WTB: 3-port Distributor Vacuum Advance

[The Professor]

Tested mine over the weekend and all three diaphragms tested bad. Let me know what you've got for me!

[Petros]

you car should run fine without it. just block off the vac lines (or they will become a vac leak). the function of the vac advance is to advance the timing when the car is an a steady state part throttle condition when the fuel/air ratio is lean. the flame in the combustion chamber moves slower in a lean mixture and advancing the spark will improve fuel economy a little bit. On the three port vac advance, it is also used to retard the timing during certain running conditions to reduce emissions.

Neither of these conditions will affect routine driving, you will not feel any effect when you drive it. It is perfectly acceptable to just block it off until you can find a replacement. you might also consider cutting it open and replacing the diaphragm. I think there was someone on this forum that tried that. It can be done and that is a better solution than pay $300 for a replacement even if you can find one.

[irowiki]

Yeah I think a one or two port would work just fine in your case.

I did a lot of research and the only part you're really concerned about is the advancement of timing under load.

Also the three Port I believe is so the HAC can tee into it.

the one side is the advanced side and the other side of the retard side and we would just need to figure out what side the HAC need so you could just use a splitter on a two-port if you find one.

[Petros]

when the HAC leans the mixture for higher altitude (over about 7000 ft as I recall), it will also advance the spark because the leaner mixture burns slower.

if you rarely drive above that elevation you can do without the HAC, and remove it all.

[The Professor]

The car doesn't drive fine with the ruptured advance diaphragms. The engine REALLY doesn't like to rev out, once you're rolling it takes AGES to crawl to redline. When the distributor was off a tooth and base timing was around 30 degrees, the engine was much, much happier to rev.

I'd really like to find a good, working, used 3-port vacuum advance module and avoid any modification to the systems. Just trying to get back to a solid baseline with the car.

[irowiki]

Well yeah if they are ruptured there will be a major vacuum leak. So you'd want to cap off those lines while you wait.

For what it is worth, I never found a good used vacuum advance through all of the Tercels I owned or the junkyard ones I pilfered. I snagged like 6-8 of the last new ones off rockauto for $25 each then resold them all to forum members back in like 2015!

Also, after Peter refreshed my memory, you'd be able to find a two port and then tee your HAC into the "lower" port, meaning the port closest where it inserts into the distributor.

https://www.ebay.com/itm/Distributor-Va ... SwI~BbnKr2

That one would work for you.




AH! A three port one!

https://www.ebay.com/itm/1983-1988-Toyo ... SwssRc9D6B

[dlb]

Also, after Peter refreshed my memory, you'd be able to find a two port and then tee your HAC into the "lower" port, meaning the port closest where it inserts into the distributor.

This is true but don't forget that you would need to add a restriction device to the third port, which I believe goes to the HAC on your US T4's.

[Petros]

you are not really modding the system, just capping off the unused ports. A leaky vac advance is a large vac leak, cap it off for now, set your timing, and it should drive fine. if not, likely it is something unrelated to the vac advance.

[The Professor]

So cap off the nipples on the vacuum advance module and plug the vacuum hoses until I find a replacement? Or can I just leave the hoses connected (will there be a vacuum leak with the hoses still connected?)

[irowiki]

Yes, the advance itself is likely causing the leak, just disconnect it completely, and plug the three lines, no need to cap the advance.

The bottom two ports actually share the same diaphram! There should also be a check valve from the manifold -> advance so the HAC doesn't just suck air.

DLB is correct, you'd want to add a jet into the line going back into the HAC if you end up finding a two port. Though I don't think the restriction on the HAC port is quite as bad as a jet, if I recall.

[dlb]

So cap off the nipples on the vacuum advance module and plug the vacuum hoses until I find a replacement? Or can I just leave the hoses connected (will there be a vacuum leak with the hoses still connected?)

Disconnect the hoses and plug them. Yes, they will still leak if connected to the advance unit. You don't have to plug the ports on the advance unit though since they will not be connected to any sources of vacuum.

[garyfish]

there's one 2-port vac advance on Amazon.com for $62 plus shipping... "used -- like new"

https://www.amazon.com/Standard-Motor-P ... automotive

[irowiki]

there's one 2-port vac advance on Amazon.com for $62 plus shipping... "used -- like new"

https://www.amazon.com/Standard-Motor-P ... automotive

Actually the picture is at a bad angle, that's a three port!

https://www.summitracing.com/parts/smp-vc360

I could tell because the exposed "lower" port has the HAC restriction.

[garyfish]

^^^ good sleuthing there

[The Professor]

Ok, I'm in the process of chasing down these leads, thanks guys!

I'll report back what I find.