Carburetor

[darren]

Since you mentioned you had the carb rebuilt ...Did they set the float to factory specs. if  they did you could be dumping a lot of gas down the manifold!.. Todays gas is not the same as in the day.. Have someone or yourself lower the float a bit .  BEST way to do this is before and after test using a 4 GAS ANALYZER..  Made a BIG differance for me . Happy Plymouthing DANiel

[FourDoor]

Just putting in my 2 cents worth because it's already been said, but the only way to adjust the air bleed screw is with a vacuum gauge. Hook it up where the windshield wiper line is on the side of the intake manifold. Disconnect the wiper line and connect up the vacuum gauge. Turn the idle screw in to speed up the engine to about 750 to 1000 rpm. If you don't have a tach just adjust the idle a little higher than you would want it normally. Then adjust the air mixture screw for the highest vacuum. This is the ONLY way it should be adjusted. Then turn the idle down to a speed that will not let the engine stumble if you let out the clutch in 1st gear with your foot off the gas pedal. This makes it easy to run in parades. Adjusting the air mixture screw with the visibility a vaccum gauge gives you, gives you the confidence to move on to other areas if gas mileage is still a problem. And don't forget to take the 'accelerator pump' down to it's last notch. You only need a small injection of gas during gear shifts to prevent stumbling or to prevent stumbling at move off. The other notches are for winter starting and driving and you don't need them in the summer.? ? ?

[plym_46]

What measure are using to determie too much.? Is your expectation to high??? What level of fuel consumption are you expecting.

What objective measurements have you made?? What are your cylinder compression readings, how many inches of vacuum does your engine develop? What do the spark plugs look like after 100 miles,? ?Are they correct, are they gapped correctly?? Are your points set correctly, is your timing correct, if you have vacuum advance is it working properly?? If you have mechanical ignition advance are you adjustig it properly for operation?? How are you driving your car??

Your carburetor is a preset analog device.? Assuming it is in good mechanical condition, the amount of air passing throug it determies the amount of fuel it will draw through and into the engine.? There are two exceptions to this, the accelorator pump, the linkage may be adjustable for length and therefor determine the amount fo fuel pumped per stroke.? The onter is internal and is the step up por power circuit internal to the carb.? This is cotrolled by manifold vacuum and there is a passage from the intake through the carburetor.? If this passage is blocked (the common cause is improper inatallation of the carburetor to manifold gasket) he power valve will be open all the time.? This will lead to rich operation and excessive fuel cosumption.? The vacuum passage keeps acts on a piston that holds a needle valve into the enrichment jet.? As you step on the gas pedal, intke manifold drops, the spring in the circuit over comes the weakened vacuum signal and puls the needle out of its jet, enrichining the fuel mixture.? As vacuum is restored, it pulls the needle back into the seat, closing the valve.? So minus a proper vacuum signal, this jet will be open at all times.?

There is a slot in cut into the gasket that is supposed to allign with a port int he base of the carburetor, to allow the vaccum signal to be applied to the piston.? Assure the gasket is alligned to allow vacuum into the carb.

I have an aquaintance who installed his gasket incorrectly.? This in a 54 Plymouth.? With Od trrans it would get about 14 miles per gallon, and the plugs while not fouled, were sooted as a result.? With the change in gasket alignement, fuel mileage increased by aproximately 3 to 4 mpg in open road driving.

The external adjustment screws ffect nothing but the engines idle circuit.? This circuit is bypassed when the throttle plate is opened past the idle ajustment.

I have a 46 business coupe, when I got it it had the stock 218 engine, with the 4.11 rear end it would get about 17 mpg.? I have installed a later 230 engine, with milled head and block, dual carburetors, and taller rear tires.? Currently it gets just over 19 miles per gallon.? What is your expectation?

Your question regarding adjustment of the idle screws accordint to the manual is;  Adjust the timing to the correct setting at idle.  Then adjust the idle speed on the engine warmed to operating temp to obtain an idle speed of 450 to 500 rpm, then adjust air bleed screw to obtain the smoothest idle.  Then recheck the timing.  If you do not have a timing light, do a proper tdc static timing setting, and then adjust to obtain the highest vacuum reading at idle.

[36 Ply]

Hi Jean,

I probably have the procedure for adjusting the carburetor in one of my manuals, which are out in the detached garage. If no one replies to your post soon, I'll see if I can find them, as I haven't adjusted a carburetor in a long time.

In the meantime (please don't get upset if you've already thought of this) there could be other reasons for your gas consumption, such as:

Dragging brake(s)                  Float level too high                                                  Spark timing off
Tire inflation                          High fuel pump pressure (this one happened to me)    Bad plug wires
Extra weight in trunk              Leaking fuel pump diaphragm                                    Spark plugs dirty
Dirty air cleaner                      Leak in gas tank or lines                                            Spark plugs gapped too wide
Defective condenser               Weak coil                                                                Worn breaker points
Manifold heat riser problem       Leak in wiper hose                                                    Intake manifold gasket leak

There are other conditions that affect gas mileage, these are some of the most common ones.

Regards,

Pat O'Connor

[my33ply]

If you have the same carb as me, the idle screw is just that. It moves the throttle in or out to feed more fuel. The adjustment screw is best handled with a vacuum gauge. Adjust until you get the highest vacuum and then use the other screw for desirable rpm's.

[Jean]

Need to adjust the carburetor. The ply is burning to much gas. Carburetor was rebuilt. There are two screws: one is the idle adjustment screw. the other screw (i assume) is to adjust the air/gas mixture too. If you turn the screws counter clockwise the engine slows or drops. And of course turning the screws clockwise increases the engine. What is the turn ratio for each screw? For example, if I turn the idle screw 1/2 turn, then do i turn the air/gas screw a whole turn?

Jean
'41 ply special deluxe 4- door