Justera BN förgasare

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justeringar,installationer & reparationer till jetski

Justera BN förgasare

Inläggav Admin » 10 augusti 2020, 08:08

Hittade denna förklaring på pwc today hur man kan göra för att justera in BN förgasare som ofta
sitter på äldre kawasaki som JS440 och JS550 som jag testat och det funkade bra.

Men som han skriver du Måste ha allt annat reko inga läckage i packningar eller tätningar
i motorn etc då spelar det ingen roll hur du justerar och håll koll på stiften hela tiden!!!!
Även om du har möjlighet kolla även på toppen av kolvarna innan du kan slappna av
för att se hur du ligger till.

First off, you need to know the 86' to 91' JS550's top end was beyond service limit in the crate.
There was a defect in the pilot fuel screw (the bottom screw), and the main seals started leaking
after the customers first ride.

In fact, service departments that don't triage a JS440 & JS550 when they come in for a tune
service leads to ruined weekends, comebacks and dissatisfied customers.

If your 550 is in perfect condition, this will help, if not, continue this thread with why you need
to adjust your carb.

(1) Brand new spark plugs, engine warm, and secure on a trailer or tied to a dock.

(2) Always begin with the pilot fuel circuit and work up to the main. The pilot fuel circuit, the
low speed circuit continues to flow throughout the entire rpm range. The Hi speed screw setting
is the sum of the pilot + low + main jet circuits at wide open throttle.

Just for information: there are 3 types of low speed screws:
(i) (38mm round body Mikuni) simple low speed screw that provides fuel to the low speed bypass
holes (at the throttle butterfly), and controls the starting and low speed response.

(ii) 44mm round body Mikuni) Pilot fuel screw has a fuel source separate of the low speed screw.
It only meters fuel (sounds normal), and uses a low speed screw in conjunction with the pilot screw.

(iii) (Super BN & Keihin carbs) Pilot fuel air circuit. The fuel source of this circuit is the low speed jet,
and is different than (ii) because air from the low speed bypass holes (at the throttle butterfly) provide
air to mix with the fuel into the Pilot fuel air circuit.

The reason why I am going into this detail is to emphasize the importance of (ii); when the choke
isn't used, (ii) is the circuit solely responsible for starting the engine (and it was manufactured with a

(3) Begin by setting the low speed screw to 1 turn out (middle screw)

(4) Set the Pilot screw to 1 1/2 turns out (bottom screw), and the main screw to 1 ½ (top screw)

(5) With the engine running set the idle speed as low as you can. This is important for two reasons:
(a) The pilot & low speed screw settings are a balance between the idle speed, and the screw
settings. (b) Idle speed controls how fast the ski reacts to you falling off.

(6) Engine warm, running in the water, secure on a trailer or tied to a dock. (The engine must
have a load on it). Note: Be sure there aren’t any rocks near buy that can be sucked up into
the pump.

(7) Slowly turn the pilot screw inwards. The engine will start to gain rpm, then the rpm will drop,
and the engine will begin to die, or it will die. Now turn the pilot screw out 1/2 of a turn out.

(8) Restart the engine, test for starting, and low speed response. If the response is a little slow,
turn out the screw 1/8 of a turn. Now redo (5), (7) and (8).

(9) Adjust the hi speed screw for best rpm.

NOTE: Most mechanics will lean out the main too far when the ski is stationary. If the hi speed
screw is adjusted below ¾ of a turn out, it is too lean. Reset the hi speed screw to a rich 1 ½
and set it leaner by doing a few quick test rides. A test ride is about 50 yards at WOT. No more
than that.

Hope this helps, if you have any questions, continue this thread.

Bill M.
Site Admin
Inlägg: 93
Blev medlem: 31 januari 2009, 18:12

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