Js550 Carb/Tuning Help

[Lynch]

Trying to figure out how to setup my carbs.

Been working on this budget js550 that I got for $180 and I just rebuilt the top end/did a bunch of stuff to the ski including paint/turf/new throttle etc. Right now she runs off of starter fluid but not off of gas. I've got the left nozzle hooked up to an empty slot on the gas tank and the middle one hooked up to the reserve slot on the gas tank with an inline fuel filter in the line.

Not sure what this extra nozzle on the right side of the carb is? is that return or something?

Pretty sure this carb is a bn44 right?





Here's what she looks like now.

 

[Spyder]

Yes its an bn 44 carb, stock on all 440 and 550's, I believe.

There is an extra inlet nozzle for the bn's for a rev limiter input. Hard to tell from pic's but it kind of looks like it's been removed. If it was there it's bolted to the side of the hull under the mount for the stock fuel filter, which also appears to be removed.

You should have a pulse line, fuel in line, return line (restricted if no rev limiter), and a rev limiter in (which can be capped if you don't want it or have it).

The rev limiter is done by tripping a solenoid based on a a voltage level at high rpms. The solenoid opens and lets fuel back into the carb inlet from the return line causing the ski to bog down.

 

[Jafaboy]

Just to be different, I'm going to say BN38, based on the 3 bolt flame arrestor and throttle cable attachment. Stock till '85?

 

[Lynch]

Just to be different, I'm going to say BN38, based on the 3 bolt flame arrestor and throttle cable attachment. Stock till '85?

sounds accurate when I google it. I'll try and take a look at the rev limiter later today.

 

[Spyder]

Yep, your right about the size being 38 instead of 44. Still operates the same with the rev limiter inlet though.

Just block it of but you’ll need to put some sort of restriction in the return line. Some people us a carb jet or others use a nylon spacer.

 

[Lynch]

What do I use to block it and where can I get the carb jet or nylon spacer for the fuel in?

 

[Lynch]

Is this the correct jet for the return line?

https://www.amazon.com/Mikuni-Pilot-N100-606-Super-Carburetor/dp/B003CJIASK

and just a .030 vacuum line restrictor from oreillys or something to block off that inlet?

 

[Spyder]

The inlet should be completely capped, Its there to pump extra fuel into the carb at high rpm to bog the ski down. Rubber cap and zip tie or something. The return line needs to be restricted to .030 to keep fuel from running directly back out to the gas tank instead of into the rest of the carb. The rev limiter circuit is the restrictor before it was removed.

 

[Lynch]

Pretty sure this carbs junk. Was opening them up and it looks like there is a screw broken off at the bottom. Gas was just dripping out of the bottom instead of going to the engine.

Should i go with a different carb or stick with thebn 38?

 

[Lynch]

Pic of broken studd

 

[Spyder]

I think the broken stud is the least of your problems, that thing is pretty crusty in there. That thing is going to get all plugged up.

A lot of people switch to the square body sbn carb but not really nessary unless your doing engine upgrades, they are a little easier to tune for upgrades. For all stock the stock bn carb works just fine. But that carb needs a serious cleaning. I’d consider just buying a clean used one one eBay.

 

[Spyder]

Another nice thing if switching to sbn carb is no messing around with cap for rev limiter inlet or restrictor in return line. There is no extra inlet and the return line restriction is built into the carb. However you have more tinkering with jet, needle, seat and spring sizes to get it tuned properly.

 

[Lynch]

Yeah I ordered another BN38. Guess I'm stuck riding the js300 til the new carb comes in.

 

[Spyder]

Good part about that is it shouldn't need much if any tuning, easy setup.

Good Luck!

 

[Lynch]

Yupp, I ordered a .030 mig tip for the return line and a cap for the rev limiter inlet. So hopefully it's in next week.

 

[Lynch]

Anyone have any good ideas for getting the old ass screws out of the start stop switch? Trying to install a kill switch. They are all stripped/stuck and drilling them out didn't seem to work.

 

[_evan]

You will probably break the kill switch if you drill the screws out. I would look for another? Are you doing lanyard mod??? I would only do that on a lake ski. I have been wrecked in surf because of those stupid things

 

[Lynch]

Yeah its for the lake. Trying to put a lanyard on it. Guess i dont really need it.

 

[Vermontjeepguy]

How do you know if you will need an intake spacer when switching from bn44 to sbn44? Certain years?

 

[Spyder]

All years with stock intake manifold, there are a few aftermarket intakes with the space built in but any stock intake manifold will not have the clearance for the fuel pump of the sbn carb.