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Old 07-29-2019, 06:13 PM
GWJeeper GWJeeper is offline
232 I6
Join Date: Mar 28, 2019
Location: Oklahoma
Posts: 31
Questions about Altitude Compensator and Vapor Canister

A lot of our vacation driving is done in the mountains of Colorado/Wyoming. Providing that the altitude compensator is in correct working order how effective is it in maintaining good engine performance levels at altitude. I don't expect it to compete with fuel injection but can it make a GW livable in the mountains?
If it isn't worth the effort I would probably look for another 2150 without this feature just to simplify things.

As to the Vapor Canister, my understanding is that the solenoid that controls the connection between the carb float bowl and the canister is only open when the ignition is off and is always closed when the ignition is on?? Yes? If this is correct then doing away with this hose and solenoid should have no effect at all on engine performance, Yes? That would leave the vent in the air horn to equalize pressure and throw off vapor, and since that vent is contained in the air cleaner the flap in the air cleaner that closes after the engine shuts down should mostly contain any evaporative vapors from the carb. Yes?

I would remove the hose and solenoid, cap the nipple on the carb as well as cap the hose barb on the canister. By doing this I would stop any possible debris such as charcoal and rubber bits from finding their way into the float bowl and making my life miserable. Agreed?

For now I would leave the tank vapor hose and purge signal hose alone but if in the future I remove them and cap all vacuum fittings as well as provide a vent for the tank and a vented gas cap I don't see how their removal would effect engine performance. I live in a state with no emission regs nor state inspections so that isn't an issue. My goal is to simplify the snake's nest of hoses and switches and hopefully eliminate future sources of problems Please tell me if I'm wrong in my assumptions
'91 GW
2000 TJ
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Old 07-29-2019, 09:16 PM
acct21's Avatar
acct21 acct21 is offline
327 Rambler
Join Date: May 20, 2014
Location: Austin, TX
Posts: 712
Can't comment specifically on the altitude compensation circuit. Have heard second-hand that they do work at adjusting the mixture at altitude. Guess you will have to try yours and see if it is still functional.

The bowl vent circuit is pretty benign. You're unlikely to ever have anything migrate into the bowl from the vent line. It's pretty effective in keeping fuel vapors contained. Even with the evap flap in the air cleaner closed, it's nowhere near a tight seal. If you keep the Jeep in an enclosed area, you're going to smell gas.

If you're keeping the charcoal canister intact, would certainly consider leaving the bowl vent circuit intact.
1990 Grand Wagoneer with HD towing package -- everything works! (for now...)
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Old 07-30-2019, 08:26 AM
GWJeeper GWJeeper is offline
232 I6
Join Date: Mar 28, 2019
Location: Oklahoma
Posts: 31
The reason I was considering removing the line from the bowl vent to the canister is that I've torn down the carburetor twice in two weeks to find pieces of what appears to be charcoal and deteriorated rubber in the bowl. The last time a piece had clogged one of the primary jets and caused a lot of grief.
'91 GW
2000 TJ
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Old 07-30-2019, 12:47 PM
joe joe is offline
Join Date: Apr 28, 2000
Location: PNWet, USA
Posts: 22,312
Never seen any actual field test data comparing carbs w/ and w/o the barometers usefulness. In theory it should help some but as you mentioned it won't perform the same as a computer controlled EFI system. The mc alt comp unit is just a barometer that when atmospheric pressure drops at elevation it opens up a tiny passage that allows a tiny bit of extra air to lean the mix. Pretty rudimentary system but does help some. "Some" is a relative term as in it helps but is NOT a work around for proper jetting. If yours hasn't been buggered by some previous owner, (not owner adjustable) I personally would not want to lose the barometer. Won't run as well as you hope for at elev but it'll run worse(rich) at elev w/o it. I wouldn't spend money on another carb just to get rid of the alt comp unit. Best thing you can do is keep your motors ignition and carb system tuned to the Nth degree and learn to live with it or rejet and tune for elevation. I used to work in the mountains/Rockies/Cascades in the 70's (geology) and on V8 Chev/Ford/Dodge for short term work I'd advance the ign timing 2* per 1,000ft above 7,000 ft. It helped. If the job was going to be weeks long I'd rejet for the duration and rejet again later bakin civilization.
If you're just hwy traveling through an area and encounter a high pass 7,500+ ft and it's bogging down from running rich you can temporarily remove the air filter element till you crest the summit. No cheap easy bandaids for proper jetting and tune long term
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