7arburetor Butterflies
moving the cam appreciably. Now the lift at TDC meas-
uring process can be repeated. If the above operations
have been performed accurately, the lift should be nearly
equal on both the intake and exhaust tappets. Very small
adjustments can be made by rotating the sprocket within
the clearance of the index pin.
Once the
cam timing has been adjusted, the proper
index holes should be marked permanently. Also, cor-
responding marks should be scribed on the sprocket outer
rim and the cam box with the crank at TDC for future
reference.
Head Bolts
If the cylinder head has been milled, the head bolts must
be shortened. In fact, it is a good idea to cut about 118
inch off the threaded end even if the head hasn't been
milled. This will ensure that the bolts won't bottom out
in the block threads and give a false torque reading be-
fore the head is seated properly
Pan
Baffle
Trial fit the oil pan baffle, which fits between the block
and the oil pan, and rotate the engine to check for clear-
ance. If it touches any place, bend the baffle as required to
ensure a small amount of clearance to the crank and rods.
CARBURETOR AND INTAKE MANIFOLD
MODIFICATIONS
The carburetor and manifold must both be opened in-
ternally as much as possible to allow maximum air flow
through the engine.
Carburetor
The 32DMTR carburetor allowed on the 1300 engine
and the optional 34DMTR carburetor allowed on the
1500 engine are virtually identical except for the butter-
fly sizes and some minor jetting differences. Thus, unless
otherwise noted, the described modifications apply to
either carburetor.
Disassemble the carburetor completely. Bore the
venturis to about
28mm. (At about 28.5mm they will fre-
quently break through to the outside).
Reshape the bottom of the venturis to blend into the
throttle bore with a form tool.
If desired, the throttle shafts can be ground, along
the section which fits the throttle bore, to about
118 inch
total thickness, normal to the throttle butterflies. Smooth
the edges down to feather them into the throttle plates.
If the throttle shafts are ground thin, the throttle
plates can be soldered
in
place and the screw holes filled
with solder by placing a large wood dowel behind them
to prevent the molten solder from running through.
Countersink the screw holes somewhat on each side of
the throttle shaft, so that the solder plugs will be locked
in place and won't fall out from vibration.
Plug the fuel return fitting and the vacuum fittings
on the outside of the carburetor with solder. If the car-
buretor is fitted with a float bowl vent tube, don't plug it.
For
the 1300 engine, use a 175 needle and seat (Weber
PIN 79507.175). On the 1500 engine a 200 needle and
seat is suggested (Weber
PIN 79507.200).
The fixed idle jets can be opened up to about lmm
on both the primary and secondary. 1.35mm main jets
and 1.40rnm air correction jets can be used on both sides.
This combination will be close enough to allow fine tun-
ing. Set the float at 7mm. To minimize fuel starvation
problems during cornering, the floats should be cut off
at an angle on the outboard lower corners. Cut them off
from the mold parting line, on the outboard surface, to
about 511
h
inch from the inboard lower corner. If this
isn't done the fuel climbs the outer wall during hard cor-
nering and lifts the outboard float high enough to shut
off the needle and seat and hold it shut off until the fuel
level drops too low to feed both main jets. Thus the en-
gine will start to lean out and die part way through the
corner. Cutting the floah will help minimize this problem
but may not completely cure it.
When using the 32mm carburetor, the superjet air
bleed in the carburetor cover must be plugged by solder-
ing it shut. Also, the
superjet fuel jet must be drilled to
1.30mm. The 34DMTR comes with a blank (undrilled)
air bleed jet and a large fuel jet. This richens the mixture
at the top end when the superjet comes in.
On the 32mm carburetor, when the venturis are bored,
a bleed hole is opened up into the idle circuit. This must
be plugged. The idle circuit should not be plugged, how-
ever.
A
small lead plug on the outside
of
the carburetor
(primary side) can
be
removed for
access
to
this
bleed
hole. Tap this hole through into the primary venturi bore.
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