300/440/550 Is tuning a BN carb like tuning a SBN carb?

[ger87410]

1989 js550 stock carb. I think it's a BN44.

I know how to tune a SBN 44. Is tuning a BN the same process?

 

[Polish jet pilot]

More or less. You have 3 screws. Remember however that SBN has interchangeable jets. BN does not have this option. If look on the side close to the screws of the carb you will see "H", "L" and "P". This are for high, low and pilot just
dont turn more than 1/4 turn at a time...


Have fun

 

[SUPERJET-113]

Knights of the round pump unite!!

BN's suck azz. I hated those carbs back in the day. If you can, sell it and get a SBN. I sold a 44 BN a few years back and only got $20 for it.

 

[orangefinger]

Get a new needle and seat they are always junk in jused bn"s..

 

[jetskimechanic]

To answer your question they tune different than a SBN for the set up but for the BN, The Pilot adjsuter is for the idel only and then the low speed adjuster is for up to 1/4 - 1/2 throttle and then the main jet which I drill out to .040 is for the 1/2 -3/4 and then the high speed adjuster is for the 3/4 to full throttle... Always start with the pilot and go up from there as each circuit still feeds the carb so going the other way will effect the results...

 

[dirkdiggler]

how many turns out on the pilot adjuster is a good place to start?

Does anyone know what size Needle/seat & spring came stock on a 1990 550sx??

 

[WILKEY]

my bud has a carb like this on his 550..... we just put the coffman pipe on there... should anything be changed in the carb? or will tuning it right work?
one more question.... which is the pilot screw the one at the very top?

 

[waxhead]

Tuning a round pump is like whacking your balls with a hammer

They will both drive you insane with pain