Tuesday, June 10, 2008

Do Duel Carbs Make My Butt Look Big?

Dad just posed the following question:

I'm wondering if your carbs were re-jetted for our altitude after moving
from Chicago.

The way the Amal's are designed, fuel flow is proportional to the throttle
opening. Fuel pulled in at the venturi is somewhat dependent on air flow
but not to the extent of SU's. With SU's, piston height is proportional
to air flow, and they would better compensate for differences in air

With the Amal's, lower air pressure could mean a richer mixture. Air
pressure in abq is about 80% of sealevel pressure.

Good question.

Aubrey mentioned that he had spoken to Southwest Cycles about proper jetting when he moved. They recommended he drop the needle to the lowest setting (highest notch), which would make it leaner. Based on the carb book Rob sent me, if the main jet was too large it would mainly be noticeable at 3/4 to full throttle. Theoretically the needle adjustment would counter act that setting to some degree in the mid throttle range. It seems bad through the whole throttle on the RH side. Full throttle is the only time the RH seems to clear out at all.

I called SW Cycles now and they said they normally start out in the 170-190 mainjet range. I can't remember now what size I'm running. They did offer the same needle advice if it was in that range. They also suggested bumping the timing 5 degrees to adjust for altitude.

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