1988 JS550 carb set-up

[Bill O'Neal]

Steve Strickland told me that someone used to make a spacer that goes between the clyinder and the manifold to move the oem manifold about 1/4 inch away from the clyinder for carb clearance. You might try that avenue.

Whatever you do, don't forget that restrictor in the return line. Without it, gasloine will just circulate and you will run lean on top end. A restrictor is noting more than a small round metal piece that fits tightly inside of the return line and has a .035 hole drilled into it. If the ski runs too rich, enlarge the hole size a little bit, after you get the jetting right.

You can make a restrictor very easily. Get a 1/4 inch rod, brass or aluminum, and cut it about 3/8ths of an inch long. I perfer to drill and tap it for a Mikuni main jet, but all you need is a hole the proper size so that it does not make the motor run fat (rich), but still maintains enough fuel pressure to feed the carb on top end.

[Ben Shiner]

Thanks bill, I'll look around and see if I can find those spacers. I have talked to a few other people, one of them said that a restrictor was built into the carb and I didn't need another, I got a diagram and it shows one too, do I need the restrictor in addition to the one in the carb?

[Bill O'Neal]

Ben,
You may need another restrictor. I always check to see that the built-in restrictor is really in there. Mikuni makes some carbs with it, and some without it, for different applications. It is located in the upper part where the returnline fitting is. It is a small hole in the casting (drilled) into the channel that lets the fuel out of the carb body. I think you will find it is quite large, about .100 or so.

Just be aware that you need some restriction to keep from running lean. The guy that told you it was in there, isn't the guy buying the new pistons if he's wrong.

[Ben Shiner]

Bill good point, and thank you, i'll definitely fut a safe-second restrictor in there.

Ben Shiner

[SubmarineAZ]

I used to have a 550 with similar mods to yours but my motor was ported. I ran the BCW manifold with a MIkuni SBN 44mm. I remember the jetting being about 120 low and 125 high with 2.5 needle/seat with a gold spring. That would be about 19psi pop off but I didn't have a guage at the time so I just went with the chart in the manual. I did not run a second restrictor in the return line. You may need to run richer or leaner jetting depending on the conditions where you do most of your skiing.
I also ran a stock carb from a 650 SJ on a 440 (high compression but not ported). These carbs differ from the Mikuni SBN because they were made to Yamaha specs. It worked fine but was overcarbed for that ski. I don't think I was using the BCW manifold for that application. I believe it was a later 550 intake manifold.
There should be plenty of those manifolds available if you check around. I have also heard Parks Perf has the hook up on just about anything 440/550
I would try and get an Ocean Pro flame arrestor used for your ski as you can get them cheap off Ebay and they don't require the adapter like K&N.
Hope this helps

[Ben Shiner]

I've been looking for the contact info for parks performance, but haven't been able to find it anywhere, can anyone help me out?

thanks