First of all, If you have not
already done so, remove the carbs from the bike. Carefully dismantle one
carb and lay out the bits in some sort of logical order on a sheet of
newspaper. Clean the crud out of the float bowl and blow through all the
passages in the carb body with compressed air.
For the next bit you will need some Loctite hydraulic
sealant (Ordinary thread lock appears to work too, we found out by
accident!) Take the jet block, this is the square block with the round
hole that goes in through the top of the carb. Turn it upside-down and you
will see a raised ring with threads in the middle. Put a thin coat of
Loctite round the outside of the ring and place it in the carb ensuring
that it is square to the carb body.
Next take the needle jet assembly that screws in
from the bottom of the carb into the jet block. Apply a thin coat of
Loctite to the threads and under the hexagon. Insert the needle jet
assembly through the carb into the jet block and tighten down. You may
have to wedge the jet block with a screwdriver to stop it rotating out of
square with the cab body. What all this does is seal the emulsion chamber
from any air leaks due to poor tolerances.
Now refit the main jet, choke jet and idle jet, also
using Loctite. There should be a little black D-shaped washer under the
idle jet. It is supposed to lock the needle jet assembly in place, which
it never does. This can be safely binned.
The next thing is to install the float. The float
needle has a tiny clear plastic ring on the end. THIS YOU MUST NOT LOSE!
If you do you will have to buy a new carb repair kit and these are
becoming hard to find. Apparently the float needle from a Briggs &
Stratton lawn mower fits but I have not checked this so far. Next place
the float chamber gasket on the face on the carb Next hang the needle from
the float and lower it into its hole at the same time as lining up the
float and spindle holes. Insert the float spindle.
Now look at the horizontal line on the side of
the float. This should be parallel with the top of the float chamber (The
book says 13mm from this line to the float chamber face on the carb body).
The little brass tang on the float chamber should be CAREFULLY bent to
make this so. The tang-to-float joint area is a weak spot and frequently
leaks. As a precautionary measure it can be filleted with a small bead of
epoxy resin. Sometimes the float legs are twisted so that you can only get
one side parallel. In this case just average the difference.
Now refit the float bowl checking that the gasket
does not interfere with the movement of the float. If it does it should be
trimmed.
More photos and details coming soon!
William Thomson
