I can say this for sure: if I make the tooling to rebuild the original vac unit, they will run $125-175 for the vac rebuild by the time I make the necessary internal parts to complete the rebuild, and make the tooling to be able to reassemble them properly. The aftermarket single vac units are inexpensive and can be modified to work properly. In my 13 professional years rebuilding distributors, as well as the 17 years prior doing it just for fun, I've never seen an application that needed a dual vac like this one. Its a 2-stage vacuum advance, which is just silly. under higher or lower vacuum, the unit should be able to apply the correct amount of advance at the correct vacuum level. Period. This setup makes no sense. Its overly complicated and even when it works as intended I don't believe its working as well as a good single vac unit could.
In need of a rebuilt distributor for my 1985 FJ60. (1 Viewer)
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If we could find a single that works, all of us holding our breath until our duel one dies, would be super stoked. Thank you for taking this project on.
FJ60Seth
SILVER Star
You currently have one of my distributors. If you’d like to install a single vacuum advance, please go ahead.
The Dual Advancers are for 80's smog control only before fuel injection and ECMs, and why Toyota took this complicated approach is anybody's guess.
If a readily available single pot diaphragm could somehow be retrofitted to these, that would be an engine-saver for many people, and I doubt even in smog-states, like I'm in, in Kalif, the tech would even know the difference. How it would effect smog output I have no idea, and would depend greatly on the degree of testing required per area, but can't be any worse than a non-functional advancer.
I'm sure the goal was that the first stage of vac at 8 degrees advance would give better emissions than the 20 total from both being in service. If you need to pass emissions, retard the timing. Make the engine run poorly. Lean out your idle mixture as well. Going from a dual to a single is no game changer. So far I haven't seen a dual vac unit with both diaphragms failed. Disconnect and plug the vac line from the leaking diaphragm.
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The function of the two stage vac advancer is covered in brief in post #45, and more in depth in various Mitsubishi, Honda & Toyota service manuals. They used it to get carbed engines through smog in the 70s-80s at different altitudes.
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Altitude may have been an excuse, but it works the same at any altitude. I wasn't aware that there was a separate import smog test at high altitude. Usually that was done in coastal facilities. All Toyota cared about was the certification so they could be unloaded and get out of customs. Cutting back timing was part of passing, and that can be done just as well by using ported vacuum.
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There is an altitude sensitive valve that changes position above ~4500', to add the 6* of timing from the second fitting on the canister. When EPA regs did an annual tightening in the late 70s, one of the changes was requiring vehicles to show compliance at sealevel and high altitude. It was no longer permissible to sell a vehicle with a hi-alt or a low alt calibration, or require a modification (adjusting idle mix or setting timing) to run clean at different altitudes.
Amusingly (to me, anyways), Mitsubishi left the HAC valves off the 2.6L engines around 1987?, but got caught failing smog at high altitude, so had to do a recall and put the HAC system back on a couple of years of affected trucks.
Amusingly (to me, anyways), Mitsubishi left the HAC valves off the 2.6L engines around 1987?, but got caught failing smog at high altitude, so had to do a recall and put the HAC system back on a couple of years of affected trucks.
this thread is gold 
So what you're saying is that likely 90% of all FJ owners don't need the valve because they'll never drive at 4500' or higher... That means they could all run better with a better single vac installed because the portion of the vac unit working at low altitude is NOT ideal, and if it was really right it would also lean mixture more at higher altitude. Knowing that there's a switch for altitude makes me like the theory behind the dual vac even less.
The other side of the coin is that the vac unit only helps the engine run leaner under low load, when emissions are already decreased.
The other side of the coin is that the vac unit only helps the engine run leaner under low load, when emissions are already decreased.
Unfortunately , I am part of the 10% that lives above 4000 ft. It is my hope that you will figure out a way around this nonsense as I live in Kalifornistan and have to play by their rules. Right now I live where I only have to smog on change of ownership, But I still need the vacuum advance working correctly. Thank you for your time,
I ran from sea level in Texas, to 6500+ In Raton NM and all the way up to 12,000 ft in Colorado with 12-14 degrees initial, a JimC recurved distributor and the large pod. I used 91 or better fuel the entire trip. I didn’t have the high altitude compensation valve connected.
I’ve found that it runs better on 89+ down here with less advance on the smaller pod(outer)
I was getting some detonation above 2500 rpm with the large pod. The tune is spot on now, but I’m not subject to emissions.
I’ve found that it runs better on 89+ down here with less advance on the smaller pod(outer)
I was getting some detonation above 2500 rpm with the large pod. The tune is spot on now, but I’m not subject to emissions.
That makes sense. Full vacuum applies 20 degrees of advance, which is too much for anything other than a small displacement, lethargic engine with very low compression and a horrible combustion chamber design. It should ping or detonate, unless you're at high altitude where its less likely. The outer pod only offers 8 degrees of advance, which is ideal most of the time, in most applications.
Without the vac hooked up, at 2500 rpm you should have about 25 degrees of advance (BTDC). More than that and your timing curve is problematic, and it WILL ping under load.
Without the vac hooked up, at 2500 rpm you should have about 25 degrees of advance (BTDC). More than that and your timing curve is problematic, and it WILL ping under load.
NeverGiveUpYota
Dare me.
I sent out a spare to Jeff, @distributorguy. I’ve been so busy pulling the engine I didn’t post photos of it. Amazing difference between the one before and two after. (The advance pot is brand new old stock I got lucky and found awhile back.) He was easy to communicate with and fairly speedy.
Curious to know how @FJ60Cam has made out? Did you add a single pot advancer to his as he requested to try?
Curious to know how @FJ60Cam has made out? Did you add a single pot advancer to his as he requested to try?
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mattressking
10 digits to freedom
NeverGiveUpYota
Dare me.
For those folks calling about my services, these are newer distributors than I usually rebuild. I'm typically ONLY a points guy, plus those engines are mostly built prior to all the SMOG stuff you;re trying to keep alive. The dual vac is strictly a smog thing BTW. If the timing curve was fixed to not be a smog curve, then a single vac will work great, which I don't have because the bulk of my efforts are on 1980 - 1920's distributors. My inventory is mostly Lucas, which doesn't help you guys much.
Both sides of the dual vac unit are not what you really need to cope with normal drivability. The primary doesn't offer enough timing, and the secondary is too much. A car single vac is far more likely to run well.
Both sides of the dual vac unit are not what you really need to cope with normal drivability. The primary doesn't offer enough timing, and the secondary is too much. A car single vac is far more likely to run well.
mattressking
10 digits to freedom
Generally correct except that the secondary port is for high altitude compensation which is what some of these folks need/want. Though I've found that I can get by just fine at altitude running without HAC.
I'm going to say it bluntly:
If the primary centrifugal advance wasn't so horribly F'ed up, both high and low altitude drivability would be worlds better. Get it? Vacuum only gets used under low load, which is almost never at altitude. Load is significantly higher due to a lack of oxygen. That's why your power is down 30% at 10K'. Higher load = no vacuum signal. Fix the primary timing curve. Adding more timing at altitude is not the best answer.
If the primary centrifugal advance wasn't so horribly F'ed up, both high and low altitude drivability would be worlds better. Get it? Vacuum only gets used under low load, which is almost never at altitude. Load is significantly higher due to a lack of oxygen. That's why your power is down 30% at 10K'. Higher load = no vacuum signal. Fix the primary timing curve. Adding more timing at altitude is not the best answer.
And I'll put this bluntly-
For whatever reason, the 2F on the FJ60 runs way better at altitude when the HAC system is functional (+6° extra advance added to all RPMs). Conversely, if that 6° extra advance is left on below 3000- 4000 ft elevation, the engine will ping. It may have been an emissions component to pass the idle test (full vacuum) at idle, but it's also a driveability improvement enhancer at attitude regardless of smog. Granted not at WOT, but alot of driving of these vehicles at least off road, is light throttle crawling. Engine vacuum is part of the equation.
No single stage vacuum advancer can perform as well at altitude and sea level as a dual diaphragm unit because the degree of advance required is not linear. It depends on the altitude.
For whatever reason, the 2F on the FJ60 runs way better at altitude when the HAC system is functional (+6° extra advance added to all RPMs). Conversely, if that 6° extra advance is left on below 3000- 4000 ft elevation, the engine will ping. It may have been an emissions component to pass the idle test (full vacuum) at idle, but it's also a driveability improvement enhancer at attitude regardless of smog. Granted not at WOT, but alot of driving of these vehicles at least off road, is light throttle crawling. Engine vacuum is part of the equation.
No single stage vacuum advancer can perform as well at altitude and sea level as a dual diaphragm unit because the degree of advance required is not linear. It depends on the altitude.
