1988 JS550 carb set-up

[Ben Shiner]

I'm building an 88 JS550 piston port motor, but I'm a little uneasy with how to do the intitial carb set-up. Here's what it has. Cometic Copper Head gasket, JetSport High compression head (the domes look about 66-75% the size of the stock head), stock mikuni 44 BN carb, Accel flame arrestor(maybe), diabled Rev-limit valve, Westcoast "Works" pipe, Mariner Exhaust mainfold, Wiseco pistons (stock size). I would like to know if I will need to re-jet my carb, if so how do I go about that, and what size jets do I use. Or if I can leave it stock what would be a conservative initial setting for it? It has High, mid, and low speed screws.

thanks again,
ben Shiner

[Bryan Glynn]

Well, the pipe and flame arestor are going to necessitate a rejet, going much fatter, but I don't know to what size jets. If no one gives you an answer, you'll have to pickup the next few sizes up in jets and start rich, get to the 4-stroking point then work your way down.

[Bill O'Neal]

Brian,
Those old "round bodies" Mikuni's with 3 adjusters are a ***** to get right. The third adjuster is a pilot circuit, which is about 3 10 thousandths in diameter inside of the carb body, and usually clogged up. Rarely can they be tuned correctly. The hot ticket is to dump that carb for a later model SBN 44mm Mikuni.

[Ben Shiner]

Okay, I'm picking up a Westcoat RED-E-MADE Mikuni 44mm SUPER BN, with a 140 High speed jet, 120 low speed jet. Can you give me an idea of where to go from here? I'm really lost on the issue of jetting and tuning, and I don't want to have to pay to have my boat professionally tuned. Thanks.

[Bill O'Neal]

It may run a bit rich with 140 and 120's. I haven't done one in several years on a 550. I don't know right off exactly what I used back then. Maybe someone else can chime in here ? If not, I'll find out for you. I have a buddy nicknamed "550"...

[steve802cc]

Will a 44mm SBN carb fit on a 88 JS550? I had heard the fuel pump portion of the carb would hit the cylinder.
Steve802cc

[Ben Shiner]

I hope it will fit, I honestly don't know, I've heard of others putting SBN's on, but no on an 88, I guess I'll see when it gets here.

[Bill O'Neal]

I'm no expert on 550's but I believe the mid eighties models had 38mm carbs, then in the late eighties they went to the 44mm carbs. 44's have a wider bolt pattern than 38's. These carbs were refered to as "round bodies" because the fuel pumps were round shaped. In the early nineties, Mikuni made an upgraded 38&44mm Square bodied carb, Known as the Super BN.

If the fuel pump should hit the clyinder, you could use the flat fuel pump blockoff plate that came on the SBN twin carbs, were one carb had a fuel pump and the other didn't. Then you mount a remote pump on the ski to feed the fuel to the carb.

[Ben Shiner]

Great, thank you. I have just a few more questions. Will I be safe to start testing my ski with the super BN and the jets I said it comes with? Does anyone else out there have some ideas for jetting the carb? And where can i get the fuel pump block off plate and a reliable fuel pump. My ski has a rev-limiter valve that I am disabling. the valve, when activated, takes the fuel from the return line and pumps it down the throat of the carb, are there any precautions I need to take when removing this valve, or can I just hook the return line from the card straight to the tank? Thanks again!

Ben Shiner

[Bill O'Neal]

A friend just emailed me saying that the 88 550 came with a round body 44. He also stated that Beach City Watercraft sells a maniflod that allows the use of a SBN on that motor. I assume that with the new manifold, you won't need the remote pump nor the blockoff plate. When you remove your return line rev limiter, you should install a restrictor into the return line to keep the fuel pressure normalized.
He also said that BCW has jetting specs for all of the Kawasaki models and differnt exhaust systems that people use on them. They are located in Long Beach California.

On my 650, with the SBN, I used a 120 low speed jet and a 115 high speed jet. I suspect that you should try something like 120L, 120H for starters.

Allways be very careful when changing carbs or jets. Start out rich, then lean it down.

[Ben Shiner]

Do you have Beach City Watercraft's contact info, or do you know of anyone who could supply the parts? also do you know how I could fabricate a return line restrictor?

Thanks,
Ben Shiner

[Bill O'Neal]

Ben,
I called information and got 562 432 6550 for BCW.

You don't need to fabricate a restrictor. Ask for one with the manifold.

[cameron da river rat]

i can tell you how to re-jet(drill out) your old carburetor but know nothing of the square body carbs fitting on the 550.

the 44mm round body does not have replaceable jets, they are pressed in like freeze plugs and have a pre-set hole drilled in them. i know how to modify the stock carbs and what the screw settings should be, but i think it's too late for that.

you are better off with the more powerfull square body carb anyway [img]graemlins/uts.gif[/img] . much easier to adjust and modify w/replaceable jets in all sizes and less screws to adjust. the old round bodies are a pain in the @$$!

[Ben Shiner]

I called Beach City Watersports, they no longer manufacture the manifold for the SBN, they are thinking to maybe in the future, so I will go with the block off plate and a remote fuel pump. The man I talked to said to use a 107.5 High, a 75 low and a 2.0 needle and seat with about 15-18 lbs of pop off with a K&N style flame arrestor, and the westcoast pipe and mariner exhaust manifold. Does that sound good to y'all? Let me know what you think!

[Bill O'Neal]

Ben,
Before you do that, I'd check with someone more familiar with this swap than I am to be sure it will fit using the oem manifold, if you haven't allready.
Also, there may be some of those manifolds around still. I believe Ocean Pro, PJS and possibly Westcoast, and L&S made some too. Are you familiar with Parks Performance ? He carries alot of jetski parts.

I will probably go by Steve Strickland's house later today (used to own L&S). I will ask about who made what and the jetting for the 44mm carb.

It usually never hurts to get a second opinion.