Help with timing issue

[DoubleL]

Thanks for your input in advance guys.
I have a new HEI with the coil in the cap. It has full 12 volt power.
I set the timing at 4 degrees advanced with vac advance plugged but when I reconnected it the timing jumped and advanced past the "A" setting on the indicator. It probably advanced 16-18 degrees when I plugged it in. I ended up lowering the timing to "0" so it wouldn't advance so much. The truck idles and revs great but totally falls on it's face going up hills.

What should I set the initial timing to? What should it jump to when I hook up the advance. I have the advance hooked to a port on the manifold is this right?

Any advice would be appreciated. Also it has been verified that the timing mark is correct at TDC.
Thanks guys!!!

[geezer#99]

Sounds right. 'A' means advanced which means btdc. Unplug your vacuum line from the distributor, set your initial at 12 and plug the vacuum advance back in.If you plug it into full time vacuum your timing will advance. If you plug it into porte then it won't advance till you open the throttle.
Ported is on the plug on the top passenger side of your holley. Advanced would be at the bottom on the throttle plate.

[DoubleL]

Originally Posted by geezer#99

Sounds right. 'A' means advanced which means btdc. Unplug your vacuum line from the distributor, set your initial at 12 and plug the vacuum advance back in.If you plug it into full time vacuum your timing will advance. If you plug it into porte then it won't advance till you open the throttle.
Ported is on the plug on the top passenger side of your holley. Advanced would be at the bottom on the throttle plate.

Okay so I want it plugged into ported right?

[luvbowties]

Originally Posted by DoubleL

Thanks for your input in advance guys.
I have a new HEI with the coil in the cap. It has full 12 volt power.
I set the timing at 4 degrees advanced with vac advance plugged but when I reconnected it the timing jumped and advanced past the "A" setting on the indicator. It probably advanced 16-18 degrees when I plugged it in. I ended up lowering the timing to "0" so it wouldn't advance so much. The truck idles and revs great but totally falls on it's face going up hills.

What should I set the initial timing to? What should it jump to when I hook up the advance. I have the advance hooked to a port on the manifold is this right?

Any advice would be appreciated. Also it has been verified that the timing mark is correct at TDC.
Thanks guys!!!

Hope others will chime in; but iirc, at least on newer v-8's, timing is set on HEI's with the vac adv hooked to an unported source from our carbs--meaning pulling even at idle. [The modules have increased and decreased 'dwell-curves' built in, which changes timing as dwell changes.]

Sounds like your timing is retarded due to being set on zero w/adv unhooked and plugged. Maybe set it just as you did, except on 4 deg; then up it to as much as 8 degrees, test-driving up those hills at each setting again--over-looking what it jumps to when you re-hook vac. If it ever 'kicks back' on your starter, or if it spark-knocks, lower your setting gradually until that stops. You may also benefit from connecting your vac to a 'ported'(not pulling until throttle is opened) source on your carb.

Your HEI possibly needs a re-curve kit, some which decrease overall advance-swing; but I wouldn't consider one until I tried these suggestions first. What brand/year is it built for?
HTH,
sam

[DoubleL]

This Hei is for my specific engine (I-6 292)

[luvbowties]

Originally Posted by DoubleL

This Hei is for my specific engine (I-6 292)

Sorry, I was confused, and erred above. What had me confused was the fact that newer v-8's w/HEI run with full manifold vac to the advance, this being different from earlier point-types--dunno why. Timing is still set on them w/vac unhooked and plugged.

As others have advised above, your 6-cyl prolly runs better with vacuum connected to a ported source.
Pls forgive,
sam

[fleetsidelarry]

Originally Posted by DoubleL

I set the timing at 4 degrees advanced with vac advance plugged but when I reconnected it the timing jumped and advanced past the "A" setting on the indicator. It probably advanced 16-18 degrees when I plugged it in.

That's how it's supposed to function, DoubleL. There's nothing wrong with pulling that much advance at idle unless you are concerned with meeting emissions requirements and have all the other emissions equipment. the vacuum advance mechanism also retards the timing when the engine demands it. when you put a load on the engine, vacuum drops momentarily, causing a corresponding drop in the amount of advance.

once off-idle, it shouldn't matter whether you're on ported or full manifold. I'd say try it both ways, starting with your original 4° initial setting.

[maxwoof]

My experience with the older trucks is that the vacuum source is ported - the source is just above the butterfly in the carb. When you step on the gas, vacuum becomes present and the vacuum signal to the distributor advances the timing.

There are distributors out there that use vacuum from under the butterfly (constant at idle) to retard the timing at idle. In this case, when you step on the gas, vacuum drops, and the signal to the distributor allows the timing to advance.

In either case, the timing should advance as you accelerate. I would think that if you are not sure how your distributor should work, put a timing light on and observe the timing at idle. Apply vacuum to the distributor and see how timing is affected. If it advances, then it needs vacuum to increase off idle to advance timing as you accelerate. If the timing retards when you apply vacuum, you need vacuum to decrease off idle to advance timing as you accelerate.

In the first case, the distributor should have no vacuum at idle, in the second case it should. Hope this helps.
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[fleetsidelarry]

there is only one "vacuum" signal that increases as you accelerate a vehicle: venturi, a weak signal used to operate carb secondaries. both "ported" and "full manifold" ports are MANIFOLD. Manifold "vacuum" decreases under acceleration. This takes vacuum advance out of the picture under acceleration, which is how it's supposed to work. If a distributor reacted to a sudden decrease in vacuum with a sudden increase in advance, you'd get detonation. Under load (low manifold vacuum) the timing is controlled by the mechanical curve which is solely rpm dependant. I can't imagine an automotive distributor based solely on vacuum signal, that advances as vacuum drops.

[fleetsidelarry]

to amend what I said above, I can imagine a distributor using the vacuum signal to retard, as maxwoof stated, which allows the mechanical to work as intended under acceleration. I have heard of such. but upon return of the signal at cruise it would seem that it would retard the cruise timing, which seem counter-productive.

I believe I've taken us off the original subject.

[maxwoof]

You are correct re: mechanical advance. The vacuum advance is there to help you out until the rpms kick in. My 62 k20 pulls vacuum from directly above the throttle plate. At part throttle it draws vacuum and advances the breaker plate. You can watch it happen as you rev the throttle. By the time it is wide open, no more vacuum and the breaker plate is back at rest.

My 69 Porsche has vacuum retard. It pulls vacuum from under the butterfly, and when you step on it, the breaker plate springs back to advance. The opposite of the truck.

Both principles are the same. The vacuum assists until centrifugal kicks in.
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[DoubleL]

So I set the timing at 4 degrees advanced with the vac line plugged. With manifold vacuum it advanced the timing so far at idle the truck would barely run. It ran horribly on the road popping and losing power under load. I switched the line to a ported vacuum and it stayed at 4 degrees when I hooked it up and drove great! So for my truck and new distributor it was ported as the only option. I do have a sputter on acceleration but I think it might be a carb issues.

[fleetsidelarry]

Thanks for getting back to us, DoubleL. sounds like the chevy 6 cylinders don't like as much idle timing as the small blocks though I don't understand why there's a difference off-idle between the ported and full-manifold. doesn't matter, if you're happy

[awbrown]

There have been other threads with this question , I searched my old threads but must have deleted it .. Most chevys will run best with manifold vacuum, the reason being is a lean mixture burns slower and needs more lead , and a rich mixture burns faster needing less ... timing , on chevys is always set with vacuum line off the distributor and plugged.. some of the time I ad adavance 2 degrees at a time til I it pings or detonates under load and then back it up 2 or 3 degrees and leave it ... you can limit the amount of vacuum advance it has with new can that is adjustable if you get a little rattle as you tip the throttle in ,or change the power valve / spring to richen it up depending on what carb you have ...