Mixture screw adjustment

[Gary pope]

OK let me start off by saying I know my JetSki is not a Sea-Doo, I have been having some issues getting some confirmation with regards to the high-speed and low-speed adjustment screws on the side of the carburetor that I just rebuilt. The JetSki is a 95 Mastercraft kraze wet jet with the Yamaha 701 motor in it. I ordered the manual for the 95 Yamaha motors in it to get the specifications on the carburetor, but there is nothing about the high-speed and low-speed mixture screws. I guess my question is does anybody have any information on these adjustment screws and how many turns in they are supposed to be? I do have experience and Sea-Doos, just not these Mastercrafts I ordered the manual for the 95 Yamaha motors in it to get the specifications on the carburetor, but there is nothing about the high-speed and low-speed mixture screws. I guess my question is does anybody have any information on these adjustment screws and how many turns in they are supposed to be? I do have experience and Sea-Doos, just not these Mastercraft .
Here is what the carburetor looks like.

And here is what I found in the manual

 

[mikidymac]

The standard is 1-1/2 turns out from all the way in on the high and low. Start there are see how it runs.

 

[Gary pope]

I thought on the high they should be all the way in, no backing out? Can you tell what model carb it is? I did find the adjustments in the manual but I really don’t know what model it is, like wb 700, wrs700....etc

 

[etemplet]

I'd start of 1-1/4 turns out on low speed and all the way in on the high speed.

 

[mikidymac]

No, only Seadoo closed the high speed. Like I said it’s a Super BN 44 and try the 1-1/2 turns out. Worst case it’s a little rich.

 

[etemplet]

You'd find out pretty quick the high speed needed more fuel. LOL You're right though pretty much everything starts out about 1-1/2 turns. I go 1-1/4.

 

[Sportster-2001-951C-Stock]

The low speed screw is the idle mixture screw, adjust for an idle that doesn't load or make for hard rich 10 minute restarts yet leaves enough fuel in the crankcase for off-idle acceleration. 1.5 from lightly seated is usually close, 1/8 turn can make a difference, twist them and see if idle is affected if not there's sumting wong.

The HS screws for this type watercraft are usually fully closed lightly onto the seat and opening it should cost you WOT RPM. No effect on low speed operation but once in the water try opening and see to be sure. Running too lean (hesitation is a sign of being lean) melts pistons If it's supposed to be open (say 1/2 turn or more) and it's closed (too lean) the engine won't accelerate during a hole shot, I call this hesitation when the motor falls on it's face and stalls but too rich the motor keeps running just at low RPM and 4-strokes (fires only about every other compression stroke) runs but costs WOT RPM.

Better to be slightly too rich than too lean at WOT, there's a fine kneepoint where power and detonation damage (you can't hear the detonation but you can feel hesitation and assume detonation is occurring or close) are balanced.

I probably just said more than is necessary....

 

[mikidymac]

I don’t understand why there is an issue here. The Yamaha engine has the high at 1-1/2. It is only the Seadoo ‘s that close the high speed screw. Just set the damn thing at 1-1/2 and see how the plugs look and how it feels at wot.

 

[Sportster-2001-951C-Stock]

I don’t understand why there is an issue here. The Yamaha engine has the high at 1-1/2. It is only the Seadoo ‘s that close the high speed screw. Just set the damn thing at 1-1/2 and see how the plugs look and how it feels at wot.

Wrong tone. There's a very good reason Seadoo calibrates that way.

 

[Sportster-2001-951C-Stock]

You'd find out pretty quick the high speed needed more fuel.

Exactly.

What is the motor, what is the carb, Super BN 38 or 44, bla-bla-bla...

 

[Gary pope]

Motor is the Yamaha 701, carb I believe is a 44. It would help out if someone out there could help me out with identifying the carb model number itself.. like RA700, RA700A....etc...

 

[Sportster-2001-951C-Stock]

It's not easy finding specs on that Mastercraft ski to really nail down the carb details but, maybe give these guys a call? Ask for Dennis.

www dot wetjetparts dot com

Home

 

[Sportster-2001-951C-Stock]

Quick search I found these specs for a Yamaha ski with the 701, single carb setup apparently used either type 44 or 38 carb.

SBN44
120 low speed jet orifice
115 high speed jet orifice
1.5 N/S Diameter of seat orifice
115Gram metering spring
1 turn out on low
3/4 turn out on high

SBN38 is
65 low
107.5 high
2.0N/S
118G spring
1 turn out low
1.5 turn out high

So say for instance your carb has the 115 high speed jet and 120 low speed jet, that would be Yamahaha's tune and the carb would be the SBN44.

 

[mikidymac]

Like I said way back in post #2 Yamaha opens the high speed screw and this is a Yamaha 701, not a seadoo with the high closed. Put the thing at 1 turn out and go run it, discussing it to death won't help. Good luck.