Onan NHC Series Operator's/Service Manual And Parts Catalog page 161

FUEL SYSTEM
GASOLINE CARBURETOR
For correction of problems traced to the gasoline
carburetor, use ;the appropriate procedures selected
from the following sequence, referring to Figures 11
and 13.
Adjustment Under Load: Adjust the carburetor as
follows when a f u l l load can be applied.
1. Make sure the ignition system is working properly
and that the governor is adjusted.
2. Start the engine and allow it to warm up. If the
carburetor is so far out of adjustment that the
engine w i l l not start, close both needle valves
gently to their seats. Then open each 1 to 1-1/2
turns, first the idle and then the main adjustment.
3. With no load applied to engine, turn the idle adjust-
ment out until the engine speed drops slightly
below normal. Then turn the needle in until the
engine speed returns to normal.
4. Apply a f u l l load to the engine and then carefully
turn the main adjustment in until the speed drops
slightly below normal. Turn the needle out until
the engine speed returns to normal.
Adjustment Under "No Load" Conditions: When a load
cannot be applied, adjust the carburetor as follows:
1. Perform steps 1 and 2 as given under Adjustment
Under Load.
T H R O T T L E
STOP SCREW
F U E L I D L E
A D J U S T M E N T
A
1
A9f«
G J ^ M A
F L O A T BOWL N U T
A I N F U E L
A D J U S T M E N T
B
2. Pull out on the governor mechanism to slow the
unit down to about 400-500 rpm.
3. Set the idle adjustment screw for even operation'
(so the engine is firing on both cylinders and is
running smoothly).
4. Release the governor mechanism to allow the
engine to accelerate. If the engine accelerates
evenly and without a lag, the main adjustment is
correct. If not, adjust the needle outward about
1/4 turn and again slow down the engine and
release the mechanism. Continue until the engine
accelerates evenly and without a time lag after
releasing the governor.
5. With the carburetor and governor adjusted, set the
throttle stop screw at the desired idle speed.
Float-Level Check: If the carburetor adjustment f a i l s to
provide satisfactory operation, remove the carburetor
and check the float level as follows:
1. Remove the fuel line, air cleaner hose, governor
linkage and choke wires.
2. Remove the two carburetor mounting nuts and
remove the carburetor.
3. Unscrew the float bowl nut and remove the entire
main fuel adjustment assembly from the float bowl.
4. Invert the carburetor and check that the float
surface nearest the gasket is 1/8 ± 1/16 inch from
the gasket. Bend the float tab as required to pro-
duce this spacing.
NOTE: / / the carburetor u t i l i z e s an internally
spring loaded f u e l inlet valve, the float surface
should be 1/3 ± 1/16 inch from the gasket with
the f u l l weight of the float compressing the spring
in the needle. ' • • ,-. ;
v
5. Reassemble, install and test. v
6. See Figure 12.
B E N D T A B
T O A D J U S T
' G A S K E T T O F L O A T
D I M E N S I O N 17 8 I N C H
.,A?I3.-1.
F I G U R E I I . C A R B U R E T O R A D J U S T M E N T S F I G U R E 12. F L O A T L E V E L A D J U S T M E N T
15