Brand New Mikuni Carburetor Questions

[csid]

I am working on a 1997 GSX. I purchased a brand new set of carburetors for it. The carbs, which are genuine Mikuni, are different than the carburetors I removed from my pwc. There are three fittings and a valve of some sort that the old carbs do not have. See the attached pictures.


The packaging was labeled BN40I-38-26 (MAG) and BN40I-38-27(PTO), my manual says the carb i need is a BN40i-38.

The packaging also listed the description as "CARB - BOMB 98' GSX,S"

My questions are:
Is this the right carb? Did the 1998 GSX use a 40mm carb?
If this is the right carb, what do i need to do with the "odd fittings 1-3?"?
How shall I proceed?

[Rotax787]

Re: Brand New Mikuni Carburetor Questions

That thing with the arrow with the ?????? on it is probley an accelrator pump which is a performence/starting thing. You will need to jet differently with it though. The 98 GSX did use and ac pump and the 97 did not.

Brett

[John Kubiak]

Re: Brand New Mikuni Carburetor Questions

98 GSX was a 947, it uses SBN 46i carbs which have a much larger capacity fuel pump. What you seem to have there are a set of 1997 SBN's for a 787 (800), they should work on you ski. Bill O will have more details on this.... Make sure that you hook up the accelerator pump properly, and also that you install the fuel restrictor on the supply line connecting the fuel chamber of the PTO carb to the accelerator pump.

[radiocontrolhead]

Re: Brand New Mikuni Carburetor Questions

so then he has the wrogn carbs

[John Kubiak]

Re: Brand New Mikuni Carburetor Questions

I am working on a 1997 GSX.

If the carbs fit a 1997 787 engine, there should be no reason they will not fit!

[csid]

Re: Brand New Mikuni Carburetor Questions

They will fit, they are the same casting and throat size as the carbs I took off. I am perplexed at the extra parts that are on this carburetor.

[Technical Support]

Re: Brand New Mikuni Carburetor Questions

Those are the right size, wrong model. That would work for an XP. You can get them to work, but I don't knwo the proper jetting - it won't be what you were stock, and you'll need small fuel line to attach the accellerator pump fittings.

[radiocontrolhead]

Re: Brand New Mikuni Carburetor Questions

bottom line, return them.

[John Kubiak]

Re: Brand New Mikuni Carburetor Questions

BOTTOM LINE: THEY WILL WORK AS LONG AS THEY ARE JETTED PROPERLY! The 1997 Sea-Doo was the first model from Bombardier that had the accelerator pump. The low speed jets were reduced to compensate for the addition of the accelerator pump. Use the carbs, but re-verify jetting before you run the ski. Get the appropriate size fuel line, and a tee-fitting and hook up the accelerator pump to the fittings at the throat of each carb.

[csid]

Re: Brand New Mikuni Carburetor Questions

Could someone help me with the jetting?
My 1997 GSX 787 is supposed to be:
Main Jet - 142.5 [both Adjusted to 1 +/- 1/4]
Pilot Jet - 87.0 [MAG adjusted 0 turns, PTO adjusted to 1/2]

Tech Support mentioned that these carbs are for an XP with the same engine size as my GSX.
The 1997 XP 787 was jetted at:
Main Jet - 142.5(MAG); 147.5(PTO) [both adjusted to 1-3/4 +/- 1/4]
Pilot Jet - 65.0 [both adjusted 0 turns]

Since John says only the low speed jets were reduced im thinking I should try
Main Jet - 142.5
Pilot Jet - 65


1. Turning the screws out will richen the mixture, True or False?
2. Any better advice on how to jet these carbs?
3. How shall I adjust the screws when I first install the carburetors
4. Where can I buy jets online?
5. Can anyone give me a little more information on what exactly the accelerator pump does (the item labeled ????? in the diagram), It appears to let more fuel in when the throttle hits a specific position, is that right? Why is this better/worse than using jets to add more fuel? (perhaps quicker response?)

Answers to any or all of the questions would be helpful. Thanks to everyone for their help so far.

[Bill O'Neal2]

Re: Brand New Mikuni Carburetor Questions

Dude, you got it backwards. Main jet adjusters are susposed to be closed to a quarter turn out. Pilots are the ones you open to at least 1 turn out or more to get it to accellerate.

Pilot jets are always smaller when you have accellerator pumps. They give it an extra squirt of fuel when you move the throttle lever.

Go with the oem jetting specs for YOUR motor, not somme other model.

[csid]

Re: Brand New Mikuni Carburetor Questions

Bill,
You told me that I should go with OEM jetting specs AND that pilot jets are always smaller when there is an accelerator pump. Not trying to be a pain in the *** here but my 1997 GSX carburetor did not come with an accelerator pump. The OEM pilot jet is a 87.0, my question is if i am to use a carburetor with an accelerator pump what size should my pilot jets be?

[Bill O'Neal2]

Re: Brand New Mikuni Carburetor Questions

You are the one who started talking about accellerator pumps.......

There is no such thing as an 87 pilot jet.
Your GSX oem jet sizes are 142.5 mains and 70 pilots, 1.5 N&S, according to the 1997 GSX parts manual.

The 1997 XP 787 engine has an accellerator pump. it uses 65 pilots, 142.5 mag, 147.5 pto, 95 gram spring with a 1.5 N&S.

[csid]

Re: Brand New Mikuni Carburetor Questions

bottom line, return them.

Starting to think you were right on this one...

[Bill O'Neal2]

Re: Brand New Mikuni Carburetor Questions

I think that retuning them is a stupid idea.
The later model carbs work great.
You have the right carbs for the accellerator model 787 engine. Use them.