Model B carb dying at stops

M

mcgarrett

Well-known member
I am running a Model B carb and intake on my newly rebuilt Model A engine and everything seems to be working fine, but I'm having intermittent issues with the engine dying when coming to an abrupt stop. I have read some of the posts here on the Barn that discuss this issue and think I have a pretty good idea about how to proceed with correcting the problem.

My question is, do the same adjustment rules that apply to Model A Zenith carbs (float height, idle adjustment, etc.) work the same with Model B Zenith's since the Model B has a side-hung float? The B carb I'm using does not have the anti-slosh baffle in the float bowl.

'Preciate the help!
 
What engine mods, idle speed, and have you adjusted the idle air according to the owners manual? Where do you run the GAV? Is the GAV in the same position when the erratic “dying “ occurs?
 
Chuck Sea/Tac said:
What engine mods, idle speed, and have you adjusted the idle air according to the owners manual? Where do you run the GAV? Is the GAV in the same position when the erratic “dying “ occurs?
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I have a Brumfield 5.9 head, "B" grind cam, stock ignition, Model B carb and intake. I installed all new parts inside with a new rebuild kit that was made several years ago, but didn't make any changes to the float since I wasn't sure whether to change the setting or not. Idle speed might be a little high, so I'll reduce it slightly. I have the idle air screw adjusted to where it seems to idle smoothly. I usually increase the GAV setting when starting and then decrease it to where the car seems to like it after warming up and leave it there. It doesn't always die, but more often than not it has a tendency to act like it's starving. Otherwise, the engine takes throttle well and performs very nicely. I'm guessing I need to adjust the float, but wanted to make sure before I did. Is the float level the same as a regular Model A Zenith?
 
The fuel level in the bowl is the same as the Zenith Model A carb. Although many people call for 5/8" (10/16") below the gasket surface, I tend to go a bit lower, to 11/16".

It's OK to run the idle RPM up a bit on a fresh rebuild, until everything wears in and it will idle a bit better.
 
The Model B carburetor also had a float chamber baffle that is usually missing. I put the baffle back in mine and adjusted the float level with a carburetor fuel level setting gauge and no longer have issues when coming to a stop.
 
rich40701 said:
The Model B carburetor also had a float chamber baffle that is usually missing. I put the baffle back in mine and adjusted the float level with a carburetor fuel level setting gauge and no longer have issues when coming to a stop.
Click to expand...

After further review, I noticed that I have a second Model B carb WITH the float baffle. I think I'll install the baffle in the carb I'm using then check the float adjustment to be sure it's spot-on.
 
I was given a bunch of mismatched rusty B carbs. So far I have built 3 that do not stall when braking. I am still stumped as to why some will stall and others not. I worked for days on one carb and it still stalled no matter the adjustments with and without baffle. On this one, I just used another top piece and moved float etc to it and it no longer stalled. I am using an ultrasonic cleaner to clear passages and new jets from Renner. I have found there are a few variations of the B carb from my collection. Raised Zenith lettering is the B2, indented lettering is the B1. I have three versions of lower body where the float chamber has no shelf on a B1 and two versions on B2 shelf. Also, some lower bodies use a smaller jet than others and are not interchangeable, maybe a tractor or other application? Some of the carbs have to have the idle screw closed all the way, another cracked open a bit. GAV opened 1/8 to 1/4 turn. A constant idle speed is hit and miss, two idle great the third not so great. The third is back in the ultrasonic cleaner cooking maybe a blocked passageway. With all the hours I have put in these carbs I should have all the answers, I am still stumped. In my experience, the Viton float valve works the best, a new standard valve leaked.
 
goldie,
Always helps to hear about others' experiences when fiddling with these old carbs. They don't always behave the way we expect them to! Thanks for your input and keep us updated with your findings.
 
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