i asked on another thread about this, then i thought i fixed the problem, but i was wrong......so i figured id make a new thread instead of completely hijacking that one.....heres the deal, i have a 460 with a 780 4bbl Holley vacuum secondary, and stock Duraspark II ignition.... before i replaced all the gaskets and timing chain in this engine, i ran my vacuum advance direct off the manifold and it worked great...until the other day i didnt have a ported vacuum at the time to hook to.....now that i got it back together i cant hook up vacuum off either port...if i put it on the direct vacuum it dies as soon as vacuum hits the hose, if i hook it to the ported one on the carb it spits, backfires and dies when you hit the gas...i was watching the timing light when i bumped the throttle and the scale disappeared!!!! too much vacuum, so i adjusted the module all the way back and its not as bad but it still does it.....keep in mind, i already made sure its not the carbs fault, its not flooding out, its over advancing.....i have tried moving the distributer back and forth a few teeth to see if i was off, but im not, it works best in the original postion....without the vacuum on at all she has all kinds of power wants to burn the tires off, but it stumbles without that advance working right.....i even put on a different vacuum module to see if that was it, i thought it was working right when i put it on, but apparently the clip broke inside and it wasnt hooked up when i was test driving it....im stumped guys, i even (dare i say it) used my mouth for vacuum to see how much vacuum it needed to kill it, i barely had to use any force at all to pull the advance way over 30 degrees.....my last hope is one of those little inline vacuum disks, those are vacuum limiters arent they??? i hope its that simple......ok im done writing this book, any replies will help thanks...........

 

It sounds like the springs that under the pickup coil plate have come off. These are the spings that control the advance. I have seen this before. You have to take the distributor apart to see/fix them.

 

good idea, but they are all in place..........when i had the dizzy out i heard a rattle, so i tore it down and seen that the mechanical advance was the noise maker even though its not broke.....thanx for the input.....

 

Yank the dizzy and recurve the advance to whatever you want it to be without using vacuum and then don't hook up the vacuum. Your mileage may suffer slightly, but I doubt you'll notice.

 

i thought about that, but i have no idea what to look for when recurving them.......any insite on that one?? or does anyone else have any ideas?? this is really bugging me because before i changed the worn out timing chain i could hook it up to the direct manifold vacuum and it would smooth the idle out and ran great..............im so confused, ive never seen this problem before........

 

it still sounds like a carb problem cause the ported vacuum should have no effect on timing or how the engine runs till you rev it. i think you might be mistaken the manifold for ported vac. check if you have any ported vac at idle, you shouldnt.......

 

you might re-read my original post....it says this among other things...

aint no mistake, ive been running this engine for 5 years and i just tore it down, and did a mild overhaul.... and i know what vacuum is what...i just added the ported vacuum because my Holley didnt have one, so i had to install another metering block so i had one.......its defintitly in the advance because as soon as it gets ANY vacuum it kills it....i can barely (dare i say) suck on the advance line and the timing goes nuts and over advances, ive had 3 different advance modules on there with the same affect........im about to lose it and by a whole new distributer setup...

 

You need to put a timing light on the engine, with the vacuum hooked up and see what happens to the timing when you advance the throttle. Something is not right. If the metering block you installed in the carb is not compatabile with the carb (they all are not interchangable) you will get all kinds of strange stuff. Just off idle the ported vacuum should give you very little added advance, maybe 5 degrees at most, if that much.

As to recurving the dist. If you rebuilt your engine, you can easily do the recurve a dist. Check here for instructions and best of all pics.

http://www.reincarnation-automotive....ons_index.html

 

i would get a used distrib. from a junk yard or somewhere. thats got to be the problem, unless the timing is of at the chain.