I've got a head scratcher going on here:
In preparation for an engine swap, I put my newly rebuilt HS2 carbs on
the old engine (948 set up for HS2's) to tune them in and make sure they
would run when the time came to install the new engine (1275+). The
install went well, and once the float bowls filled with gas the engine
fired and took right off, with no additional adjustments needed for
balancing the two carbs. However, the engine idles at about 1500-1800
rpm. I've checked that the cables are set right, the throttle plates
(butterfly) are closed at idle, the choke is disengaged, and the high
idle set screws are completely slack.
When I rebuilt the carbs, I did not replace the needles, as they seemed
to be in good shape with no obvious wear. The needles are correctly
centered in the jet, and the piston slides well and hits the bridge with
the prerequisite "thunk" of a properly functioning piston. The only
think I can think of that might be causing this is that the throttle
plates are the style that have the spring loaded button valves in them.
I did not use the blank throttle plates that came with the rebuild kit,
but still have them. I took the car out for a drive and there was a
noticeable improvement in "get-up-and-go" with the new set, throughout
the rev range. It's just when I came back and parked it, the idle would
sit steady at 1500-1800 rpm.
I have the Brooklands SU Carburetor manual, a Haynes manual, and Ball's
Spridget manual. None of them have any troubleshooting clues for a an
excessively fast idle. Any help from the list would be appreciated.
Tim C.
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