Question about carb tuning

[ShAkEdOwN]

I am running a Mikuni 44 BN w/ mariner manifold and westcoast pipe w/ jetsport manifold on a '90 550. I can't seem to get it tuned right, can anybody help me?:banghead:

 

[SUPERJET-113]

Have you went completely through the carb? Taken out the jets and checked to see if they are plugged or slightly plugged? Making sure the needle and seat are in good condtion? Cleaned basket filters? Good fuel pump diaphram?

If you have something wrong or worn out inside the carb, it will never tune right.
So you say you have a BN? You meaning a round pump or a SBN(square pump)?

 

[Island750]

It is a round pump BN.

 

[aqua]

there is a manual on mikunis website explaining just about everything you would need to know about the super bn carbs. it has a real good section on carb tuning that help me out. i do not know how much you know about carb tuning but maybe it could help you as well. it is on this site under manuals

http://www.mikuni.com/fs-carburetor.html

 

[Matt_E]

That Mikuni manual is for the SBN - the OP has the old style BN carb. They have little in common.

 

[Jr.]

The key to tuning that carb is to have a good needle & seat. And to have a restrictor jet in the return line with a .040 hole drilled in it. Keep the restrictor as close to the exit on the carb as possible.

The next is to start tuning on the bottom & work your way up. There are 3 adj screws. The pilot & Idle adj are needed to be set first. then Low & Highs.................. I havn't tuned an old Round in a while, but if you take your time, you should be ok.

ski ya, Paul

 

[ShAkEdOwN]

Should the restrictor jet be in there originally?

 

[cookerq62]

ShAkEdOwN,
There was a restrictor originaly in the return line. I think it was a rev limiter or something like that. The sbn's have a built in restrictor. It allows the fuel pump to build pressure. I have seen a few sbn's that had the return nipple filled with solder or jb weld then drilled out. I'm not sure if thats kosher but it ran like a champ.

 

[waxhead]

the round pump is not as efficent as the square ethier
so you normally find pop off has to be set lower
i used to have awestcoast reddy made one
i was glad to see it go ( in the bin)

 

[ShAkEdOwN]

This is a BN round body, does the restrictor need to be drilled or is it ready to rock?

 

[ShAkEdOwN]

Do you guys think I'm better off getting the SBN?

 

[waxhead]

yes

 

[QJS]

A Super BN will not fit unless you have a spacer to get the carb away from the head.
Chris.

 

[waxhead]

well there you go
my 550 experience you could write on an postage stamp

 

[QJS]

LOL @ Wax, they do work well if you be bothered to do it though.
Chris.

 

[waxhead]

yeah they should
i have had a r/b on a 650sx( my first ski)
i found them so hard to get right
but that was 14 years ago i am sure i would have more of a chance now
but when i put the s bn on it was alot easier

 

[ShAkEdOwN]

I have an aftermarket intake would that make a diff on the clearance?

 

[QJS]

Unlikely but I have just found a couple of the spacers we made up all those years ago, you can have them for free if you pay the postage I might even have some jetting written down in my notes.
Chris.

 

[ShAkEdOwN]

Sweet, let me get back to ya on that. I am not the one who would have to pay for the new carb.

 

[cookerq62]

QJS,
Does the spacer move the carb out like a reed spacer???