FZJ73 High Altitude Compensator & Carb Tuning (1 Viewer)

[thebill]

I just bought a 94 FZJ73 and am trying to get some things figured out before it arrives.

I live in NM at around 7000' and for the foreseeable don't anticipate going much below 4000' (still above the lower threshold of 3500' where the HAC kicks in). What I haven't been able to find much info about is if the HAC (assuming it works as was originally intended) eliminates the need to adjust the carb for elevation. I've read plenty about how the HAC works and how to adjust the carb for elevation but this one piece of the puzzle is still unclear.
If it's recommended to rejet the carb, what is/are the recommended jet(s) for this elevation range and how would the HAC affect the tuning process?

Thanks!

 

[OGBeno]

I just bought a 94 FZJ73 and am trying to get some things figured out before it arrives.

I live in NM at around 7000' and for the foreseeable don't anticipate going much below 4000' (still above the lower threshold of 3500' where the HAC kicks in). What I haven't been able to find much info about is if the HAC (assuming it works as was originally intended) eliminates the need to adjust the carb for elevation. I've read plenty about how the HAC works and how to adjust the carb for elevation but this one piece of the puzzle is still unclear.
If it's recommended to rejet the carb, what is/are the recommended jet(s) for this elevation range and how would the HAC affect the tuning process?

Thanks!

@FJ40Jim

 

[FJ40Jim]

AFAIK, all 1FZF engines have a HAC valve connected to the carb. The HAC is supposed to automatically open/close as the vehicle passes thru ~4500'ASL, allowing a small air leak at high altitude to effectively lean out the mixture. Unlike the HAC system we saw in the US on 81-87 carbs, the 1FZ HAC valve is not connected to the idle circuit, so the idle mix should be adjusted per the FSM during the annual tune-up.

 

[thebill]

AFAIK, all 1FZF engines have a HAC valve connected to the carb. The HAC is supposed to automatically open/close as the vehicle passes thru ~4500'ASL, allowing a small air leak at high altitude to effectively lean out the mixture. Unlike the HAC system we saw in the US on 81-87 carbs, the 1FZ HAC valve is not connected to the idle circuit, so the idle mix should be adjusted per the FSM during the annual tune-up.

Fantastic. Thanks @FJ40Jim
Is the HAC a part that can be maintained? ie tested and rehabbed as needed?

 

[FJ40Jim]

Test procedure is in FSM. The HAC valve is a cheap piece of plastic that fails with age. I try to avoid using them.

 

[JuanJ]

Fantastic. Thanks @FJ40Jim
Is the HAC a part that can be maintained? ie tested and rehabbed as needed?

Hello,

The HAC has a filter element that can be cleaned using circuit cleaner. It opens in two halves; one has the filter element.

Clean the element once a year. Other than that, it is maintenance free.

It is also possible to change the entire part if it is available.

There is a tuning procedure that involves a CO meter and the mixing screw. It is also possible to tune without the meter. Regardless of the procedure, make sure the engine idles at 650 (plus or minus 50) rpm when it is complete.

At high altitude it is better to have the mixture as lean as possible for smooth operation.





Juan

 

[thebill]

Hello,

The HAC has a filter element that can be cleaned using circuit cleaner. It opens in two halves; one has the filter element.

Clean the element once a year. Other than that, it is maintenance free.

It is also possible to change the entire part if it is available.

There is a tuning procedure that involves a CO meter and the mixing screw. It is also possible to tune without the meter. Regardless of the procedure, make sure the engine idles at 650 (plus or minus 50) rpm when it is complete.

At high altitude it is better to have the mixture as lean as possible for smooth operation.





Juan

Thanks Juan!