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Old 05-20-2019, 02:54 PM   #1
djlanier
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Default Need Help with Model B Carb

I’ve been trying to adjust the idle on the Model B carb on my ‘28 roadster. However, no adjustment to the idle air mixture screw will cause it to stall. In fact, when I near all the way CW it seems to rev up a little. According to Les Andrews’ book this indicates an air leak in the intake system. All I can find is by spraying carb cleaner around the throttle shaft the rpm will pick up slightly. What is the best way to remedy this? The engine requires very little choke to start cold but when I do choke it I find a little fuel on the bottom of the carb around the drain plug.
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Old 05-20-2019, 04:04 PM   #2
MickeyT
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Default Re: Need Help with Model B Carb

Just some ideas. Pull the drain plug on the carb. and make sure the main jet is tight. Check the throttle shaft and check if it's not too loose. Then check the wiper vaccum line all the way back. Easiest to disconnect it and plug. Lots of places to loose vaccum. Completely closing the idle mixture screw should cause the engine to die. Do you have a good gasket on the carb. to manifold mount?
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Old 05-20-2019, 04:56 PM   #3
djlanier
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Default Re: Need Help with Model B Carb

I pulled the drain plug and the main jet is tight. Throttle shaft does have some slop in it, can pull it back and forth (or in and out) probably 1/8”. Don’t have a vacuum wiper line, plug in manifold is tight. Engine doesn’t die when idle mixture screw is closed. I did take it out though and it has a small score all the way around it about eighth inch from tip, but it seems minor. I had it set 1 1/2 turns out before trying to adjust idle. There’s a good gasket on carb to manifold mount.
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Old 05-20-2019, 05:23 PM   #4
Sparky
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Default Re: Need Help with Model B Carb

One of my B carbs had a clogged idle passage, you may want to check it.
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Old 05-20-2019, 06:59 PM   #5
30 Closed Cab PU
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Default Re: Need Help with Model B Carb

If you over choke the carb, gas can flood the carb and it can come out the intake/weep hole, drain down the body of the carb, and drips off the drain plug or carb bolt head.. If it happens again use your small finger on the inside bottom of the intake and see if there is gas. This does not tell you what is wrong, just how you are getting the gas drippage.
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Old 05-20-2019, 09:32 PM   #6
djlanier
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Default Re: Need Help with Model B Carb

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I’ll check the idle passage, haven’t tried that. I’ll bet that the leak is coming from weep hole, I can’t find anything else leaking. It isn’t much but it shouldn’t be dripping at all and it’s only at start-up.
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Old 05-20-2019, 11:37 PM   #7
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Default Re: Need Help with Model B Carb

My motor cold starting procedure is set spark retard lever all the way up, idle lever set to where it just starts to pull the accelerator pedal down, set the GAV 1/2 to 1 turn open. Ignition on, pull choke out all the way, press the starter and on 2cnd revolution push choke full in/un-choked. Motor immediately fires. Set spark lever 1/4 down. Adjust idle and GAV for smoothest running. Continue to adjust GAV and idle lever as motor warms up.


In the beginning of owning my A I had a tendency to pull the choke out until the motor was running. That is not the corrrect way. This has a tendancy to flood the motor/carb. The purpose of full choke is to load Intake manifold/motor with rich fuel mixture, sort of "primes" the intake manifold. Then when the choke is released there is an increase of air/leaner fuel mixture which helps push fuel/air into the motor, and then the motor fires. Continuing to hold full choke tends to floods the carb/Motor.


Do not know if this is your issue, perhaps you are already aware of this info.
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Old 05-21-2019, 08:59 AM   #8
djlanier
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Default Re: Need Help with Model B Carb

My cold start procedure is very similar to yours, I only choke 1 or 2 revolutions and it starts fine. My problem began in attempting to get to a slow idle. It doesn’t respond to the idle air mixture screw. I don’t know if the slight carb leak at startup is related to that or not. Does seem to be a slight air leak at the throttle shaft and there is minimal movement when I pull out on it. I do appreciate yours and the others’ responses.
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Old 05-21-2019, 09:52 AM   #9
30 Closed Cab PU
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Default Re: Need Help with Model B Carb

The idle mixture screw is set at very low idle, below 500 rpm. You can tell you are idleing slow enough by turning the GAV. at very low idle GAV is ignored/does not do anything.




My point is are you able to idle that slow?
You can try this procedure


https://www.model-a.org/installing_carb.html
There is a lot more really great info on this site.
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Old 05-21-2019, 09:57 AM   #10
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Default Re: Need Help with Model B Carb

Just realized that your is a Model B carb, most info is for the model As Zenith 1 and 2 carbs I do not know if they adjust the same way.
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Old 05-21-2019, 10:12 AM   #11
Bob C
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Default Re: Need Help with Model B Carb

This is what the June 1932 Service Bulletins has to say about the GAV on the B carb.
"The valve should be turned back (clockwise) as soon as the engine has
become warm. Advise owners the car should never be operated with this
adjustment open."


Bob
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Old 05-21-2019, 10:30 AM   #12
Ernie Vitucci
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Default Re: Need Help with Model B Carb

Good Morning all...Dave Renner at Renner's Corner 734-428-8424 has a good reputation for providing correct jets and often, over the years, the wrong jets have found their way into these carburetors and they don't run as they should. Give him a call and see if he can help you...also you could have a bad float valve or a heavy oversize float...bad floats will definitely make you say bad words and think bad thoughts! Ernie in Arizona
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Old 05-21-2019, 11:14 AM   #13
Jerry in Shasta
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Default Re: Need Help with Model B Carb

Check the idle port, very small and easily plugged. I straighten out a large fish hook and use the sharp point to clean the port. Then blow it out from the
throat side
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Old 05-21-2019, 04:52 PM   #14
djlanier
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Default Re: Need Help with Model B Carb

Jerry in Shasta, is the port in the upper casting? Is this the same thing Sparky mentioned as the idle passage? I haven’t identified it with my drawings. There is an opening in the throat just above the throttle plate but it’s closed with a small brass screw.

30 closed cab PU, it will idle slow enough that GAV doesn’t affect it. And Bob C I had read on here to leave GAV closed, it even starts well closed.

I have a good Model A Zenith but would really like to get “B” adjusted properly. I bought it on Ford Barn and had it professionally rebuilt locally. It ran well on his dynamometer.
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Old 05-21-2019, 05:39 PM   #15
Chuck Sea/Tac
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Default Re: Need Help with Model B Carb

Does the throttle shaft move up and down, or back and forth. ( not in and out) which it really shouldn’t? You saying spray around the shaft picks up rpm tells me you need to repair. 1 way is to solder it up. Another is to use an oversized shaft, or drill and bush. But it won’t idle right with a worn shaft
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Old 05-21-2019, 06:42 PM   #16
djlanier
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Default Re: Need Help with Model B Carb

I think it’s the throttle shaft. Put my Model A Zenith on this afternoon and it runs fine. Which is the better repair? I don’t have a drill press.
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Old 05-21-2019, 07:35 PM   #17
Ed in Maine
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Default Re: Need Help with Model B Carb

You might be able to tighten up the throttle shaft by adding some solder to the the brass shaft. Then carefully file it around for a snug fit. Also, you should check the idle jet flow rate to be at 43-47 ml/min. per Rex Reheis, Restoring Model A & B Carburetors, page B-15. Ed
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Old 05-21-2019, 09:04 PM   #18
Keith True
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Default Re: Need Help with Model B Carb

It's been a while since I had a B carb apart.But,I think the throttle shaft can't really be soldered up and filed like the A.I think it has a step,or cut out in it,and a passage in the body that lines up with it.When it is in a certain position it allows fuel to run through it from the passageway that lines up with it.You can't just bush it,because you can't plug up that passage.I can't remember if that passage is for idle,or off idle enrichening.
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Old 05-22-2019, 09:53 AM   #19
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Default Re: Need Help with Model B Carb

Quote:
I bought it on Ford Barn and had it professionally rebuilt locally.
Quote:
Throttle shaft does have some slop in it, can pull it back and forth (or in and out) probably 1/8”.
Doesn't say much for the rebuilder.
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Old 05-22-2019, 10:11 AM   #20
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Default Re: Need Help with Model B Carb

Seems it may be time to contact the rebuilder, politely tell him the symptoms and what you have found . Get him to repair it properly. Approach it right and see if he will make things right. If you start working on it, gives them an opening to say it is your fault.
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Old 05-22-2019, 07:21 PM   #21
djlanier
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Default Re: Need Help with Model B Carb

Excellent idea, thanks! Thanks
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Old 05-23-2019, 04:44 PM   #22
Chuck Sea/Tac
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Default Re: Need Help with Model B Carb

Quote:
Originally Posted by Keith True View Post
It's been a while since I had a B carb apart.But,I think the throttle shaft can't really be soldered up and filed like the A.I think it has a step,or cut out in it,and a passage in the body that lines up with it.When it is in a certain position it allows fuel to run through it from the passageway that lines up with it.You can't just bush it,because you can't plug up that passage.I can't remember if that passage is for idle,or off idle enrichening.
The backside usually doesn’t have the wear. It’s the throttle rod side. I’ve soldered mine a couple of times over the years. I bought this military grade gas resistant grease that was mentioned here a while back and use it to lube the shafts.
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Old 05-24-2019, 10:14 AM   #23
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Default Re: Need Help with Model B Carb

Quote:
You can't just bush it,because you can't plug up that passage.
Isn't it possible to drill holes in the bushing before installing it?
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Old 05-24-2019, 07:27 PM   #24
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Default Re: Need Help with Model B Carb

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Originally Posted by Chuck Sea/Tac View Post
The backside usually doesn’t have the wear. It’s the throttle rod side. I’ve soldered mine a couple of times over the years. I bought this military grade gas resistant grease that was mentioned here a while back and use it to lube the shafts.
Chuck is right. It is usually the front (throttle arm) side that has the wear. Solder it up for a tighter fit as is often done on Model A shafts and be done with it.
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Old 05-26-2019, 02:58 AM   #25
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Default Re: Need Help with Model B Carb

Are Renners Corner still rebuilding B carbs for customers or do they only supply parts for them now?
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Old 05-26-2019, 04:13 AM   #26
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Chuck and Ursus how do you solder up the throttle side?

Paul
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Old 05-26-2019, 01:09 PM   #27
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Chuck and Ursus how do you solder up the throttle side?

Paul
Remove the shaft, clean it well, then measure it with a micrometer. They tend to wear oval, with most wear on the side bearing the most tension from the accelerator spring. Apply flux and butter on a thin coat of solder to the worn side. Use a fine file to shape it to a just-to-tight fit then finish fit it with sand paper.
Or, you can buy a new one from Bratton's for $22.
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Old 05-26-2019, 04:48 PM   #28
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Default Re: Need Help with Model B Carb

Ursus
Thank you for the detailed explanation.
Some thing new for me to experiment with.

Paul
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