was wondering if the fast advance kits or springs are worth it in my 4x4 i mainly run down low and don't go over 4000 rpm

that curve needs to be slowed down. What springs are in there now?

not shure what springs. its all stock 76 440 rv motor.the can is stamped 9l the weights are L13. to slow it down could i lighten the weights or use tighter springs? thanx for the help.

tighter springs but 1st did you find out what your total is(vac adv plugged) & revved till it wont advance any higher & see what you have at that point(want 36-38 for a BB) & see what your initial is at idle(also with the vac adv plugged for this even if you are on ported vac). We need to get a baseline before we alter anything

the problem with running manifold vacuum to the advance is that if you have a hefty cam, there is usually a large difference in vacuum between nuetral and drive. and that changes the advance in the distributor which will change the idle A LOT when you drop it in gear.

With a stockish cam, you have 14 or more inches of vacuum in neutral which will bump the vacuum advance up all the way. when you you drop it in gear, you may drop manifold vacuum to 12 or 13 or more so you are still maxed out on the vacuum advance. so no change in idle.

but put a BIG cam in there where you have 8-11 inches in neutral but only 6 or so inches in gear, the low vacuum, most likely pulsing up and down 2 inches, is going to make you idle timing bounce all over the place and cause all sorts of idle problem.

so yes, there IS a problem with using manifold vacuum depending on what you are running