Yamaha JT1 Series Service Manual page 49

ENGINE
·Carburetor
A. Checking the Carburetor
1) Float
Remove the float and shake it to check if gasohne 1s inside. If fuel leaks into the float while the engine ls running,
the float chamber fuel level will rise and make the fuel mixture too rich. Replace the float
if
it is deformed or
leaking_ Do not try to solder a leaking float.
2) Float valve
Replace the float valve if its seating end 1s worn with a step or if 11 is scratched. Check the float valve spring
for fatigue. Depress the float valve with your finger. and make sure that it properly seats against the valve seat.
If the float valve spring
1s
weakened. fuel will overflow, flooding the float chamber while the gas ls on.
3)Overflowing
If fuel overflows. check the carburetor as described in 1) and 2) above If neither
1)
nor 2) cures the overflowing,
it may be caused by dirt or dust in the fuel preventing the float valve from seating properly.
If
any dirt or dust
is found, clean the carburetor. petcock and gas tank
Valve seat
L
L
Float " ' "
F,g 3-19-2
4)Cleaning the carburetor
Disassemble the carburetor, and wash all its parts
in a suitable solvent
Then blow all the parts off with compressed air,
All Jets and other delicate parts should be cleaned
by blowing compressed air through them after the
float bowl has been removed
B. Idle Mixture-Idle Speed Adjustments
Dust
Fig. 3-19-3
The idle Mixture adjustment should be set exactly to factory specifications. First. turn the air screw in until it lightly
seats then back it out 1
¼
turns. Next. adjust the throttle stop so that the engine idles at 1250 ~1350 rpm.
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