I am trying to get my distributor set at it's best point. It is one of the Datrats bluebird series 2 modified items that has both mechanical and vacuum advance functions. I set the ignition timing at idle of 800rpm with the vacuum advance hose disconneted and plugged at 5 degrees but when I connected the hose again the idle goes up to 1000rpm and the ignition advances to 10 degrees.
I am considering leaving the hose disconected and the idle set at 800rpm and 5 degrees since the mechanical advance would probably be enough to advance the timing when the motor revs increase
Has anybody else had this issue before or something similar, I just want to get the lowest idle and correct ignition timing

That sounds pretty normal.....

remember that vacuum advance only works when the throttle closes, or are partly closed.... IE under partial engine load....

this will advance the timing and give much smoother operation... than when you floor it, the timing will retard for full load operation.....then only the mechanical advance has an effect on the timing, so as the revs go up so will timing be added.

Sounds like you are connecting it to manifold vacuum & not ported vacuum. On the other hand, if it really is connected to the right fitting on the carb, then it would seem that the throttle plate is open far enough for the vacuum port to see manifold vacuum & start sucking in some advance, even at idle.

See if you can use a vacuum guage to help tune the carb & stabilise the idle. The higher the vacuum at a given engine speed, the better, as this indicates a 'best mixture' condition. I use a big old Redex tune up one from the 60's about 100mm [4"] in diameter. It sure helps my tune ups.

yep it's definately connected to the ported vacuum nozzle on the carb just above the butterflies, I will try closing the butterflies a bit at a time with the idle speed screw and checking to see what afect it has on the vacuum reaching the dizzy diaphram by checking the ignition timing, mayby I will need to set the idle to reach 5 degrees ignition timing then re-set the lean best idle on the carb to suit?

excuse me for asking a question in some1 elses thread.

but do you even need to hook the vaccum advance up?

i have one of these dizzys on an A15 with twin 40DCOEs - as Zane knows - and was thinking that i wouldn't worry about the vaccum advance. good idea or not?

can some1 tell me exactly when the vaccum advance comes on (part, full or closed throttle) etc.

why do you set the idle speed without it on?

my understanding with this dizzy used on twin sidedraught systems is not to worry about vacuum advance and to set the base ignition timing at between 10-14 degrees. I don't think sidedraughts have ported vacuum advance outlets mainly because they don't generate enough vacuum with 4 throttles.
I think R-Fastmotorsport uses that set up on his engine
Thats why I was wondering if I should try it without vacuum advance hooked up, but I will give it some more attention before I give up