Johnson Carburettor

[B Bouchier]

Johnson Carburettor for 1929 Cadillac 341B
I am having problems with the carby leaking petrol into the valley of engine.
The carby has had a rebuild kit through it but it doesnt seem to fix the problem
Also the motor is running too rich.
I do not seem to be able to find any instructions as how to set the carby up
Any help would be appreciated
Brian B

[Big Fins]

Never even having seen a 1929 engine other than in pictures, may I suggest that the float in the carburetor is sticking open allowing the petrol to overflow the bowl and onto the engine. It may also be allowing it to overflow the bowl and down the throat of the carb and into the engine.

Please don't try and run this as you may lose that beautiful 1929 to a fire. 1929-1931 were the most beautiful Cadillacs ever made.

[wheikkila]

Being a 29 I would assume it has a updraft carb. I would be checking the float.
        Thanks Wayne

[Mike Baillargeon #15848]

Here's some pictures of my 29 Roadster....working on the carb ain't easy....heck taking pictures of this updraft Johnson was a real chore....

Get a mirror and a drop light in there and see where it's leaking from.....Is there a petcock shutoff at the bottom of the fuel pump?...If so, shut it off there for now...

Maybe the fuel fitting at the carb is loose....maybe the seal between the bowl and carb body isn't good....

We gotta fix that fuel leak before moving on to the carb adjustments....car has to be running for that....

Mike

[B Bouchier]

Thank you for the info and pictures
The carby is an updraught the same as in the pictures
It has a new needle and seat and all new seals.
The float is correct as per the owners service manual and the needle is moving freely
No leaks at fittings.
Leak seems to be coming out the bottom of bowl.

[wheikkila]

Is there a drain on the bottom of the bowl? I haven't worked on any of these. But I have worked on Packard's, Reo's and a whole lot of Model A's.
                        Thanks Wayne 

[Mike Baillargeon #15848]

Is there a drain on the bottom of the bowl? I haven't worked on any of these. But I have worked on Packard's, Reo's and a whole lot of Model A's.
                        Thanks Wayne

I don't remember a drain on the bottom of the bowl....It's like a lawn mower....just a bolt holding the bowl against the carb body....maybe that bolts gasket is bad?

Mike

[fishnjim]

My book only goes back to '35.   But two things come to mind.
From troubleshooting training, if it didn't leak before and leaked after repair, then the repair is at the source of the issue.   {I'm not a pre-waree, but some of these period carbs also pull vacuum to draw in gas from the tank, so that system could be involved if getting too much fuel.}   [My guess is the bowl is not on right, as it's leaking, and maybe the nut is cross threaded]
Try Straight-eight.com   They do work in this era.

[Jim Stamper]

 If it is not a straight forward missing screw or similar thing, I would guess the float is set too high to close off the source. What is the float, the old cork float that may not float as well as it once did or is it a newer brass float with slightly different characteristics from a loggy cork float, so the cork instructions may not be the thing for a brass float.
     While it is out why not try hooking a mower gas tank to it to see just where it leaks and if the float is adjusted pre-check it before re-installing it. If it still leaks out of the car, keep looking it won't do any better after the trouble of re-instaalling.

     These carburetors come out fairly easily after a time or two once the sequence is worked out. Less than 5 minutes with my old LaSalle.

[B Bouchier]

The carby was leaking before the kit was put through it.
It is leaking out the hole at the bottom of the bowl, the hole inside the brass nut that holds the bowl on.

[Big Fins]

Is it possible the bowl was over tightened and stripped that brass nut? There may also be a crush washer or similar gasket under the head of the bolt that split or went missing.

[Alex D.]

There have been many discussions over on the AACA forum regarding the troublesome Johnson used on early Cadillacs. I'm sure you will get some advice from some very knowledgeable members like Carb-King and Edinmass.

[fishnjim]

That must be the drain hole, so nut is not engaging as I suspected to shut off.  Missing a gasket, or part or not threaded properly/stripped out.
But go to the guys that know this better.   Lost without a diagram, etc.   

[pmhowe]

Brian,

The Johnson carburetor has a very bad reputation for leaking. I second Alex Dunkle's suggestion: Please go onto the AACA forum and google Johnson Carburetor. Then contact  carbking  or Ed Minnie for a solution.

Merry Christmas!

Phil

[Chris Cummings]

Hi Brian,

Sorry to be so late to the party, but the Chinese virus got in the way.

First thing.  Cadillac expected that these carburetors would do some dripping.  On the 1930 and 1931 V-8 engines, you will notice a little hole at the bottom of the vee between the cylinder banks (directly underneath the carburetor).  That passageway leads through the crankcase casting and out the right-hand side, where an attached metal pipe carries drips down to the road.  (I'm not closely-enough acquainted with the 1929 V-8 engines to say if they have a similar arrangement.)  The 1930-'31 V-16 cars, with their carburetors carried next to the engine, were originally built with little stamped funnels attached to the frame side rails to catch drips from underneath and carry them outboard of the frame.

That having been said, it sounds like your fuel bowl is overflowing and the overflow is exiting the carburetor through the main air passage.  That can happen for a number of reasons.  (1) If the needle valve seat doesn't seal against the carburetor body (there's a little fiber washer between the seat and the carb body); (2) if the needle valve does not seal properly in its seat (sometimes you have to lap the needle into its hole to get a good seal); (3) sometimes the float rubs against the inside of the fuel bowl, preventing the needle valve from being pushed properly into its seat (gentle sanding in the area of any contact works and does no harm); (4) the float needs to be buoyant enough to seal off the needle valve as needed.  (5) the cantilevered hinge for the float is complicated, and its parts must be free to move or you can have problems; (6) the adjustment of the float's maximum upward movement is made with the carburetor upside down, it's done by bending the hinge bracket, and it's not really shown in the 1929 shop manual. 

The later (1930-1931) shop manual has much more detailed illustrations for adjusting the internals of these carburetors, and you might want to invest in one of the copies available on e-Bay.  The 1929 carburetor is similar enough to the 1930-31 model to make this helpful.

By all means, contact Ed Minnie and carbking. 

I hope what I have written assists you.

Best regards,

Chris Cummings