Vac Advance Movement
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Vac Advance Movement
78 f150 4X4 351M
I'm getting terrible mileage even with a rebuilt carb (7.7mpg). I'll look at rejetting it soon (due to altitude, we're at 5000' above seal level here) but for now I'm looking at my vac advance. It holds vac if I suck in on the tube and the mechanism inside the body of the distributor is moving (although not by much). My question is how much movement should I expect, and how easy is that mechanism to move normally? Mine doesn't move too much and it takes a LOT of vacuum to get it to pull in. Reaching in and trying to move the mechanism by hand is very hard to do. I went ahead and lubed the mechansim inside the dist but that didn't seem to change anything.
Stan
I'm getting terrible mileage even with a rebuilt carb (7.7mpg). I'll look at rejetting it soon (due to altitude, we're at 5000' above seal level here) but for now I'm looking at my vac advance. It holds vac if I suck in on the tube and the mechanism inside the body of the distributor is moving (although not by much). My question is how much movement should I expect, and how easy is that mechanism to move normally? Mine doesn't move too much and it takes a LOT of vacuum to get it to pull in. Reaching in and trying to move the mechanism by hand is very hard to do. I went ahead and lubed the mechansim inside the dist but that didn't seem to change anything.
Stan
Last edited by 65CJ5; Sep 8, 2004 at 06:03 PM.
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Joined: May 2004
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your vac. adv. is adjustable. get a 1/8 allen wrench an stick it in where the vac. hose goes into the vac. adv. unit on the dist.(remove the hose first
)
turn the wrench until it engages the screw, then turn the screw clockwise counting the turns until it stops, try it there and drive it a bit, if it pings, turn it back half the turns you did before and drive it, you'll find the right balance.
btw, if you have factory a/c, then you'll have to make an allen wrench to fit(bend it!) good luck!
)turn the wrench until it engages the screw, then turn the screw clockwise counting the turns until it stops, try it there and drive it a bit, if it pings, turn it back half the turns you did before and drive it, you'll find the right balance.
btw, if you have factory a/c, then you'll have to make an allen wrench to fit(bend it!) good luck!
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Matt, thanks for the info. I will try adjusting it and see what it does. It runs OK but not as good as I think it should. I am starting to suspect something with the timing now in terms of the ultra-bad mileage I'm getting. I also think an engine this honking big should have more power than it does too. Again, may be timing issues.
Stan
Stan
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Joined: Nov 2000
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From: Albuquerque
You will only see a little movement in the vacuum advance from sucking on it. A mitivac is good for checking it as you can observe with a timing light while you apply a higher vacuum and determine the total vacuum advance movement. I wouldn't mess with adjusting it other wise as you can't tell what you are doing. At your altitude you can probably benefit from smaller carb jets ( a size or two) and a little more intial timing.
they just arent take off machines.
