Ducati 900SS - Measuring the Float Level; Identification of Parts and Operation of Basic Circuits; The Float Circuit

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CARBURETOR
Identification of parts, and operation of basic circuits.
THE FL O AT CIR CU IT
The float circuit is o very important por t of th e sl ide· vo lve carburetor. It must accurately
maintain a sp
ec ific fuel level in the floor bowl or all times. Th e major components of the
floor circuit ore the float bowl . th e fl oa t volve -o nd·seor assembly, and the fl oat s. Many
slide·volve carb uretors use se p ara te. in de pendenl fl ools. and o float arm th ai connecls
1he m to 1h e fl oat volvo.
Because th e feed tubes for th e main. pilot, and storler circui ts exlend 1nto the fuel from
the main
ca rb uret or body, the fuel level in the flool bowl musl be high enough to reach
!h em. Bu t, even mo re significantly, th e fuel level ac tu ally affects h ow ri ch or leon the
engine
runs through its entire ra nge. The reason for th is goes bo ck to 1h e discussion of
1he vent ur i principle. parlicula rl y 1h e drop in vacu um 1ho1 occours in th e ven turi al low
air speeds. lithe fuel level is loo low, the decreased vacuum in 1he venturi cannel pull
enough fuel out of the fuel bowl and inlo the airstream
TIPS:
A l ow fu el level causes hard starling and o lean ai r fuel mi xtu re at low s peed s. Fuel
starvation may also result at high speeds. On the other hand. ,f the fuel level is too high.
too much
fuel is drown into the ventun, resulting 1n on overly nch mixture.
M EAS UR I NG THE FO AT L EVEL
Th is measurement is to ken fr om th e bo l lo m of the fl oa t. or the fl oat lever on so me mode l s.
to the carburetor-body gasket surface.
... NOTE: The float should be resting on, but not depressing, the spring- loaded
... float valve n ee dle.
The float lev el is adjusted by bending the tab on the float arm. Bend•ng the tab towa rd
the
needle valve raises the lloollevel, while bending the tab away from I he valve lowers
the float level. It should always be remembered !hot o h1gh float level res uhs in a l ow
fu el level. and o low fl oat level resul ts in o hi gh fu el leve l.
TIP S:
A fuellevellhot is too low usually shows up as o leon condition It may hove o reading
of low CO and low ·ta·normol HC. Under se vere candi lions. this co uld cause o lean
mis fi re.
In th e exhausl ga s analyzer show s 1hese re ad in gs . and the bike h esi to l es o ff idle. you
shou ld check the fuel level Th is is especially im po rt onl on models equipped wiih CV
corburelors.
The lower th e fuel level. the more resistance th e fuel hos to being drown into the venturi .
This is
who l causes leon readings on the exhousl gos analyzer.
A
fu el level thai is t oo high normally sho ws up as o rich r ead ing on th e exhaust gos
ana lyzer. Hi gh CO and normal-le- hi gh HC may be your r ea di ngs
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