Shaggy

Member
The problem is that the tractor won't run unless you have the choke half closed.
The carb has been rebuilt by a shop and it has been taking apart and recleaned several times.
All the jets have been poked and prod to make sure nothing is blocking them.
We even redrilled the main jet 2 sizes bigger.
It also has new manifold gaskets.
Sprayed around everything checking for vacuum leaks and haven't found any.
Any ideas? Its a 62 series carb.
Thanks!
 
Have you checke in the tank? Is there something blocking the flow of fuel from the tank to the carb?
I have an inline fuel filter on my DC.
 
The tank is very clean and the fuel line and sediment bowl in new.
What is the economizer jet for?
 
Check fuel flow next. Take the plug out of the bottom of the carb & drain a pint out. Flow should not change, should be steady. Get back to us.
 
The flow is good!
Im thinking about making the main jet a few sizes bigger again. It seems to be starving
 
I had one that had been rebuilt professionally that refused to run over 30 seconds My buddy finally discovered that the shaft the float pivots on was bent slightly. He straightened it and now the old CC runs as good as ever.
 
I turned it out to the point that is was about to fall out! And that was after I went 2 sizes bigger on the jet size.
To me that economizer jet it leaning it out to much. It has a passage just south of the choke butterfly all the way to the throttle butterfly
 
Shaggy,Check the gasket between the carb halves for proper hole alignment like Lazy WP said.It could be flipped over and is blocking a hole.Also make sure it is the correct gasket for your carb.I have found the wrong gaskets in carb kits before.
 
(quoted from post at 18:18:29 03/04/15) Shaggy,Check the gasket between the carb halves for proper hole alignment like Lazy WP said.It could be flipped over and is blocking a hole.Also make sure it is the correct gasket for your carb.I have found the wrong gaskets in carb kits before.

The main jet will not help ur idle problem; the idle circuit is a separate circuit that is adjustable by the upper small adjustable jet. I would almost bet there is a passage in the main carb body where the fuel is metered down to the main discharge nozzle at idle, they would be the small vertical passages that go straight down to the adjusting needle, check them, if the tractor will run at rpm it should have enough flow to idle.

Mel
 
If everything else checks out, I would raise the float level. Carburetor bowl may not be filling up enough.
 
It doesn't want to come up on Rpms unless you have the choke halfway on and as soon as you open it will die
 
I am only going to print a small portion of the info I can email you It includes the Model TSX Carburetor, Marvel-Schebler Carburetor and zenith 61 & 161 these are very similar to what you have it includes repair procedures and parts list. If you want a copy Its 20 pages no charge to anyone email me @[email protected] This is very lengthy

ZENITH 61 AND 161 SERIES CARBURETORS
Fig. S-22
The Zenith 61 and 161 Series carburetors are
of updraft single venturi design. They are made
in 5/8" and %$" S.A.E. barrel sizes; with 5/8 ", 7/8",
1" and 1 14" S.A.E. flange sizes available. They
are made with selective fuel inlet, with or without
a back suction economizer and a main jet
adjustment.
They are "balanced" and "sealed," and the
semi - concentric fuel bowl allows operation to
quite extreme angles without flooding or starving.
This design makes them particularly adaptable to
smaller farm tractors and a great variety of
agricultural machines and industrial units.
MODEL DESIGNATION
Type—Updraft.
Material—Barrel and bowl castings, cast iron.
Styles—"A" Throttle and choke shafts parallel.
"D" Equipped with degasser assembly.
"E" Elbow air intake.
"J" Back-suction economizer.
"R" Built-in governor.
"S" Straight through air intake.
"X" Flange next size larger than standard.
"XX" Flange second size larger than
standard.
Size
Designation
Nominal
Size
Throttle Bore
Diameter
Flange Size
S.A.E. Standard
5 5/8" .787 or Ii"
7 /8" 1.023 or 1A" 7/8"
X7 7/8" 1.023 or 11;2" 1"
XX7 7/8" 1.023 or 1A" 11/4"
8 1" 1.181 or 1A" 1"
FUEL SUPPLY SYSTEM
The fuel supply system is made up of the
threaded fuel inlet, the fuel valve seat, fuel valve,
float and fuel bowl.
The fuel supply line is connected to the threaded
inlet. The fuel travels through the fuel valve
seat and passes around the fuel valve and into the
fuel bowl. The level of the fuel in the fuel
chamber is regulated by the float through its
control of the fuel valve. The fuel valve does not
open and close alternately but assumes an opening,
regulated by the float, sufficient to maintain
a proper level in the fuel chamber equal to the
FUEL SUPPLY SYSTEM
Fig. S-23
demand of the engine according to its speed and
load.
The inside bowl vent as illustrated by the passage
originating in the air intake and continuing
through to the fuel bowl, is a method of venting
the fuel bowl to maintain proper air fuel mixtures
even though the air cleaner may become restricted.
This balancing is frequently referred to
as an "inside bowl vent."

IDLE SYSTEM
The idle system consists of the idle discharge
port, idle air passage, idle adjusting needle, idle
jet, and fuel passage.
The fuel for idle is supplied through the main
jet to a well directly below the main discharge
jet. The pick-up passage is connected to this
well by a restricted drilling at the bottom of this
passage. The fuel travels through this channel
to the idle jet calibration. The air for the idle
mixture originates back of (or from behind) the
main venturi. The position of the idle adjusting
needle in this passage controls the suction on the
idle jet and thereby the idle mixture. Turning
the needle in closer to its seat results in a greater
suction with a smaller amount of air and therefore
a richer mixture. Turning the needle out
away from its seat increases the amount of air
IDLE SYSTEM
Fig. S- 24
and reduces the suction. and a leaner mixture is
delivered. The fuel is atomized and mixed with
the air in the passage leading to the discharge
port (or priming plug) and enters the air stream
at this point.
HIGH SPEED SYSTEM
The high speed system controls the fuel mixture
at part throttle speeds and at wide open
throttle. This system consists of a venturi, controlling
the maximum volume of air admitted into
the engine; the main jet, which regulates the
flow of fuel from the float chamber to the main
discharge jet ; the well vent, which maintains
uniform mixture ratio under changing suction
and engine speeds; and a main discharge jet,
which delivers the fuel into the air stream.
The main jet controls the fuel delivery during
the part throttle range from about one-quarter
HIGH SPEED SYSTEM
Fig. S-25
to full throttle opening. To maintain a proper
mixture ratio a small amount of air is admitted
through the well vent into the discharge jet
through the air bleed holes in the discharge jet
at a point below the level of fuel in the metering
well.
The passage of fuel through the high speed
system is not a complicated process. The fuel
flows from the fuel chamber through the main
jet and into the main discharge jet where it is
mixed with air admitted by the well vent, and
the air-fuel mixture is then discharged into the
air stream of the carburetor.
BACK SUCTION ECONOMIZER SYSTEM
Fig. S- 26
ECONOMIZER SYSTEM
The economizer system consists of a "milled"
slot in the throttle shaft, which acts as a valve
to open or close the system ; a vacuum passage
from the throttle bore to the slot in the throttle

SECTION 5, FUEL SYSTEM
shaft; and a vacuum passage from the slot in the
throttle shaft to the fuel bowl.
This system allows economical fuel mixture
ratios for part throttle operation while still permitting
the richer mixture ratios that are needed
for full load operation.
The economizer system performs its function
by establishing a "back suction" on the fuel in
the fuel bowl during most of the part throttle
range of operation. This "back suction" is created
by manifold vacuum, through the channels connecting
the throttle bore with the fuel bowl. This
retards the flow of fuel through the metering
systems and thus permits the carburetor to operate
on leaner part throttle mixture ratios.
The rotation of the throttle shaft controls the
economizer system. During part throttle operation
from about one-quarter to three-quarters
throttle, the passages are open and the pressure
in the fuel bowl is lowered. This retards the flow
through the main jet and a leaner mixture is
supplied. pn full throttle opening the passages
are closed and the main jet flows to full capacity
to supply the richer mixture required.
CHOKE SYSTEM
The choke system consists of a valve mounted
on a shaft located in the air entrance and operated
externally by a lever mounted on the shaft.
The choke valve is used to restrict the air entering
the carburetor. This increases the suction on
CHOKE SYSTEM
Fig. S-27
the jets when starting the engine. The choke
valve is of a "semi-automatic" type, having a
poppet valve incorporated in its design, which is
controlled by a spring.
The poppet valve opens automatically when the
engine starts and admits air to avoid over-choking
or flooding of the engine. The mixture required
for starting is considerably richer than that
needed to develop power at normal temperatures.
As the engine fires and speed and suction are increased,
the mixture ratio must be rapidly reduced.
This change is accomplished through adjustment
of the choke valve and the automatic
opening of the poppet valve to admit more air
when the engine fires.
 
Shaggy I would not drill the main jet bigger because this carb was engineered and designed for that size jet. If when they did the rebuild they installed improper replacements , You may never know unless you replace them yourself.. The 61 & 62 are very similar as you will see in the pictures both had an economizer feature on them A low vacuum system. Now I don't have a picture of the 62 I can send you but it is visible online and you can buy it and download it for I think 5 bucks. However it is no where near as complete as what I wanted to email you. I'm sorry I cant find the 20 pages online anymore for you to download yourself.
 
Here is my Email.
[email protected]
I appreciate any help I can get with this carb!
Normally I have pretty good luck with them.
It will idle like a dream with the choke off but don't try and open the throttle!
It is spotless inside! And plenty of fuel in the bowl.
 
(quoted from post at 20:55:07 03/06/15) Here is my Email.
[email protected]
I appreciate any help I can get with this carb!
Normally I have pretty good luck with them.
It will idle like a dream with the choke off but don't try and open the throttle!
It is spotless inside! And plenty of fuel in the bowl.

If the fuel bowl has plenty of fuel and it runs a steady stream out of the carb bottom drain then the main discharge nozzle has go to be holding the fuel from flowing. with the main jet completely removed you should have a steady stream out the jet opening, if not explore the floor of the carb where the fuel exits the float bowl, if the fuel is flowing out the jet opening it should flow through the drilled jet and srtraight through the discharge nozzle, that is the angled brass piece that sticks up into the venturi.

This is probably a stupid question but the venturi was installed wasn't it, I had one onetime that the venturi was not put back in. It should run with the high speed circuit as that is most direct, out the bottom of the float bowl through the main adjust jet and right into the discharge nozzle. remove the main discharge nozzle and make sure you can find no dirt between the jet you drilled and the nozzle opening

While not as simple as the M/S carbs they are not difficult to figure out.

There is a setting for the float level and that should be set exactly to spec as it sets the fuel level at the nozzle opening and to high it will spill over and flood and to low will be harder for the engine vacuum to pull into the airstream. Carbs are designed or a specific setting and should work as designed, bending the float arms is trying to make for some other fault, if right, the float arms and float will be parallel with the carb gasket surface and if looked at front to rear they will be vertical, not twisted or tipped toward or away from each other.
 
I sent you the Manual I have as you can see there are a lot of variable's. You should be able to figure it out now. My guess is your not getting proper vacuum (low vacuum) through the carb ports this would explain why you have to choke it so much. If you have not already blow compressed air through all ports in both directions do so and make sure it comes out as it should. Pay special attention to obscure areas Don't run any wire or similar through it you may increase the restriction hole size. The float level should be is 1 inch 39/64 or 1.609 From the bowl surface to the top of the float pontoons no gasket.
 
One other thing make sure your plug wires have spark your points are correct and are installed properly if you like just swap the number 2 and 3 wire in case you have the rotation wrong. This condition you discribe sounds a little like mixed rotation although you did not say it was back firing just something else to look at. good luck
 
I just thought about you saying you didn't know if it was maintaining fuel in the bowl. You can get a thin piece of clear flexible plastic tubing and use it as a sight guide. That is like a water level. If you can put the tube in the fuel drain port so it don't leak at the same time tape it to the outside of the bowl, since liquid will find its own level the outside level of fuel in the tube will be the same as the level of fuel inside the bowl. I do NOT know the level of fuel in the bowl on a 62. However the 61 & 161 should be 7/16 or 0.4375 from the top of the fuel level to top edge of the bottom portion of the fuel bowl. This would be much like a sight glass they used years ago on many things to monitor fuel tank levels. I also made one from a coffee can to level a foundation I found it had more accuracy than a laser level particularly at longer distances. Hope this helps!
 

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