I have a 79z with a 350 .40 over, rpm edelbrock intake, holley 600 carb, headers, .488 lift crane cam, full exhaust, etc-- and a gm hei distributor. The car is running pretty rough/rich. I checked the timing (with vaccum advance line plugged) and its at 8*. Once I hook the vaccum advance back up, idle raises a decent amount (not ALOT, but noticeable from exhaust note) and it goes to about 22*. Is this normal? or is my motor setup throwing the vaccum advance off on distributor? The car sounds alot healthier with vaccum hole plugged, but I was told to leave the line hooked up, unless it was more of a "pure race" car.

You have a 14 degree vacuum can. Sounds about normal to me. With vacuum hooked up to a manifold source you will see vacuum at idle.

I'd be more concerned with how much mechanical timing you have/where it comes in/total timing/etc. Seems like your vacuum setup is just about right...not too much but not too little. If it doesn't ping under light throttle I would say its pretty close.

You should always run vacuum advance on a street car.

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70 SS 454 CI Dynoed 684 HP, 702 TQ All Aluminium Fuel Injected Small Block , plus 200 - 500 HP NX nitrous system.

thanks guys. This is my first "real car" my last car was a 97 monte carlo z (ran 15.0 which was tooooo slow) . I'm used to using my laptop to set timing, not a timing gun :/ Adjusting a carb is going to be a challenge as well, can't swap fuel injectors and program fuel tables anymore http://www.nastyz28.com/ubb/frown.gif

You need to put more timming in that engine. 8* aint enough. It's a good starting point though

really you need to set total timing w/o vac. advance. To do this you will need a dail back light, or timing tape on the damper, or a degreed damper.

Rev enginge till the timing stops advancing. Read what it is, and look at what RPM it stopped advancing at

Set total to 36*, and change the springs in the dist. to get the timing fully advanced at 3,000 rpm

The sprngs are under the rotor button, take the button off and you'll see them. To get the lighter springs you'll need to buy a dist. recurve kit (less than $5)

In gen, you want the timing curve to start advancing at around 700-900 rpm, and be fully advanced by 2800-3200 rpm

Again a good starting for total is 36*, if you don't get any ping go up a degree at a time, till you do.. If you ping at 36* go down 1* at a time till it stops pinging

Agree with night rider

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1972 Camaro 350 factory heads 1.94/1.5 street driven full interior
93 octane everything works 7.59
89.54 mph
Never owned a trailer never will!

Maybe you should modify with an aftermarket FI.$$$

8* is enough if you already have 28* mechanical. All depends on what you have mechanical and until you find out we can't make suggestions on simply initial.

I would consider the total to be critical,
disconnect the vac advance set total around 36* @ 2500-3000 rev it on up find your total
mechanical advance if its way up there like 4000 then add some lighter springs but get the total in by 3000, then play with initial timing each time you make adjustments re-check the total

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1972 Camaro 350 factory heads 1.94/1.5 street driven full interior
93 octane everything works 7.59
89.54 mph
Never owned a trailer never will!

which port should the vacum advance be hooked up too the one under the throttle blades or the one on the metering black on top Thansk henrik

Most old school small blocks like at least 10-12 initial, with a total of 36 +/-2 degrees all in by 3000. Like others have said, some '70s HEI distributors came with as much as 28 degrees mechanical. You want more initial for good off the line performance. I like setting my HEI's at 22 degrees mechanical, even if it means MIG welding the slot and starting over.

And you DO want to keep the vacuum advance. It helps driveability a LOT.

ZFactor - Connect vac advance to ported. If the rpm's still come up when you connect the vac line, then you have the throttle blades open to far at idle, which opens another can of worms...

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79 Z28 Bought new, honeymoon ride, same wife, same car.

<font face="Arial,Verdana" size="2">Originally posted by CorkyE:
ZFactor - Connect vac advance to ported. If the rpm's still come up when you connect the vac line, then you have the throttle blades open to far at idle, which opens another can of worms...

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The 'rough & rich' comment in the 1st post made me think the carb is misadjusted.

What is the order of events, set timing or carb first?

Timing first, this can dictate idle. I'm believing the carb needs a "few" adjustments also.

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79 Z28 Bought new, honeymoon ride, same wife, same car.