air mixture screws

[berg bronco]

what is the proper way to adjust the air mixture screws on a 2v motorcraft 2150 carb?
ive heard adjust them in until it runs rough and then back out a 1/4?
but i cant seem to get it right? any help is appreciated!

 

[oleguy74]

turn in til they stop,then out 1 1/2 to 2 1/2 turns.this is average.don't turn in tight as you will damage the seat.

 

[gladkin]

Best way is to get a vaccuum gauge. You want to see around 20-25 psi of vacuum pressure when at idle. Put the vacuum gauge on your vacuum advance tube and then adjust one idle set screw until you get max vacuum pressure and the pressure stops increasing on the gauge. Then perform the same operation using the other idle set screw. Switch between idle set screws until everything is equalized and the pressure sits right.

Typically this is around 2.5 turns. At 1.5 turns you will most likely run lean and this could cause damage over time as you will torch out your exhaust valve seats if you run too lean.

Note on Dwell/Tack for your distributor. Lookup what your distributor requires if you are running points. As I recall, manual trans requires 27degrees of dwell, auto trans requires distributor dwell at 29degrees, but make sure from manual. Dwell/Tack is the most important part of timing to ensure that you get proper fuel burn. Without proper fuel burn, all the idle adjustment in the world will still cause your engine to run improperly.

Hope this helps!

Michael

 

[berg bronco]

thanks,that helps alot!

 

[broncnaz]

I usually start 2 turns out then once the vehicle is fully up to temp adjust until the idle gets better or worse then turn the other way until it starts to stumble again then adjust to your liking between those 2 points a vacuum gauge helps but dont worry about actual PSI. as not all engines will pull 20 or more PSUI at idle, Just adjust for the highest steady reading you can get.
Also make sure your timing is set before you play with the carb as changes in timing may require changes in idle mixture.

 

[bknbronco]

i can turn my screws in and out and nothing ever changes. Carb had just been rebuilt. It runs fine so i left it. Just wanted to point that out because if your having similar problems your just spinning your wheels.

 

[KUBOTA OWNER]

The best way that I learned while working on all the old fords was to do a (lean drop adjustment). --Hook up a good tach and adjust the base idle speed
as close as possible. Now turn one mixture screw out 3 or four turns and then start slowly screwing it back in until you notice a slight drop in rpm's. Now go to the other screw and do the same. (remember to adjust your base idle as needed). Now go back to the other screw and adjust it slighty open again until the rpm pick up, then start leaning it out again watching the rpm's. now go back to the other screw and do the same again. --- This will give you the best idle quality and fuel economy.

 

[broncnaz]

If you dont get any changes while adjusting the screws then something is wrong somewhere. could be a vacuum leak, Idle speed set to high or other issue. yes the engine wican still run fine you may not be using the idle circuit.

Idle mixture screws have nothing to do with fuel economy. Unless you just idle around all the time.