81 special ignition question

[leggman1]

I started my 81 special today and I took the left cover off to watch the vacuum can move and it didn't. It would pull if I removed the hose from the number 2 carb and sucked on the hose but not on it's own.
When should it pull? on idle or at higher rpms.
Is there a mechanical advance?
Presently I do not have any breathers/air filters on the engine at all.
Thanks. Dave

[TopCatGr58]

Hey there,

The Vac. Adv. pod only works mostly during cruising rpms, 3-5 k rmps and under low throttle input. It's not supposed to move at idle, the butterfly valve is notched and positioned to not let any vacuum signal go to the vac. adv. when it's closed/idle position.

The cent. Adv. curves are programmed electronically into the TCI(specific to the 81 4R0 series TCI's), so that's why there aren't any mechanical adv. parts. The vac. adv. is almost a misnomer, because it mostly kicks in during cruising rpm's to help adv. the timing more to help save fuel, but when you want more power and crank the throttle open more....it looses vac. and releases rotating the timing plate from the maximum of 52 degrees adv. back to ~35 degrees of adv. which is the max for the best POWER point of timing adv., so the vac. adv. actually retards timing in that situation.

T.C.

[leggman1]

Thanks for the info