[TR] TR3 fuel pump

Randall tr3driver at ca.rr.com
Fri Feb 27 20:29:01 MST 2009


> I find that it only pumps when it is able to move fuel.  When 
> the  floats are full and the float valves are closed it not 
> no longer pumps, i.e. you  can no longer feel resistance at 
> the lever.  

That is exactly right.  In addition, if the camshaft happens to be turned so
it presses on the internal lever, the range of resistance will be much
smaller.

Both the priming lever and the camshaft lever pull the diaphragm down
against a spring, pulling fuel into the pump.  When the force is released,
the spring pushes the diaphragm up, pushing fuel out to the carbs.  The
spring tension is what limits the output pressure of the pump; so when the
output limit is reached, the diaphragm simply doesn't rise against the
pressure, and stays fully down.  That leaves the levers with nothing to do.

Randall


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