I have a 1600 Type 1 with SVDA distributor. I set the timing to 7.5 BTDC at idle and I was wondering why you have to disconnect the vacuum pipe to set your timing when this is connected during normal running? Why not leave it connected and set it to whatever it should be?
It shouldn't make any difference at idle, but wise to check. If it does, your tickover is too high, the vac signal is too strong (ie connected to wrong part of the carb), or you have a problem with the vac can. As it advances the timing under low loads, leaving it attached to check the full advance will give a spurious result, dependent on the loading rather than the engine speed.
Thanks Zed - that makes sense. My idle tickover is too high (about 1200rpm) but my idle speed screw is in as far as it goes so I can't reduce it.
No the carb has an idle circuit which doesn't work if the throttle butterfly isn't set correctly. Lots of people use the throttle butterfly adjustment screw as the idle screw throwing the settings out, it usually means the idle wont come down with the idle screw, it's worth checking the choke is fully disengaging too
^what zed said. The vacuum advance (which is added to the mechanical advance) is really too unpredictable to use when setting the timing. So...you use the mech advance during setting (either statically or max with engine running), then just assume the vac advance is ok. You couldn't really replicate the conditions to measure it reliably.
At 1200 rpm you are running with 10 to 15 degrees of centrifugal advance. This results in needing strange settings to keep it running as it will drop to too retarded if the throttle is closed making it stop. Start with static timing to 7.5 using the voltmeter or light on the points. Made this mistake a couple of days back... in a hurry to get it running at all didnt check properly and was rewarded with wild tickover that wouldnt settle down. Set static timing, and wound down the carburettor and now it ticks over nicely.
