Subject: Idling at 600 rpm, 1200 rpm, 1500 rpm; mine does them all, at
random
Michael wrote:
> I own a pretty much stock 1966 SPL-311 -- twin SUs, points, condensor, et
al
> -- that sits there and idles just about wherever (and whenever) it feels
> like. Most days, it maintains between 1200 and 1500 rpm at idle -- no, the
> choke's not set -- but sometimes it settles down to a polite 600 to 800
rpm.
Hi Michael,
The fact that the idle "settles down" on its own suggests an ignition
timing problem.
Often times a weak or broken centrifugal advance spring will allow the
dizzy to select random advance settings based on RPM.
Initial timing fluctuations of as little as ten degrees can cause
several hundred RPM differences which have little or nothing to do with the
carbs or air leakage.
You might want to try this test to see if the dizzy is causing your idle
fluctuation problems.
Disconnect the vacuum advance during this test (to eliminate it from the
readings.)
With suitable timing light, note the initial timing number (at the
damper pulley) and then rev the engine to 3000 RPM or so. The timing should
advance smoothly and then return quickly to the initial advance position
when the throttle is released.
IMO, the dizzy should restrict all centrifugal advance prior to 1000
RPM, but yet allow total centrifugal timing advance by no more than 2500
RPM.
If your dizzy cannot hold the centrifugal advance in check below 1000
RPM, you may want to replace the fly-weight springs and generally clean and
service the entire unit.
Kim Blough
Idaho Z Car
2913 Garrity Blvd.
Nampa, Idaho 83687-2629
1-208-466-0004
|