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I've got my engine back in and I re-installed my Carter/Webers on a 2x Offy intake. It seems like they are still running rich. I put a vacuum guage on the intake and it's drawing 15-16" of vacuum. I can't seem to find an air/fuel mixture valve to adjust. Can someone send me instructions for setting these carbs? Thanks.

Jerry I don't think there is an idle mixture screw on these. I'm told you have to change the jets and (?) rods?? I'm not even sure it has rods.

Needless to say I'm unsure too so hopefully Carbking will set us straight.

I got a set of those from Langdon's.

They are Motorcraft Model 740 2 barrel carbs.

If you turn the carb so that you are looking at the side with the accelrator pump and three vaccum fittings (the choke should be on your right and fuel inlet on the left), the mixture screw is at the bottom center of the mainbody. From the factory there is a plug in the little tube enclosing the mixture screw that you'll have to remove to be able to make adjustments. In the image below the idle mixture screw is # 60 and the cap/plug is number 63/58/59.

Regarding jets, the instructions from Langdon say:

"Jets may be changed by remvoing the aircleaner mounting bridge (not numbered) and using a very tight fitting screwdriver in the top of the jet holders. These are very tight, so heavy down force should be applied while turning the screwdriver to avoid damage to the slot."

From the diagram that came with the carbs from Langdon, the idle jet holder screws are numbers 38 and 43, the idle jets are numbers 39 and 44. The main jets screws are numbers 40 and 45(aka air bleeds), the main jets are 41 and 46 (at the end of the well tubes).


[img]http://www.carburetorfactory.com/images/expvw09.jpg[/img]

Thanks. That's where they were. It didn't even have the caps on it. I hadn't paid any attention to that hole because it's so small. Interesting thing is that when I started, I had 16" of vacuum. I turned those screws in until the engine started to stumble and back out until it stumbled on the other end. There was very little vacuum variation. Problem? (I'm drawing my vacuum off the Offy intake.) I set both carbs to the middle point between those points.

There are 3 places to draw vacuum; two on the carb and on in the center of the intake. There are two points about a third of the way up from the bottom on each carb. The other is at the very base of the carb. Where should I draw vacuum to adjust the carb? Where should I draw vacuum to drive the vacuum advance?

There are two places to draw vacuum for the distributor-

Off the manifold directly- That is "unported"

Off the carb- ported. the vacuum fitting reccomended by Langdon on the Motorcraft 740 (Carter Webber) is the one on the right of the mixture screw and above it. It is directy to the right of the where the idle shutoff solenoid (#11) would be, but is plugged for use on these trucks.

Langdon's instructions are to try both ported and unported to see which one works better.

Thanks NM51. If I'm facing the air mix screw hold, there's a vacuum line directly to the left and two above it. It sounds like I want to use the right one of the two above the mixing screw. Right?

Yup, thats the one.

Carb King can probably tell us how to find different sized jets for this carb if you decide to go that route.

While we are on the subject of this carb, don't forget to plumb a pressure regulator into the fuel line between the pump and the carbs. These carbs need about 3.5 and those mechanical pumps can put out more than that at higher rpms. before I put a pressure regulator in my carbs would flood because the high pressure would jam open the needle and seat valve. If that happens you can just tap on the air horn above the needle and seat valve, and that should unstick it. However, that little maneuver is tough to do at 75 mph on the freeway!

Holley make a non-chrome low pressure fuel regulator that isn't that noticble. You can also get generic adjustable chrome/anodize aluminum pressure regulators at NAPA or your local FLAPS. There are high pressure and low pressure so make sure the one you buy will adjust down to 3.5. The higher pressure ones don't go that low 'cause they're made for fuel injection systems.

This thing seems awfully rich. I ran the air/fuel screw in until the engine stumbled and then back out until it stumbled again. There was very little difference in the vacuum reading off the intake. In fact, it was only about an inch. I currently have both carbs set for the max vacuum which is about mid point. Like I said, she sure smells rich.

What are your thoughts?