Will a SBN-38 Carb fit my 1990 Seadoo SP?

[hollis_61]

Greetings,

I have just joined this forum so please excuse any breach in etiquette. I am the original owner of a 1990 Seadoo Sp and want to replace the original BN-38 single carb (pn 270500054). Will a SBN-38 with integrated fuel pump fit? What is a good part number and where is the best place to purchase this carb? Will I need any special adapter plate?

Thanks for any help.

Cheers,
Steve

 

[RodInEscondido]

I am playing with the same idea on my 89 and 90 SP stable.

According to the experts I have been in contact with, physically it should be ok.

What I have found is that it is a little more difficult to find the newer bn38 from a single-carb installation and if you get a dual-carb setup with the intent of using just one of the carbs you will find, and I am still playing around for a solution, but will kinda hijack your thread to share some info/questions.

Note the dual-carb setups, one is stamped "mag" and the other is stamped "pto".

In the dual-carb setup, the one with the fuel pump has pretty much free-flow output on the return side that feeds the input on the other carb, the non-fuel pump carb has a much smaller return flow orifice, presumably so you maintain the same fuel pressure on both carbs. These orifice dimensions are described in SeaDoo specifications documents but seem to vary between models and I have not sat down to study it further yet.

My theory, being set up on a bench-run setting, is that you should be able to use the non-fuel-pump carb in a single-carb config using the external fuel pump that is in place now. This of course based on the sub-theory that the external and carb-mounted fuel pumps are designed to supply the same fuel pressure/flow.

My second theory is that you should be able to bypass the external fuel pump and use the fuel pump on the carb in a single-carb config. The problem that I am looking at resolving is what size orifice do I need in the return line to insure proper fuel pressure. In my limited experience and perusing stuff here it appears that newer skis use this method where the output lines from both carbs go to a "Y" fitting then to the return line to the fuel tank and little hints and logic indicate that the flow restriction in the output line(s) to maintain fuel pressure will either be in both carbs or in the return line back to the fuel tank.

Have I screwed with your mind enough or maybe even helped?

Calling experts ... help us out here ... or tell me that I should just go back out on my porch with a cold one and continue my rain cloud watch.

 

[Dr Honda]

YES !!!!!


And it will get rid of the dumb external fuel pump. AND... best of all... I've personally done it. So... there is a thread on the proper jetting too. I'll have to find it for you.

 

[Dr Honda]

OK... here's the info......


If anyone else has an old ski, and wants to swap on a SBN... (it gets rid of the external fuel pump) the jetting I'm using is:

130 main
67.5 pilot
1.5 needle @ 35 psi pop-off
1.25 low
.25 high





And... here's the restoration I did on a 1990 Si.

http://www.seadooforum.com/showthread.php?25985-New-project-Give-me-your-input

 

[RodInEscondido]

I knew my ignorance and questions would shake out one of the experts. We got one of the best! Thanks much for the info and great to see you back Doc.

My remaining question is how you addressed the return line orifice issue? If you used a carb from a single-carb installation the issue is self-resolved. If, as I am attempting, you are using the fuel-pump carb from a dual-carb setup, what would be the orifice size needed in the return line to insure proper fuel pressure because the fuel output side on this carb (research indicates this is probably dependent on year and application)?

 

[Dr Honda]

I used a carb that was meant as a single. But... you may have to paly with return restriction. but...... off the top of my head... 0.040 may work. but depending on the flow of the system... you may need something smaller.

The easy solution would be to put a pump on the PTO carb, and go.

 

[RodInEscondido]

I will continue my experiments when I get my 580 set up for bench test and start another thread with results.

Again Doc, thanx for info.

hollis ... ya got some good mileage on your first post. I would normally say sorry for hijacking your thread, but I think we both benefited.

have fun on your project and feel free to post with pictures, progress, questions

 

[hollis_61]

Thanks guys, this is what I needed. I will purchase the SBN-38 carb tomorrow and get it installed.

Cheers,
Steve