.

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