15. Setting Ignition Timing with Dial
Indicator
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IV. SERVICE INSTRUCTIONS
A. PREPARATION FOR COMPETITION USE
1. TIMING
Tools needed for setting the timing are a dial indicator, feeler gauge,and a buzz box or circuit breaker
light. The dial indicator is either screwed into the vertical spark plug hole or mounted to one of the
cylinder head studs with a special fastening plate, if the head is removed. The points gap should be set
at .3 mm at top dead center, measured with the feeler gauge.
Next, the crank shaft is rotated approximately
45° counter clockwise. The crank shaft is then
slowly rotated clockwise until the dial shows
2.8 - 3.2 mm before top dead center for the MC
250 or 501, or 3.5 - 3.7 mm for the MC 400 and
440. The ignition points should just open at these
settings. If this is not the case, then the three
screws holding the stator plate in place should be
loosened and the stator plate should be rotated
until the ignition points open at the above settings
This should be checked with the buzz box or cir-
cuit breaker light. One lead is grounded and the
other lead is connected to the ignition points.
The stator plate is then rotated counter clockwise
to achieve more spark advance and it is turned
clockwise to achieve lessspark advance. When the
proper amount of advance is found and the igni-
tion points break the circuit at the previously
mentioned settings, then the screws holding the
stator plate in position should be re-tightened
evenly to prevent the timing from slipping while
tightening the screws. The spark advance should
be double-checked after screws are tightened to
assureproper timing.
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2. ADJUSTMENT OF CARBURETOR
The basic adjustmnet jetting of the carburetor is
shown in the technical data. Idle adjustment is
performed while engine is warm with twist grip
closed. It is regulated by moving the carb-slide
while throttle is closed with the larger screw on
the left side of the carboThe farther it is turned
in (clockwise), the higher the idle. The mixture
at idling R.P.M. is regulated with the air adjust-
ment screw which is located directly behind the
idle adjustment screw. The more this screw is
turned in (clockwise), the richer the mixture.
The basic setting should be 1ito 2 turns out
(counter clockwise) from the point where the
screw is bottomed out. Each engine must be indi-
vidually jetted and adjusted.
Other factors to be considered when jetting car-
buretors are humidity, altitude, type of fuel and
mixture ratio. etc. Jetting should always start
with the larger jet sizesand then work down from
there to prevent seizure. With proper jetting, the
spark plug should have a tobacco brown color.
(The spark plug MUST be the proper heat rangel)
16. Setting
U.
Tuning Carburetor
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