Silly Timing ???????

[DesertRat]

Well it was a battle, but the 67 Notch is back together & running well. The book says to set the timing on the 273 2V @ 10 deg BTDC. My question is do I set it with the vacume advance line to the distrubutor connected or disconnected? I tried it both ways and it is now set @ 10 BTDC with the vacume line connected. On the test drive it seemed a little slugish, like it might be too retarded, much like it's driver;)
TIA-Rat :salut:

 

[Mopower71]

Was the engine built up stock?
Timing is set with the vacuum line disconnected.
Also the vacuum to the adv. should be a ported source. make sure when you set the timing the engine is idleing low, so the mechanical adv. is not coming in

 

[DesertRat]

Yeah, the engine is bone stock. The vacume source is the stock position on the carb base. I thought the engine was a bit retarded. I will reset timeing and try it again. Thanks for the input.

 

[racecarbob451]

I dont know were the rumor started that vacume advance vac source is Ported . BUT its wrong. You always set initial with the vac hose disconnected because if you didnt the distributor would be adding extra timing. And thats with vac hose to manifold vacume. If it were ported vac it wouldnt matter as there is no ported vac till you are off idle. Next you want the vac advance to drop off as load increases and rpm rises or you get detonation. If its hooked up to ported vac. It will pull in more timing plus the mechanical. Giving you a total of some were in the 50s and thats way to much timing under load.Vac advance is a milage thing for light loads and crusing when the vac is high.Some smog cars had a dual diaphram advance unit that had both ported and manifold vacume to it. Those were to retard the timing under certain conditions but that is the only time you hook ported vac to a vacume advance unit.

 

[green67cuda]

that sounds backwards to me.....seems you'd want it ported, so that when you tromp it off-idle, you will get advance. if you hook it up to manifold vacuum, when you stomp it, vacuum drops and your advance goes away.
ported, it would depend on how much accelerator you give it to determine the amount of vacuum....light acceleration will advance slower, heavy acceleration will advance quicker, because you'd get more vacuum signal....

THEN, on dual port vac advances, the retard nipple would go to manifold vacuum so that if you were going at speed and let off, the manifold vacuum increases, which pulls the vac advance down (decreases advance)

as far as total advance, you'd set the vac and mechanical to have a total of 34-36, and you'd have to set the transitioning of it from vacuum to mechanical by adjusting the vacuum advance and the mechanical advance

 

[OUTLAW]

ported vacuum is a vac port controled by the throttle plate .At an idle there shouldnt be any vacuum signal then as the rpm increases the vacuum increases this usually done by the port being just over the throttle plate then as the plate pivots it opens the port to expose the port to manifold vacuum. a simplified explaination. At least thats the way it has been for the last 30 years

 

[dgc333]

Outlaw you are correct. With very few exceptions the vacuum advance on old mopars is connected to a ported source.

If you have vacuum at idle then the throttle blades are open to much exposing the port. Whether the line to the distributor is connected or not should not make a difference. If it does I would be looking for what the problem is.

Also, the vacuum advance is used to add timing under low load cruising conditions to improve economy. When the throttle is opened abruptly and under WOT acceleration manifold vacuum is close to zero well below the point the advance pot will respond to. Once you settle back into a steady state throttle position and manifold vacuum increase the pot will add timing.

Timing verse rpm is controlled by the springs and weights in the mechanical advance. From a pure performance stand point the vacuum advance is not required and you will find that pure performance distributors do not have it.

 

[DesertRat]

I was suprised to see this pop up again. I reset the timing with the vacume advance disconnected and the car runs like a rocket. I think it wants todays premium fuel as I noticed some very minor pinging. I put new radials on it and had the front end alligned and it is now on the road as my daily driver. I have road tripped it twice to the grandsons baseball games and this weekend I will Round trip about 250 miles for the big test. I will be carrying my tow strap and cell phone Next up, dual exhaust!!!!!
Rat