Lynn;  As mine is lying on the bench, I looked in and it has 42's.  JohnD

If Ken has 37MM venturies, his 200 mains will be on the rich side all through the RPM range.

However, he injects nitrous for takeoff and may inject some additional fuel along with it.

So richer is not hurting anything.

 

The main jet controls all fuel entering from the float bowl. So, a change in main jet size changes everything from idle to top RPM. The emulsion tube takes air in through the air corrector jet and mixes it with fuel coming in through the main jet. How deep below the float bowl fuel level air is mixed with the fuel determines intermediate RPM performance. Lower holes make the fuel column lighter, and it will lift faster and flow out into the auxiliary venturi.

(the big tube sticking out the center of the bore).

 

The 42 MM venturies are about as big as you can go and still have any off idle performance.

In other words, the venturi size controls how much vacuum will be available to draw mixture out of the lower end of the auxiliary venturi. The vacuum is called signal in carb talk.

Smaller venturi = better signal. Bigger venturi=Worse signal.

 

Once the engine is spooled up, none of this matters. Cruise RPM will just involve the air corrector, the emulsion tube and the main jet.

 

The two big hollow screws between the bores are hold down screws. Use a big bladed driver to take them out. Pressed into the bottom of that screw is the emulsion tube. Hold onto the hold down screw and pull hard on the emulsion tube. (The brass tube with all of the holes).

 

The screw comes off, and now you see the air corrector pressed into the top of the tube, and the main jet pressed into the bottom of the tube.

 

There you are. That is the whole cruise fuel control system.

 

A change of one main jet size is the same as two air corrector sizes. The F-7 emulsion tube is in the middle of the mixture range.

 

The tubes and jets have the sizes (in MMs) stamped into them.  

 

Take the needle seat out and if that little screen is still in there, throw it away. The land area it sits on may be drilled out to 1/4" lest it be the main jet.

 

I think you will like the carb. Not fussy at all.

 

There is a gag for mixture control on the dyno, so you don't have to stop and change jets, and it involves making a cover for the well where the two sets of hold down screws live.

The smaller ones are the idle jet holders. So you make a tall cover that can seal off this area.

Install a 1/4" piece of brass tubing. Another piece of tubing stuck into the intake manifold.

 

run them onto a "T" from the fish tank supply house. Install a needle valve in the run to the intake and one in the leg of the Tee. Now you can change mixture with the engine screaming. The more vacuum exposed to the air correctors the richer it runs. So you start off lean and control EGT with one of the needle valves. No rules about a needle valve on the dash board.

 

As you go up, you adjust for more air and less vacuum. The engine leans out.  

 

Lynn E. Hanover