vaccum advance question

[BRAD ARTHUR]

hey maybe someone can help. i had heard you can run a temp switch to change the vac. adv. from manifold to ported vaccum , according to the temp. when cold adv with manifold vaccum and when hot adv. with proted vaccum. wasn't there something like this from factory certain years? coolant vaccum temp. switch? cts ? does anybody run with this setup? how could i go about pluming it or getting that kind of switch?

thanks for any help.

[ol' school power]

The switch you're looking for was a 70's band-aid approach to smog control when distributors had a real tight mechanical advance .
Connecting one is easy, but what are you trying to install it on?

[BRAD ARTHUR]

i've got a 304 edelbrock 600 1405, edelbrock intake, edelbrock cam, and a z&m hei. tring to fine tune it , on cold mornings doesn't want to idle very good. someone told me some run the vac. advance with this switch.
right now i'am running 12deg initial, 12 vac, 20 cent. if i remeber right i will double check that. w/ported vac advance. i've read some of you run 34-36 adv. on these motors? is that with ported or manifold vaccum?
my carb is jetted #18 on the chart-a 1430main &1451 rod w/ pink setup springs. accl pump linkage closest to pivot. i've changed main rods and spring and not alot of difference. plugs look real clean. doesn't seem like i can get it rich enough.
don't get me wrong it runs good, but can't get it to run best during cold and warm motor. if that makes sense. there is also a slight hesatation at take off with a cold motor. not always just once in awhile.
any one running this edelbrock stuff, what jets and what timing are you setting at?
thanks for any help just trying to fine tune with optimal performance.

[ol' school power]

If you've got 12 initial, that's more than enough to run good on a cold morning. I'd be looking more towards the carb.
Do you still have the hesitation when warmed up?
What thermostat are you running?
With the HEI, what are the plugs gapped to also which plugs?

[BRAD ARTHUR]

the hesitation is gone when warmed up. its only when i start in 2nd gear. i run a t18 and start in 2ndgear. 1st is too low.
the thermostat a robert shaw 180 deg
the plugs are gapped at .050"-.055". i forget which i set them at.

i m with you i guess its the carb, i rejjetted it from base line to a step richer and was ck the plugs. so i went richer and im at the richest the jet kit will go. i changed the main to a .104" jet and swap metering rods from 1459-1456-1451 leaner and richer makes no difference niether does the step-up springs. might try a lower main and go from there , but with the richest the plugs are still clean and look good.

[Goose]

Just an opinion here.. But If you have gone way rich on the jets/rods and youre not seeing a difference I would look at other areas. because on a 304 If I'm reading the charts right youre set up should be plenty rich. I would wonder if something like the choke not set rich enough would be causing your occaisional stumble cold and perhaps your secondaries are opening too slowly to be showing you the rich side of your set up??I would check your vacum reading and a few other basic tuning items cause changing out the secondary metering rods/jets isnt going to affect your off idle performance at all

I have been running a 1406 on a 360 for 9 years now and it will stumble once in a while when it is cold twice a month or so.. but the setup Im running is similar to yours and I am border line rich at WOT.

hope something helps in all this rambling..

[ol' school power]

You should have an adjustable vacuum advance.
Check inside the hole where the hose attaches for a 1/8" allen screw.
As far as plug color, you can also be running too hot a range.
You never said what you're running for plugs and range number.

[hohner0006]

Another area to consider is a vacuum leak.....running that big of jets and not fouling or sooting up the plugs would point to this. And it will seem to run reasonably well as you're adding enough fuel to make up for the extra air leaking into the motor. I chased a leak for 4 months before I found the source of the leak under the original cast-iron intake heat shield (obviously it won't apply to you aluminum intake). Just my .02

[FrankNB]

Ok, question relative to this... On a setup with a Q-jet, where's the best place to hook up the advance? Manifold or above throttle plate, or below throttle plate?

[ol' school power]

I'll say it depends on the individual engine and distributor as far as how it's setup.
Too much advance at the wrong time will cause detonation and power losses.
If you're running an aftermarket or modified stock distributor Then the ported source would probably be the safest bet. With full manifold vacuum, you would probably be pulling over 60 degrees on a cruise. At full throttle, there's no vacuum present at any of the ports and you're relying solely on mechanical.
Low compression stockers can get away with a lot more advance than an engine that's had mods done.
The 2 ports you're describing sound like the egr and distributor port. See which works better in your application.

[BRAD ARTHUR]

I CHANGED MAINS TO ORIGINAL BASE LINE FOR THE 1405. ADJ TIMING-IT WAS 10 INITIAL,20 VACCUM, 20? CENT. CHANGED IT TO 6INITIAL, 7 VACCUM, 20? CENT. THE VACCUM IS ADJ. AND WAS AT 5 TURNS OUT NOW AT 9 TURNS OUT. RUNS GOOD OVERALL, I 'M THINKING THERE IS A VACCUM LEAK AT IDLE IT WONDERS FROM 750 RPM TO 1100RPM. THE TIMING STAY PUT FUEL PRESSURE STAYS SAME.
1ST I THOUGHT IT COULD BE TIMING THE ROTOR SEEMED TO STICK IF YOU ROTATED IT CW ( WITH CAP OFF - BY HAND). SO I CHANGED THE ROTOR AND IT SNAPS BACK.
2ND ADJ IDLE SCREWS OUT- RICHER HELPS BUT STILL WONDERS
3RD CHECKING VACCUM IT WONDERS FROM 5" -15" Hg RUNS GOOD AT 15" (THIS IS WHERE IT RAN WITH THE RICHER MAIN JETS)
4TH PULLED THE BRAKE BOOSTER VAC LINE - RAN BETTER SO I CAPPED IT OFF AT THE CARB. STILL WONDERS
MY ASSUMPTUION FIRST I WAS WAY TOO ADVANCED, AND TOO RICH. ADJUSTED THEN NOTICED A WONDERING ONLY AT IDLE FROM 750 TO 1100. INCREASING IDLE ONLY HELPS THE TOP # WILL STILL GO DOWN TO 750. THOUGHT IT COULD BE DIST. THEN BRAKE BOOSTER. NIETHER. WHEN YOU COVER THE INTAKE PRIMARIES WITH YOUR HAND, RPMS INCREASE.
I'VE ALSO SWAPED STEP UP SPRINGS IN CARB AND DOESN'T HELP. FROM 3" BLUE SPRING TO 8" SILVER SPRING. WHAT IDLE VACCUM READING SHOULD I SEE AT IDLE ?
THANKS ANY ADVICE WOULD HELP

[ol' school power]

Holding your hand over the carb is increasing the fuel since the idle circuit can't keep up.
Springs should have no affect until the throttle is opened enough for the boosters to take over.
How far out are the idle mix screws so far?

[BRAD ARTHUR]

I HAVE TAKEN THEM OUT 3 TO 3.5 TURNS. I ALSO HAVE A 2" CARB SPACER . MIGHT TRY SOME EITHER OR CARB CLEANER AROUND THE SEALING SURFACES. DO YOU THINK I AM ON THE RIGHT TRACK WITH A VACCUM LEAK? WHAT WOULD CAUSE A IDLE SURGE THAT DOESEN';T SEEM TO BE TIMING OR FUEL RELATED ?

[ol' school power]

It may be, but then it could be a plugged fuel circuit if there's no leak under it. Do you keep a good air filter on it?

[BRAD ARTHUR]

THE FILTER NEEDS CHANGED ISN'T OVERLY DIRTY BUT COLLAPSED A LITTLE. WHAT SHOULD I LOOK FOR IN THE FUEL CUIRCIT ON A 1405 EDELBROCK?

[ol' school power]

There isn't a whole lot you can look at to see a problem. Spray anything around the carb. Doesn't matter what you spray. Water works just as good to determine if there's a vacuum leak.