I think this is a very clever system. A mechanical solution right before computers took over fuel/air delivery. It simply adds more air to the idle,primary, and secondary circuits while advancing timing at altitude.
Aisan HAC
- Thread starter mwebfj60
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- #2
The HAC valve took a bit for me to figure out. What had me baffled was that the port circled that hooks to manifold vacuum via a T and check valve doesn't hold vacuum when at low altitude. Come to find out it's a designed vacuum leak from the factory. I can envision the debates that took place in engineering.
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- #3
When at low altitude, the three upper ports all hold vacuum independently of each other. The port circled in white is just always open to atmosphere.
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- #4
I think of the bellows inside the HAC like a balloon, kind of like taking a bag of chips up to the mountains...when you get there the bag's about to pop. So the bellows start expanding as altitude goes up. The FSM range is 2570ft to 3930ft. So I think it's a fairly linear expansion where the vacuum port and the three upper ports start getting effected at 2570 and are fully functional at and above 3930ft. Very clever...so you are adding proportional amounts of air and vacuum advance through those ~1400 ft.
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- #5
So when it is at altitude, the bellow closes the vacuum port (passage listed as Port A) and allows vacuum from the fuel filter to pull the secondary diapghram and advance timing an additional 6 degrees...compensating for the slower burn. The check valve (one way) keeps vacuum on the circuit even if the motor is shut off...the vacuum should only release when you drop in altitude and the bellow contracts, opening the vacuum port back to atmosphere.
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- #6
When at altitude, the passage listed as Port B opens connecting all 3 upper ports to atmosphere. This provides additional air to the primary slow, primary high, and secondary high circuits. The primary is in red, secondary blue. The high circuit air goes right into the top of the venturis and the primary slow provides air right into the idle circuit.
micruz60
Unleaded Regular
Thanks for the lesson at Land Cruiser Univ.
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- #8
When I desmogged, I decided the designed vacuum leak needed to be fixed. My solution was to use the two port Nippon Denso vacuum switch and control the vacuum off the gas filter with it and a switch in the dash. When I head to altitude, I flip the switch at around 3,000ft and the HAC functions as normal. When I head down, I turn the switch back off.
4Cruisers
SILVER Star
Thanks for the write-up. So there's no additional benefit above 3,930 feet. My driveway's 3,310 feet higher than that.
I've always thought that one day I'd add HAC to one or both of my FJ40s, each has a '76 2F, and both will soon have FJ60 distributors. So to get that to work I'd have to also go with FJ60 carburetors?
I've always thought that one day I'd add HAC to one or both of my FJ40s, each has a '76 2F, and both will soon have FJ60 distributors. So to get that to work I'd have to also go with FJ60 carburetors?
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- #10
That's a good question...didn't the 77' and later CA carbs have an option for HAC? The CA distributors of that timeframe were dual vacuum advance I believe.
4Cruisers
SILVER Star
I've already got one good spare FJ60 carburetor, along with a spare HAC and extra FJ60 vacuum stuff, so might give it a try on my '76 FJ40. I should have the FJ60 distributor installed in the '76 this week. BTW, thanks again for getting me over the hump with getting the distributor ready with your response to my post yesterday. It's all cleaned up and free of any rotor assembly binding on the shaft. Centrifugal and vacuum advance appear to be functional.
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- #12
Glad to hear it. Gotta love Mud, folks on here have helped me with a lot of tips. Let me know if you're going to sell the old carb off the 40. I would like to spelunk through one.
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- #14
You got it. The 3 ports for air are going to open by themselves. I just didn't want the vacuum leak since I'm at about 130' most of the time.
Nice setup and a good alternative since the HAC valve is NLA.
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- #16
If my HAC ever goes bad, I plan to run a tee off the vacuum line (the one leaving the Nippon switch) to a VCV that allows the air to flow for the three ports when you flip the switch.
Resurrecting an old thread...
@mwebfj60 - my truck will never see anything north of ~2000ft. Could that lower HAC line just be plugged?
This makes me wonder how hard it would be to put the top of my old Aisin carb on my Trollhole body and get HAC working with my desmog...or to just do a little drilling and put those two ports in the Trollhole...
That's assuming I don't just put TBI on my engine, of course.
That's assuming I don't just put TBI on my engine, of course.
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- #19
You got it, plug the port on the carb base and 3 prong filter.
Just remember that all the very small designed vacuum leaks in the 2F ancillary systems were accounted for in the carburetor jetting and idle mixture setting from the factory. Plugging them all up will make the engine run richer than ideal. The designed vacuum leaks are not evil or harmful.