When timing GQ TB42, vacuum on, or vacuum off

[HOTLEAD]

My Gregorys manual says when setting the timing on my GQ (points system) that I should leave the vacuum hose connected to the advance unit on the distributor. This is normally what I do and move the distributor while the engine is running while checking with the timing light. When it's right I lock up the bolt on the dissy and recheck. Just for interest, today (after setting the timing as above) I disconnected the hose on the advance unit and rechecked the timing. I found there is about 8 degrees difference when at idle.

So my question is should I set the timing (at idle) while the advance is connected or disconnected? Advice appreciated.

Jim.

[90Mav]

if the vacume advance is affecting timing at idle, the idle speed will be critical and variable when timing. if timing with VA connected, make sure idle speed is exactly as specified after each adjustment...
u will probably need a low range tachometer for accurate timing.

[skippy's GQ]

vacume line off, and pluged, then do timming and idle adjustment,, reconect vacume line... all done

[PGS 4WD]

On a GQ it shouldn't matter as the vacuum advance port is slightly above the butterfly blade, if the idle speed is correct with no other issues (like super out of tune meaning the blade is open excessivly in order to maintain the correct idle speed). Then there will be no vacuum on the advance port, it only applies vacuum at light throttle(not idle). Speaking generally if the vacuum canister has two hoses (advance/retard) then the timing is set with the lines off and blocked, such as N12 Pulsar.
The std setting is 10 degrees BTDC, set your dwell first if you still have points.

Joel