This was discussed last month on FB so it may be of interest to some.
I have had trouble for a long time with a B carb on my Model B engine that will not run right with the GAV closed .
It must be 1/2 to 2/3 turn open (it is better but still not right with GAV 1/2 turn open). Low power, little torque, surging under light loads and running hot around town. At high speeds and WOT it gets worse. All jets were replaced with a set of flow tested jets from Renner's Corner. Passages checked etc.
Here is how I fixed it. A little history first. When the Model A went out of production Ford released a second version of the Zenith B2 Model B carb for replacement use with the Model A. It had a #20 venturi vs #22 for B, several jets are smaller and most important they changed the fuel inlet (needle valve assy) from #44 to #55.
The 44 was for the Model B which has a fuel pump (note: Float spring must also be used in B carb if you have a fuel pump).
The 55 was for the Model A which as you know has no fuel pump.
The 44 has an .082 inch inlet hole.
The 55 has a .110 inch inlet hole.
Do the math: (Pii R squared) and you will find that the .110 has twice the area on the inlet hole, so it allows twice the gasoline to enter the float bowl when you are not using a fuel pump, the pressure with the pump allows enough gas through the 44 inlet and the float spring helps to prevent the pressure from overloading the float and flooding the float bowl).
It is amazing how much better the car runs with the 55 inlet valve (I do not run a fuel pump) with my B carb. Lowend torque is much better, surging is gone and the car will now go 65-70 MPH with ease. Mine has some goodies.
Try it you will like it.
I had trouble finding the 55 inlets so I drilled out a 44. (.110 or #35 drill bit as I remember) The #45 drill is .082 and can be used to check the size on the 44 inlet.
Note: I do not know how drilling will work on the "Grosejet" inlet assemblies (the ones with the 2 balls instead of needle jet). I looked at several and was not sure that the ball would drop down far enough to allow drilling all of the brass out of the hole. Maybe you could take the balls out, drill and then replace them.
If you are drilling out a #44 I suggest that you use a drill press and set the bottom stop JUST above the steel needle valve THEN drill it out. If you do not use the stop on the drillpress you will strike the needle valve with the flutes on the rotating bit, catch the needle and damaged it.
Note: I found some inlets stamped 44 and one 55 I borrowed from a friend stamped 55. Some of the 44s were stamped with just 4 so you might find a 55 stamped with just 5.
I have had trouble for a long time with a B carb on my Model B engine that will not run right with the GAV closed .
It must be 1/2 to 2/3 turn open (it is better but still not right with GAV 1/2 turn open). Low power, little torque, surging under light loads and running hot around town. At high speeds and WOT it gets worse. All jets were replaced with a set of flow tested jets from Renner's Corner. Passages checked etc.
Here is how I fixed it. A little history first. When the Model A went out of production Ford released a second version of the Zenith B2 Model B carb for replacement use with the Model A. It had a #20 venturi vs #22 for B, several jets are smaller and most important they changed the fuel inlet (needle valve assy) from #44 to #55.
The 44 was for the Model B which has a fuel pump (note: Float spring must also be used in B carb if you have a fuel pump).
The 55 was for the Model A which as you know has no fuel pump.
The 44 has an .082 inch inlet hole.
The 55 has a .110 inch inlet hole.
Do the math: (Pii R squared) and you will find that the .110 has twice the area on the inlet hole, so it allows twice the gasoline to enter the float bowl when you are not using a fuel pump, the pressure with the pump allows enough gas through the 44 inlet and the float spring helps to prevent the pressure from overloading the float and flooding the float bowl).
It is amazing how much better the car runs with the 55 inlet valve (I do not run a fuel pump) with my B carb. Lowend torque is much better, surging is gone and the car will now go 65-70 MPH with ease. Mine has some goodies.
Try it you will like it.
I had trouble finding the 55 inlets so I drilled out a 44. (.110 or #35 drill bit as I remember) The #45 drill is .082 and can be used to check the size on the 44 inlet.
Note: I do not know how drilling will work on the "Grosejet" inlet assemblies (the ones with the 2 balls instead of needle jet). I looked at several and was not sure that the ball would drop down far enough to allow drilling all of the brass out of the hole. Maybe you could take the balls out, drill and then replace them.
If you are drilling out a #44 I suggest that you use a drill press and set the bottom stop JUST above the steel needle valve THEN drill it out. If you do not use the stop on the drillpress you will strike the needle valve with the flutes on the rotating bit, catch the needle and damaged it.
Note: I found some inlets stamped 44 and one 55 I borrowed from a friend stamped 55. Some of the 44s were stamped with just 4 so you might find a 55 stamped with just 5.
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