Tip By Mo...
Carburetor Pump Around (read everything and
understand what is happening before you start)
for the Pump Around:
evolved to the point where many engines are using a float-type
carburetor. While it works well for motorcycles, it can be a real pain
to tune for the kart application. Mainly this is due to the fact that
the fuel has the tendency to crowd up against the float bowl side wall
while going thru the corners and produces a 'flat spot' or
hesitation when you step on the throttle. The pump around
eliminates this by maintaining a constant level of fuel in the float
bowl and not depending on the floats to keep this level accurate.
photos are of a 36mm flatslide Mikuni but the application will work on
any 'Float-Type' Carburetor.
How To Do It:
thing to do is to remove the float bowl and then proceed to remove the
floats, needle plunger, and needle seat. These items are not used in
find a Two-Stage
Fuel Pump or two single stage pumps can be
used with a pulse Tee.
This is a Two Stage.
piece of tubing that is the same size or slightly larger than the
fuel inlet hose
(either copper or aluminum). This tubing is how you maintain a constant
level of fuel in your carb. Notice how it sticks into the float area
(the height you want the fuel in the bowl area). In this photo, the
tube is cut off on an angle. While this is not necessary it makes a
nicer looking modification and it's easier to determine the fuel
This tube is held in place with either JB Weld (least desirable),
Devcon-F Putty from Loctite (most desirable), or some type of Epoxy
that is not affected by the fuel you plan to use.
The next thing to do is to locate some neoprene or vinyl type sponge
material. This material can not be affected by the fuel that you are
planning to use. You can also use some 'Fuel Cell Material' if you can
afford it or find a race builder that has a destroyed fuel tank and rob
a piece from it. Cut 2 small pieces that will fit loosely on each side
of the float bowl (and not interfere with anything else). Do Not Glue
Them In Place. Let them fit loosely.
The next thing to do is to locate a fine screen
mesh (use brass to prevent rusting). Cut a template that will fit into
the bowl area. This screen does nothing more than prevent the sponges
from interfering with the main jet. Again, Do Not Glue It In Place.
not least, is the venting of the float area. What we done here is to
connect both vent nipples together with a common hose and just cut a
small notch in the top of it. Works great.
the float bowl onto the carb, hook up the fuel lines and you are ready
organization allows this type modification and even encourages this
type of innovation, however, other organizations do not encourage it
and will use it as a way to DQ you if it is not done correctly.
Sometimes this modification must be done entirely thru the bowl area
(think about it, it is possible) to keep from breaking any rules.