BS40 slow jets

tz375 · Post by **tz375** » Thu Jul 02, 2009 3:39 pm

Can anyone confirm which slow jets are used in BS40 carbs?

Regular VM use the VM22/210 which have 2 pairs of air bleed holes and a number of other small differences.

I suspect that the BS series may use BS30/96 slow jets.

Anyone know for sure, before I buy a whole pile of the wrong brass and go nuts trying to get them to work.

pjmcburney · Post by **pjmcburney** » Thu Jul 02, 2009 6:26 pm

Richard,

Not too sure what you mean by slow jets, unless you're referring to the air jets to help surging.

The OEM complete jet breakdown for the BS40's (Mikuni part numbers in italics) is as follows:

Mains - 110 / 107.5 / 110 - N102/221
Pilots - 45 (L 47.5) - BS30/96
Pilot screw - 3/4 turn (L 1/4 turn)
Needle - 4DN18-4 (L 4DN18-3)
Needle Jet - Z-0
Throttle Valve - 110 (L 120)
Float level - 27.6mm from the top of the float to the gasket surface without a gasket
Anti-surging air jets - 80 (L 90) - BS30/97

I'm using pilots with bleed holes in my L, it will hardly run if I use non-bleed hole pilots.

Hope this helps
Cheers
Paul

tz375 · Post by **tz375** » Thu Jul 02, 2009 10:33 pm

Thanks Paul,

I should have been more clear. The pilot jets I took out have two cross drilled holes and one additional cross drilled hole at 90 degrees. (6 bleed holes in total)

A stock Mikuni pilot jet as used in the VM carbs has two pairs of cross drilled bleed holes and that's the part number VM22/210. (8 bleed holes in total)

What I need to know is whether the stock pilot jet is SUDCO part number BS30/96 which looks like it may have less bleed holes.

Cheers

rngdng · Post by **rngdng** » Sun Jul 05, 2009 2:26 am

DON'T USE THE EIGHT HOLE PILOTS IN BS40s!!! I accidentally went the other way (six-holes in VM carbs). I flooded the crap out of the engine. You must use the six hole pilots in BS40s, or you'll be super lean.

Lane

tz375 · Post by **tz375** » Sun Jul 05, 2009 7:53 am

Thanks Lane,

I had stripped two sets of carbs and when I looked at the jets I had a mix of 6 and 8 and knew that wasn't right. I checked my boxes of jets and all the VM jets are 8 which I know to be right for those carbs.

I ordered a couple of sets of BS30/96 from our local carb supplier. When they arrive I'll be able to tell if they are the same as the stock 6 holes. If not I'll have to go OEM.

rngdng · Post by **rngdng** » Mon Jul 06, 2009 5:15 pm

They should be the same. OEM jets were Mikuni. Good luck.

Lane

tz375 · Post by **tz375** » Wed Jul 08, 2009 6:24 pm

Well it looks like the BS40 type 6 hole slow (pilot) jets are just BS30/96 jets available form any good jet supplier. Not only do they have 6 bleed holes versus 8 on VM jets but they are quite different.

I grabbed a couple of sizes because I hate going back time after time to get 3 jets.

Suzukidave · Post by **Suzukidave** » Wed Jul 08, 2009 9:48 pm

Whatcha tuning up Teaser ?

tz375 · Post by **tz375** » Wed Jul 08, 2009 11:50 pm

Err, Nuthin.

Honest mister...

I just started back on the Phat Trakka project. At the moment I'm modifying the seat that I got from Gordon Lamb a couple of years back.

What I'm planning is to rebuild the motor with a nice port job that all my calculations say will produce huge waves of power - OK so if I get lucky I won't have lost too much versus stock.

I want to run it on the dyno with stock pipes and new jets in the stock BS40 carbs, then I want to try that Strader 3 into 1 to document what it does to the top end and I'll need jets for that too.

After that there are a few other things I need to know, but I need to get it built first. The fork brace arrived and spokes for teh 3.00" rear rim are on order. Then I just have to finalize the port dimensions and build the motor and finish off those one or two small details.