Fuel System; Engine Overheating; Engine Preignition; Engine Detonation - Polaris 1999 Sportsman 400 Service Manual

46
68 . On 199 9-on mode ls, the eng ine shou ld lose
s park and stop. If the engine continues to run , the
sw itch (C, Figure ( 6 ) is faulty and mu st be re-
p laced, Re fer to Cha pter Eleven.
7. Install the throt tle contro l cov er.
FUE L SYSTEM
Do no t automa tically assum e that the carburet or
is at fault when the engine do es no t ru n properly.
Whil e fuel sys tem problems are not unc ommon,
carbureto r adj ustme nt is se ldo m the answ er. In
many cases, adju stment wi ll only co mpound the
problem by making the eng ine run worse.
Begin fue l sys tem tro ubleshooti ng wit h the fue l
ta nk and wo rk throu gh the sys tem, reservi ng the
carbure tor as the final poin t. Mos t fuel sys tem prob-
lems result from an empty fue l tank, a plugg ed fue l
filter or fue l valve, fuel pu mp failure or old fue l,
Fue l system troubleshoo ting is co vered thoroughly
und er
Engine Is Difficult To Start, Poor Idle Speed
Performance
and
Poor Medium- and High-Speed
Perfo rmance
in this chapter.
ENG[NE OVERHEAT[NG
Engine overhea ting is a serious problem that ca n
qui ckl y ca use engin e seizure and da mage. T he fol-
lowing section groups
five main systems with
prob-
able causes that can ca use eng ine ov er heating.
I .
Ignition system:
a,
Inco rrect
spark
plug gap.
b. Incorrect spa rk plug heat range (C hapter
Three ).
c. Defecti ve COl un it/incorrec t ign itio n timing.
2. Engine compression system:
a. Cy linder head gas ket leakage.
b. Heavy carbo n buildu p in co mbust ion cham-
be r.
3. Engine cooling system:
a. Improper sp ar k plug heat range.
b. Cooling sys tem ma lfunction.
c. Clogged rad iator.
d. Thermostat stuck closed .
e. Worn or damaged radiato r cap.
f
Fan sw itc h malfunct ion ,
g. Dam aged cooling fan blad es.
h. C
logg ed
or
blocked coolant pas sages in radia-
tor, hoses or eng ine .
i. Oi
l level low.
CHA PTER T W O
J. O il not ci rcu lating properl y.
k. Valves lea king.
I.
Dragging bra kes .
111 .
Clutch/drive belt slippage.
11 .
Heavy ca rbo n bu ildup in combustion cham-
ber.
4. Fuel system:
a. C logged air filter element.
b. Carbu retor fue l leve l too low.
c. Incorrect ca rbure to r adj ustment or j etting.
d . Loose ca rbureto r hose cla mps.
e. Leaking or dam aged ca rburetor-to-a ir filter
hou sin g air boot.
f.
Inco rrect air/fuel m ixture.
5. Engine load ----<: hcck
for :
a. Draggi ng brakc(s).
b. Damaged
d rive tra in components.
c. Slippi ng cl utch/d rive belt.
d. Eng ine oil level too hig h.
ENG[NE
Preignition
Preignition is the prem ature burning
of fue l and
is
cause d by hot spots in the comb ustion cham ber.
G lowi ng depos its
in the combustio n chamber, inad-
eq uate cool ing or an ove rheate d spark p lug ca n all
cause preignitio n.
This is
first
noticed
as a
power
loss but wi ll eventua lly result in damage to the in-
tern al parts of the eng ine because ofhig her comhus-
tion cha mber temperatu res.
Dernna tion
Com mo nly ca lled spark
orfuet knock
. detonation
is the vio lent explosion of fuel in the co mb ustio n