I've been having problems with my front SU HS6 for some time now dribbling
at high rpms. I have tried a number of different float valves, both
Grose Jet and neoprene OEM valves, and the back carb is fine. I suspected
pressure problems but when I checked the fuel pressure it was rock steady
at 3 psi, which is exactly what it is supposed to be. At speeds below
3000 rpm I don't get any leakage but I DO when I wind it up and I have not
been able to rectify the problem with the current carb, which I rebushed
around Christmas 1999. Got about 3000 miles on it now.


Since the fuel pressure is controlled by the spring that backs up the
diaphragm, I don't think a stroke increase could change the pressure but it
does put more stress on the pump and make the cam push the lever at the wrong
place so I would NOT operate without the spacer.

(In a diaphragm fuel pump the lever actuates the suction stroke and the
spring pushes the fuel out on the discharge stroke. So the spring is the
sole mediator of output pressure. It may be possible for the spring to
become unseated with an excessive stroke and thus be effectively operating
in a shorter position in which case it might put up higher pressure but I
think this is pretty unlikely.)

--
George Downs, The "original" Walrus3, Bartlesville, Oklahoma