> When I get the mixture set using the lift the piston technique, I
> cannot get the car to idle at less 1000 rpm, even though I have the
> idle screw and the choke screw backed all the way out. If I richen
> the carbs up by 4-5 flats I can get it to idle the proper 600 rpm.
>
> Suggestions?
Check the accuracy of your tach. Many of them read high at idle.
Check for wear in the throttle shaft bushings. If they are badly worn, the
shaft can move enough to cause the throttle plate(s) to drag on the bore and
so hold the throttle open slightly.
Poor throttle plate centering can cause the same thing. If you pull the
carbs to check the centering, look through the carb at a light (with the
piston held up or removed) to see where the throttle plates don't meet the
bore. It's OK if there are some wisps of light near the shaft, but the
edges away from the shaft should seal perfectly. If not, you may need new
throttle plates or the ones you have may be installed backwards.
You didn't mention synchronization ... what happens if you loosen the
coupling between the carbs ? Loosen the front coupling to the linkage too,
to be sure it's not a pedal problem holding the throttles open.
Where do you have the timing set ? Fast timing can cause high idle.
Just to be sure, disconnect the line from the vacuum advance. It should
make no difference at all to idle speed.
Check all around for vacuum leaks, especially along the bottom edge of the
intake manifold (where it's almost impossible to get to). Spraying carb
cleaner at suspected leak sites with the engine running is one way to do
this ... the engine note will change if you find a leak.
And if all else fails, it's not so bad to have it idle at 1000 rpm. Much
better than screwing up the mixture that bad.
Randall
|