Original 4bbl carb tuning

[Dogster]

Anybody out there remember how many turns out the mixture screws were set on the 85 4 bbl? Need a good starting point and I know the mixture screws were originally sealed in a plastic so they couldn't be tampered with. I just can't recall how many turns out they were set...

[grabbergreen84]

You should use the standard 1.5 turns-and-go-from-there method.

[bwguardian]

The mixture screws...all four of them...are sealed off by a metal cap insert which can be removed. As stated above, I would start with snugging them down then turn them back out 1.5 turns and start with that.

[mustangxtreme]

Snugging them down may have different meanings to different people. For me when I adjust mixture screws, I will gently turn them down until they seat and no more. This keeps the needle & seats from being damaged and ensures you will be able to get a good adjustment.

[Dogster]

Thanks. I was thinking it was 2 1/2 turns but I'll start at the 1 1/2 starting with snugging the screw down gently. Carb shop I took the carb to for a stuck mixture screw went to drill the screw out and accidentally went through the baseplate. They replaced the baseplate and set the mixture screws 3 turns out. Way too rich. Unfortunately the new baseplate is off a Ford truck so it's s little different on the secondary side. Now does anybody have an easy method to adjust the screws without taking the carb off each time to turn the screw? I still have the EGR plate and heat shield on mine so there's little clearance - and tough to tell if you're on the screw correctly or not and if you're actually turning it when everything is bolted down tight.

[JACook]

If they replaced your baseplate with one that does not have the rear screws, I would insist they find another.
Some truck baseplates did have the secondary mixture screws, some did not.

Also, make sure they kept the Mustang primary throttle shaft, else the WOT switch will not work. Mustang
4180Cs were the only ones that had the tab on the primary throttle arm.

[jessesandy]

How many turns to back off as a starting point isn't too important. When you turn them in to adjust, keep going to all four corners and keep turning them in. When you think they are in too far they can probably go in farther. (SMOG in California pisses me off).

PS: were you talking about the "factory Holey" (make that Holley)

Thanks, Jesse

[jessesandy]

I use a "Torx driver". Its like a nut driver (or a screw driver) for Torx head screws. Since the Torx is like a 6 pointed star so it will fit into an allen type screw.

[83gtstang]

Try to get a vacuum gauge. Run the car and adjust idle air fuel mixture until you get the highest vacuum reading. Once you get the highest vacuum reading, divide the reading by two. That number will be the size of the power valve you will need if after adjustment your car still smells rich.

[JACook]

To clarify this a bit, an incorrect power valve can cause either a part-throttle lean condition, or a part-throttle
rich condition, depending on which way it's wrong. The rating of the power valve has nothing to do with idle
mixture. If the power valve ever affects idle mixture, it's leaking, or it's gasket is leaking.

I generally use a ball-tip Allen wrench to adjust the idle mix screws. But you may have to tweak the heat
shield a bit to get to the rear screws. Or get a flexible idle mixture screwdriver that has a 3/32" bit, like this
one - http://www.ebay.com/itm/AMPRO-T71301...-/331440368595

[83gtstang]

Sorry I didn't go into much explanation, it was late. Reading now, that I read what I wrote, I mixed two different explanations without explaining what I was trying to say. Idle air mixture is one thing. Power valve is the other.