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Benson · 06-09-2015, 08:48 AM

SAJ,

Are you running a fuel pump with this engine setup?

From your post #18 above I can say most likely that you are not using a fuel pump.

I have been using B carbs on A and B engines for 50 years.

I always had lean mixture problems with them Using the:

1. "head with a large B" (Most use is with this head starting in 1963.)

2. 6.5 Lion head,

3. Thomas 8.5

4. stock heads.

I finally stopped using B Carbs for a long time.

I had to run the GAV at 1/2 to 2/3 or more but it still had all the signs of being a lean mixture which my Exhaust Gas Analyzer confirmed.

Then some years ago I found an answer to the problem.

Here is an Ahooga post from 2010 of what I found:

Benson

08-08-2010 08:28 AM

Does your Model B carb-run bad with GAV closed?

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 to 2/3 turn open). Low power, little torque, surging under light loads and running hot around town. At higher speeds and WOT it gets worse. All jets were replaced with a set of flow tested jets from Runner's Corner. Passages checked etc.

I tried several B carbs with same result.

Here is how I fixed it.

A little history first. When the Model A went out of production Ford or Zenith (not sure which) released a second version of the Zenith B 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.

1. 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 to control fuel surges).

2. 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. Low end torque is much better, surging is gone and the car will now go 65-70 MPH with ease.

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 think the ball may be too small and might slip through the enlarged hole!

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 drill press you will strike the needle valve with the flutes on the rotating bit, catch the needle and damaged it.

Note I have not tried drilling out a #44 as I have found a couple of #55’s. Maybe the needle will drop down through the seat hole after drilling

Note: I found some inlets stamped 44 and one 55 (that 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.

MikeK

08-08-2010 09:01 AM

Re: Does your Model B carb-run bad with GAV closed?

Benson, good info! Perhaps the Zenith A carbs could benefit from enlarging the meager pin-seat hole in their float valves too. Now I have to go find one and play with it.

end MikeK comments

SAJ:

In post #13 you mention that you found NO change in EGT when opening up the GAV.

1. I believe that this is because the fuel level in the float bowl is not being maintaned due to the restricted Float valve inlet. I found similar problems also in the past.

2. Another B carb problem caused by the failure to maintain Float level is that when the Power Jet function kicks in at about 75% throttle under high engine loads, the float level is lowered even more by the demand for more fuel. At the same time the fuel level in the main and cap jets is lowered. This makes for even leaner mixture and all of the problems that go with it.

There are few B carbs with the #55 inlets because these were only supplied on the Zenith after production B carbs.

06-09-2015, 08:48 AM	#22
Benson Senior Member Join Date: May 2010 Posts: 2,613	Re: Cracked babbitt SAJ, Are you running a fuel pump with this engine setup? From your post #18 above I can say most likely that you are not using a fuel pump. I have been using B carbs on A and B engines for 50 years. I always had lean mixture problems with them Using the: 1. "head with a large B" (Most use is with this head starting in 1963.) 2. 6.5 Lion head, 3. Thomas 8.5 4. stock heads. I finally stopped using B Carbs for a long time. I had to run the GAV at 1/2 to 2/3 or more but it still had all the signs of being a lean mixture which my Exhaust Gas Analyzer confirmed. Then some years ago I found an answer to the problem. Here is an Ahooga post from 2010 of what I found: Benson 08-08-2010 08:28 AM Does your Model B carb-run bad with GAV closed? 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 to 2/3 turn open). Low power, little torque, surging under light loads and running hot around town. At higher speeds and WOT it gets worse. All jets were replaced with a set of flow tested jets from Runner's Corner. Passages checked etc. I tried several B carbs with same result. Here is how I fixed it. A little history first. When the Model A went out of production Ford or Zenith (not sure which) released a second version of the Zenith B 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. 1. 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 to control fuel surges). 2. 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. Low end torque is much better, surging is gone and the car will now go 65-70 MPH with ease. 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 think the ball may be too small and might slip through the enlarged hole! 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 drill press you will strike the needle valve with the flutes on the rotating bit, catch the needle and damaged it. Note I have not tried drilling out a #44 as I have found a couple of #55’s. Maybe the needle will drop down through the seat hole after drilling Note: I found some inlets stamped 44 and one 55 (that 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. MikeK 08-08-2010 09:01 AM Re: Does your Model B carb-run bad with GAV closed? Benson, good info! Perhaps the Zenith A carbs could benefit from enlarging the meager pin-seat hole in their float valves too. Now I have to go find one and play with it. end MikeK comments SAJ: In post #13 you mention that you found NO change in EGT when opening up the GAV. 1. I believe that this is because the fuel level in the float bowl is not being maintaned due to the restricted Float valve inlet. I found similar problems also in the past. 2. Another B carb problem caused by the failure to maintain Float level is that when the Power Jet function kicks in at about 75% throttle under high engine loads, the float level is lowered even more by the demand for more fuel. At the same time the fuel level in the main and cap jets is lowered. This makes for even leaner mixture and all of the problems that go with it. There are few B carbs with the #55 inlets because these were only supplied on the Zenith after production B carbs. Last edited by Benson; 06-09-2015 at 12:06 PM. Reason: Several corrections and additions since first posted