On Sun, 6 Jan 2002, Scott Allen wrote:
> The rear carb has a small brass pin in the base of the piston so that
> when the carb is assembled it holds the piston a few thous' off of the
> bottom of the chamber. It appears to be spring loaded so that if you
> press down on the piston it will go flat against the bottom of the
> chamber, but when released it pops back up and there's some clearance.
Some SU pistons have that spring-loaded pin, some don't. It's purpose is
to soften the blow of the piston on the jet bridge, but I've never
understood why it was thought to be necessary. The piston almost never
hits the bridge when the engine is running anyway. The fact that one of
your pistons has it and the other doesn't means one is a replacement.
Other than that it shouldn't matter as long as both pistons weigh the
same, have the same strength piston springs, and the same pattern dampers.
--
Chip Old 1948 M.G. TC TC6710 XPAG7430 NEMGTR #2271
Cub Hill, Maryland 1962 Triumph TR4 CT3154LO CT3479E
fold@bcpl.net
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