The height of the metering rod in a Carter WO carburetor can be set by
using a special tool designed for this purpose. The use of three
setting tools is compared here. Obtaining the special Carter
Metering Rod Gauge is not always possible so this page also explains
some alternatives. For complete Carter WO carburetor reconditioning
instructions visit the Mighty Mo website here..... http://mightymo.org/Proj_Carter_WO_Rebuild.html
the metering rod in a Carter WO carb.
By Carl Darnell
I tried to do the best at measuring as I could because I know the info
will out there for everyone to see. I think a lot of people that
overhaul their carbs just put the new metering rod and jet in and
expect it to be the right setting. However, my finding the rods are not
the same length and while I didn't measure the depth of the taper in my
jets I suspect they vary a few thousandths as well.
Comparing the metering rod setting
In an effort to find the easiest or best way to set the metering rod I
did a comparison of the Carter tool, the Snap-On tool and the Home made
tool. I have three metering rods and jets to use to compare with a
borrowed Carter tool and a Snap-On tool and my own Home made tool.
The jet has a tapered opening of 116 deg with a hole of .070”
+.000 -.0002” as measured in the three jets I have. The metering
rods vary in length from the start of the tapered area to the spot the
pin rests on. The OAL length of the rod from the spot the pin rests on
to the tip also varies as shown below in the drawing.
Metering Rod Dimensions
I also used one
of the cleaner jets to measure the OAL of the bottom on the jet to the
shoulder of the tool for a reference and they are as follows:
Carter tool, shoulder to bottom of jet = 2.947”.
Snap-On tool, shoulder to bottom of jet = 2.946”.
Home made tool, shoulder to bottom of jet = 2.945”.
Below is a photo of the Carter, Snap-On and Home made tool. The tip
angles and lengths of the tools vary as follow.
The Carter tool has a tip angle of 58 deg with an OAL from the shoulder
to tip of 2.782”. The length of the shoulder to contact area in
jet is 2.720” and may be 2.718” as it’s hard to read
a line scratched in dykem clearly on the surface of an extremely rough
The Snap-On tool has a tip angle of 42 deg with an OAL of 2.804”
from shoulder to tip. The length of the shoulder to contact area of the
jet is 2.718” and was clear to read because the tip was very
The Home made tool I made has a tip angle of 36 deg with an OAL of
2.761”. The length of the top end to the contact area of the jet
is 2.719” The tip on my tool is as smooth as the Snap-On tool.
I measured them several times to be sure I was as correct as possible.
I used dial calipers along with a 10 power glass and a jig to hold the
rods as I made the measurements. I also used a Peak brand 10 power
comparator to do the small measurements. I was as careful as I could
but some readings could be off a thousandth or two.
Metering Rod Setting Tools
Here is a drawing of the Home made tool from the Internet that I made
to save you from looking it up. I paid close attention to getting is
exact as possible and it must have worked as will be shown in the
following tests of all three tools. You will note a dotted line on the
drawing that indicates where I ground away half of the diameter for
about ½” down the shaft to clear the backing washer on the
pin where the metering rod sits. Since the Carter and Snap-On tools are
flat stamped metal and the rod is 1/8” diameter there will be
some interference so don’t force it or you will get a false
Home Made Metering Rod Setting
Now for comparing them on the carb on my Jeep. When I checked my
current setting it had .005” free travel of the rod with the
throttle screw backed off all the way to close the throttle plate. That
means with a dial indicator on the top of the rod I could move the rod
up .005” while holding the throttle closed.
When I put the Carter tool in place of the metering rod I had to loosen
the nut and reset the pin and tighten the nut. When I checked the free
travel using the metering rod I now have .040” free travel using
the dial indicator as noted above.
Then I removed the metering rod and installed the Snap-On tool and the
setting was the same as with the Carter tool. As I moved the tool I
could just feel it touching the bottom of the pin.
Then I removed the Snap-On tool and installed the Home made tool and
the result was the same. Moving the Home made tool under the pin I
could just fell the tool as it rubbed the bottom of the pin.
All three tools gave the same setting of the metering rod pin. I
wasn’t expecting that they would be that close but they are.
Because of the differences in the dimensions of the metering rods and
possibly the jet don't expect replacing the metering rod and jet in an
overhaul without resetting the pin to end up with the correct setting.
It could be way off.
Alternate dial indicator method of
setting the metering rod
Knowing what I found a careful person with a dial indicator and
magnetic base could set the metering rod without a tool by setting the
free travel of the rod to the .040" I found mine to have after using
the correct tools. Clamping the carb to a flat metal bench and using
the mag base indicator next to it would do a good job IF YOUR CAREFUL
and use a very flat work bench or drill press table.
In the photo below I have the dial indicator set up on the exhaust
and against the head in a spot where it is solid and doesn't move. You
have to back the throttle screw off 6 full turns to be sure the
throttle plate is closed. The plunger is set on the metering rod with
the plunger as straight in line with the metering rod as I can get it.
Then I set the dial on "0" to start to set the rod. Then you loosen the
pin nut just so it will slip, push the pin down gently on the metering
rod loop bottom and then with tweezers lift the rod until the dial
indicator shows .040" and lock the pin nut. Check the travel by moving
the metering rod up and down between the jet and the pin and it should
still be .040". If not reset it until it is. It is important that the
plunger tip touch only the metering rod and not the washer on the pin.
On Vehicle Dial Indicator Metering Rod
Setting the metering rod on the bench is a little easier but you still
use the same method as above while the carb is clamped to a drill press
table. See photo below. The tip I used in the dial indicator has a flat
face but didn't screw all the way in the plunger but it is bottomed out
in the threads. You can use the rounded tip that comes with the dial
indicator but you have to be very careful to get it centered on the
metering rod and not touching the pin washer to get a good reading.
Most people would find it easier using the Carter tool or a home made