Model B Carb issues

KMeredith87

KMeredith87

Senior Member
I have two model B carbs that's I have recently rebuilt but don't run. The castings were thoroughly cleaned out and inspected prior to painting. One has an original numbered set of jets while the other has a flow checked set from renners in it. Both seam to seal fine and don't leak fuel but won't run. The truck runs fantastic and starts with no issues with my zenith 1 on it. This is my first experience with model B carbs and am not sure what's up. Any thoughts? I'm a bit stumped...
 
Definitely getting fuel. Sometimes they will start but won't stay running but most of the time they won't even start
 
Sounds like a either a fuel starvation or vacuum/blockage of some kind. They are not much more complicated than an A carb. I would tear it apart and make sure every passage way is clean, the fuel screen is clean, jets and reassemble.

Mike
 
If you didn't drill out the plugs and clean the "hidden" passageways, the carb was not truly rebuilt. The most likely culprit is in the upper casting near the idle richness needle. Drill that passage out, if you do no others. That's the one most prone to clog up. A clogged passageway here will definitely make starting and idling difficult, if not impossible, depending upon on how clogged the passageway is.
Marshall
 
Just original manifolds installed, both intake and exhaust. However, the intake has been bored out to model B dimensions.

As for the brass plug passages I have not seen replacement plugs for the model B carb so I cannot drill them out... I have gone through them with a fine wire like you would a model a zenith 1 and have found them all clear and also was able to flow wd40 through them...I know that may not mean they're completely clear but best I can do with out having new plugs...

Just opened them back up and did not find anything g out of the ordinary inside. And there is not screen like the A carb so no issue there. I also have good flow coming from the tank. Not sure what's going on but I know it's frustrating!!
 
There is a removable brass plug in the upper housing that has a vertical slit in it that is open to the throat of the carburetor. Careful tap it inward until it falls out and check the top of the idle passage under this plug for rust and dirt. Also, under the GAV is prone to rust also and the GAV is pressed into the lower body of the carburetor. If you haven't removed to GAV totally, the engine will never run right.
 
I was about to ask the question about the model B carb myself,I had taken a few trucks to Brooks Oregon over the weekend for the show there and in the load I took was a 1932 canopy express truck,I ended up using it for wheels to and from the motel and noticed that the carb had a cable for a choke but on inspection of the carb it looks like a GAV on it but its operated by a choke cable just to pull the choke on is that all there is on these or are they adjustable like the A's.
 
ABento said:
I was about to ask the question about the model B carb myself,I had taken a few trucks to Brooks Oregon over the weekend for the show there and in the load I took was a 1932 canopy express truck,I ended up using it for wheels to and from the motel and noticed that the carb had a cable for a choke but on inspection of the carb it looks like a GAV on it but its operated by a choke cable just to pull the choke on is that all there is on these or are they adjustable like the A's.
Click to expand...

B carbs are normally set up just like A carbs, and have the same choke and GAV controls.
 
No worries Sparky not no I did not forget them. Both carbs have an original proper sized venturi in them.

AL...didn't realize I could tap that plug out, I'll give it a shot and see what I get. However, one of my carbs is actually an early casting that does not have that plug only drilled like a model a zenith...
 
Naive question and slightly off topic - is there an advantage to running a model B carb versus a Zenith-1 ?
 
Yes there is a slight advantage . The B carbs have a larger throat and more venturi area and a high speed circuit that cuts in at near wide open throttle. They also flow more air than any of the updraft carburetors that are commonly used on model A and B engines.
 
Right where your power jet tube goes in is a very tiny vent hole goes in on a angle . make sure it is open.
 
Okay so here is an update...took them apart today and as suggested I knocked out the split brass plug and cleaned it out, rechecked the passages and reassembled. Put it on the truck and was able to get it to run and idle smooth. Everything seemed fine would Rev the engine no problems things looked good until I tried to drive it. Made it about 50 feet and it died and did not want to start again. Put the zenith one on to get it back inside, no problems...the mystery continues...
 
Do you still have the float helper spring installed, if so maybe
that is part of the problem.

Bob
 
I'm no expert, but I also have two B carbs, one of which I am currently running on my speedster. The first one I got ran great, I didn't need to do anything to it other than replace the gaskets. I was able to get the second one at a great price, and although it looked very nice, it ran like crap; the engine started but wouldn't idle and did not accelerate smoothly. When I carefully compared it to my original good one, I found two problems:

1. The compensator jet was not marked, and although it appeared to be the correct drill size, it was actually a jet meant for the Zenith A. The difference is that the correct B jet is shorter in length. So I got an original B jet (marked "18") and that fixed the acceleration issue.

2. The idle air screw had no affect on the idle even when completely closed. I found that the screw threads were either rusted or dirty near the bottom of the hole so the needle was not fully seating even though the screw stopped turning. Chasing the threads with a jet tap fixed that issue.

Also, neither of my carbs have a float return spring.

Other than the "power valve" circuit they work just the same as the Zenith A. One thing you could experiment with is swapping the tops and bottoms.
 
I'll give it a shot swapping bottoms out as the one has all original jets while the other has flowed jets from renners (I've heard nothing but good things about them, no complaints here but who knows). I get adjustment from my air mixture screw so no problems there. I actually had it running great until I tried to drive it off...
 
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