FUEL
SYSTEM
CARBURETOR (GASOLINE)
Downdraft a n d s i d e d r a f t c a r b u r e t o r s a r e u s e d on the two c y l i n d e r e n g i n e s . C a r b u r e t o r s a r e
a d j u s t e d
i n
the f a c t o r y , a n d u n d e r n o r m a l c o n d i t i o n s , r e q u i r e no f u r t h e r a d j u s t m e n t u n l e s s one of the
following conditions is noted: B e f o r e r e a d j u s t i n g c a r b u r e t o r , c h e c k condition of a i r c l e a n e r - - a n " o v e r -
r i c h " m i x t u r e i s often c a u s e d by a poorly s e r v i c e d , clogged a i r c l e a n e r e l e m e n t . A l s o c h e c k f o r l e a k -
ing intake manifold o r p o o r ignition which could a l s o c a u s e s o m e of the conditions.
CONDITION
POSSIBLE; CAUSE/PROBABLE
REMEDY
A .
B l a c k , sooty e x h a u s t s m o k e , engine
A.
M i x t u r e too r i c h
-
r e a d j u s t m a i n f u e l needle.
sluggish.
B .
Engine m i s s e s a n d b a c k f i r e s a t high s p e e d .
B.
M i x t u r e too l e a n
-
r e a d j u s t m a i n f u e l needle.
C.
Engine s t a r t s , s p u t t e r s a n d d i e s u n d e r
C.
M i x t u r e too l e a n
-
t u r n m a i n f u e l a d j u s t m e n t
cold w e a t h e r s t a r t i n g .
1 / 4
t u r n c o u n t e r c l o c k w i s e .
D.
Engine r u n s r o u g h o r s t a l l s a t idle s p e e d .
D.
Idle s p e e d too
l o w
o r i m p r o p e r idle a d j u s t -
m e n t
-
r e a d j u s t s p e e d then idle fuel needle
i f
needed.
Two t y p e s of s i d e d r a f t c a r b u r e t o r s a r e u s e d . One type h a s e x t e r n a l a d j u s t m e n t s f o r Main F u e l
a n d Idle F u e l .
The o t h e r i s a fixed m a i n jet type which h a s a n e x t e r n a l a d j u s t m e n t f o r the Idle Fuel
needle only. On fixed j e t c a r b u r e t o r s , m a i n fuel a d j u s t m e n t i s p o s s i b l e only by changing t o a d i s c h a r g e
j e t of d i f f e r e n t s i z e . If a n engine with fixed jet c a r b u r e t o r is to be o p e r a t e d a t high a l t i t u d e s (above
6000 f e e t ) the s t a n d a r d j e t should be r e p l a c e d by a s p e c i a l 6000' jet. Another s p e c i a l j e t is a v a i l a b l e
f o r o p e r a t i n g a t 1 2 , 0 0 0 f e e t above s e a l e v e l . S e e p a r t s m a n u a l f o r c o r r e c t p a r t n u m b e r s .
C a r b u r e t o r A d j u s t m e n t : Maximum p o w e r a n d efficiency a r e p o s s i b l e only with p r o p e r c a r b u r e t i o n .
I m p r o p e r c a r b u r e t o r a d j u s t m e n t c a n l e a d t o o v e r h e a t i n g , fouled s p a r k plug, e x c e s s i v e valve w e a r and
o t h e r p r o b l e m s . Do not neglect c a r b u r e t o r if a n y of the above p r o b l e m s p e r s i s t . The following a d j u s t -
m e n t p r o c e d u r e is f o r s i d e d r a f t and d o w n d r a f t gasoline c a r b u r e t o r s - - s e e Special F u e l S y s t e m Section
f o r p r o c e d u r e on o t h e r types of c a r b u r e t o r s .
STEP
1
-
Stop engine a n d c a r e f u l l y t u r n Main F u e l a n d Idle F u e l Needle adjusting s c r e w s a l l the way
in ( c l o c k w i s e d i r e c t i o n ) until they bottom gently - - DO
NOT
FORCE SCREWS a s t h i s will
d a m a g e the needle valves.
l U L t
t U t L
I D L E FUEL
ADJUSTMENT
TURNS OPEN]
ADJUSTMENT
(2
TURNS OPEN)
ADJUSTMENT
FIGURE
4-1
ADJUSTMENTS, TYPICAL SIDEDRAFT
FIGURE 4 - 2
--
ADJUSTMENTS, F I X E D MAIN J E T CARBURETOR
CARBURETOR (K482. K532
)