Webers and HAC High Altitude Compensators
#1
Registered User
Thread Starter
Webers and HAC High Altitude Compensators
In discussing Weber conversions with another member here the question of tuning a Weber for altitude came up. Toyota already has a fairly simple looking devise attached to their Aisan carb’d trucks – the High Altitude Compensator (HAC). It seems to be set up to do subtle - on the fly - adjustments.
I haven’t studied it but it looks like it advances and/or backs off timing via the vacuum advance. But, I believe, one vacuum hose goes to the charcoal canister and I’m not sure what that accomplishes. I also presume it somehow senses the air pressure changes, but I’m not sure how. It seems to effectively “tune” for altitude on the fly. But I strongly suspect it is NOT a substitute for initially tuning a Weber for the attitude you normally drive at.
Thinking out loud here, I also wonder if it senses air pressure changes due to weather conditions.
I think it is a pretty useful devise for those who travel between lower and higher altitudes. For example; I live at 3545 ft, but when I travel out of the valley I live in, no matter what direction I go, I have to go up at least 2000 ft. Also, Flagstaff, which is not far from me, is at nearly 7000 ft. My truck doesn’t feel like it has any problems when driving at those increased altitudes. I imagine the HAC would be equally useful on a properly set up/tuned Weber conversion.
So, my questions are:
1) Has anyone hooked up the HAC on their Weber conversion? Pictures please.
2) Has anyone taken one apart and have pictures of an HAC?
I haven’t studied it but it looks like it advances and/or backs off timing via the vacuum advance. But, I believe, one vacuum hose goes to the charcoal canister and I’m not sure what that accomplishes. I also presume it somehow senses the air pressure changes, but I’m not sure how. It seems to effectively “tune” for altitude on the fly. But I strongly suspect it is NOT a substitute for initially tuning a Weber for the attitude you normally drive at.
Thinking out loud here, I also wonder if it senses air pressure changes due to weather conditions.
I think it is a pretty useful devise for those who travel between lower and higher altitudes. For example; I live at 3545 ft, but when I travel out of the valley I live in, no matter what direction I go, I have to go up at least 2000 ft. Also, Flagstaff, which is not far from me, is at nearly 7000 ft. My truck doesn’t feel like it has any problems when driving at those increased altitudes. I imagine the HAC would be equally useful on a properly set up/tuned Weber conversion.
So, my questions are:
1) Has anyone hooked up the HAC on their Weber conversion? Pictures please.
2) Has anyone taken one apart and have pictures of an HAC?
#3
Registered User
Typically I will remove a vacuum line from the manifold. Just a small one. Maybe if you were to put a small 2 with a little filter If you think dirt is a huge issue, I don't). You can lean out the fuel mixture that way. It really helps out when up in the mountains. Most of these older trucks and cars with altitude compensators, the compensators don't function as they should. You could do the same by grabbing a normally closed VSV, then have a small signal wire open it when you want to.
#4
Registered User
I am still learning about carburetors, but here is how the High Altitude Compensation System is hooked up on a factory AISIN carburetor (From my 1987 Toyota Truck and 4Runner Repair Manual).
My truck does not have one, being I am only about 350-400 feet above sea level.
I don't have a Weber to compare to, but I suspect the original High Altitude Compensation System is not compatible with the Weber.
My truck does not have one, being I am only about 350-400 feet above sea level.
I don't have a Weber to compare to, but I suspect the original High Altitude Compensation System is not compatible with the Weber.
#5
Registered User
Thread Starter
I am still learning about carburetors, but here is how the High Altitude Compensation System is hooked up on a factory AISIN carburetor (From my 1987 Toyota Truck and 4Runner Repair Manual).
My truck does not have one, being I am only about 350-400 feet above sea level.
I don't have a Weber to compare to, but I suspect the original High Altitude Compensation System is not compatible with the Weber.
My truck does not have one, being I am only about 350-400 feet above sea level.
I don't have a Weber to compare to, but I suspect the original High Altitude Compensation System is not compatible with the Weber.
Does your manual have diagnostic / troubleshooting info on the HAC?
#6
Registered User
My manual does have the diagnostics section for the High Altitude Compensation System.
I will post those pictures up tomorrow.
I will try to scan them as my camera does not like taking pictures of paper very well.
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