altitude compensator valve
10-05-17, 04:39 PM
#1
Rotary Noob
Thread Starter
altitude compensator valve
Has anyone replaced an Altitude Compensator Valve on an FB? My '82 GSL stumbles and hesitates to get going so I was going to replace the valve before messing with the Holley it has and or taking the car in somewhere. I found a service bulletin from 1985 on ALLDATA describing symptoms of a faulty Altitude Compensator Valve and they matched the problems I'm having with my car. Thoughts anyone?
10-06-17, 01:25 PM
#2
It sounds to me like something else is up with your carb. I remove the alt comps on the carbs I "hot rod" to handle boost and NA, so I know all about how these carbs run with that thing removed (hint: they run really well!).
You probably have an old hard accel pump diaphragm and maybe some small vacuum leaks that all lead to a mildly lean condition which you are attributing to a faulty alt comp. The mixture screw, which was hidden under a metal cap on all 81-85 carbs, could probably use an adjustment after 30-some years. The throttle shaft and bushing have been wearing slightly letting in more air than it did when new. The mixture screw needs to be turned out a little to account for the extra air.
You see, it's all the little things that add up to a bigger problem which you have probably masked by adjusting the throttle stop (speed) screw as that is the only one accessible on a stock carb.
You also have a pretty weak ignition system which could be helped by a direct fire upgrade. It makes these engines run really well compared with weak factory ignition.
Edit for additional info: if you get a carb rebuild kit, DO NOT replace the factory needles and seats with the ones in the kit. They are incorrectly machined for these carbs and lead to instant flooding.
You probably have an old hard accel pump diaphragm and maybe some small vacuum leaks that all lead to a mildly lean condition which you are attributing to a faulty alt comp. The mixture screw, which was hidden under a metal cap on all 81-85 carbs, could probably use an adjustment after 30-some years. The throttle shaft and bushing have been wearing slightly letting in more air than it did when new. The mixture screw needs to be turned out a little to account for the extra air.
You see, it's all the little things that add up to a bigger problem which you have probably masked by adjusting the throttle stop (speed) screw as that is the only one accessible on a stock carb.
You also have a pretty weak ignition system which could be helped by a direct fire upgrade. It makes these engines run really well compared with weak factory ignition.
Edit for additional info: if you get a carb rebuild kit, DO NOT replace the factory needles and seats with the ones in the kit. They are incorrectly machined for these carbs and lead to instant flooding.
10-06-17, 02:52 PM
#3
Rotary Noob
Thread Starter
It sounds to me like something else is up with your carb. I remove the alt comps on the carbs I "hot rod" to handle boost and NA, so I know all about how these carbs run with that thing removed (hint: they run really well!).
You probably have an old hard accel pump diaphragm and maybe some small vacuum leaks that all lead to a mildly lean condition which you are attributing to a faulty alt comp. The mixture screw, which was hidden under a metal cap on all 81-85 carbs, could probably use an adjustment after 30-some years. The throttle shaft and bushing have been wearing slightly letting in more air than it did when new. The mixture screw needs to be turned out a little to account for the extra air.
You see, it's all the little things that add up to a bigger problem which you have probably masked by adjusting the throttle stop (speed) screw as that is the only one accessible on a stock carb.
You also have a pretty weak ignition system which could be helped by a direct fire upgrade. It makes these engines run really well compared with weak factory ignition.
Edit for additional info: if you get a carb rebuild kit, DO NOT replace the factory needles and seats with the ones in the kit. They are incorrectly machined for these carbs and lead to instant flooding.
You probably have an old hard accel pump diaphragm and maybe some small vacuum leaks that all lead to a mildly lean condition which you are attributing to a faulty alt comp. The mixture screw, which was hidden under a metal cap on all 81-85 carbs, could probably use an adjustment after 30-some years. The throttle shaft and bushing have been wearing slightly letting in more air than it did when new. The mixture screw needs to be turned out a little to account for the extra air.
You see, it's all the little things that add up to a bigger problem which you have probably masked by adjusting the throttle stop (speed) screw as that is the only one accessible on a stock carb.
You also have a pretty weak ignition system which could be helped by a direct fire upgrade. It makes these engines run really well compared with weak factory ignition.
Edit for additional info: if you get a carb rebuild kit, DO NOT replace the factory needles and seats with the ones in the kit. They are incorrectly machined for these carbs and lead to instant flooding.
10-06-17, 03:03 PM
#4
Rotary Noob
Thread Starter
Just as reference this is what the seller said exactly about the car "The car is currently not running that great. Was doing some carb work to correct a lean stumble when accelerating, and ended up causing it to run worse. Will idle OK but when under load just off idle it stumbles badly until really getting into it. Possibly have a Holley power valve problem in the carb, or some other issue with the idle air bleeds, as that is what we were working on at the time. Jetting is not too bad and the float bowl levels and idle pump have been set correctly, so not sure what is causing the issue. I don't have time right now to work on it so the car is sold as-is and will need some work. Would be best to tow it home."