BS34 Air Screw O-Ring Size?

Does anyone know definitively what the correct o-ring size is for the air screws on BS34 carbs?

I've seen the question asked here a few times, but have yet to see a definitive answer.

I tried using the smallest size that comes in the Harbor Freight Nitrile Metric O-Ring kit (they are labeled as "006", and they appear to have the correct I.D., but are too fat to fit down the hole. Would a standard "005" size fit, or are they a non-standard size?

The 006 number you refer to is the position number within the kit. Metric orings use the Rxx system where the xx is the size such as R05. The company I buy orings from doesn't use the metric number system and lists the orings by size and I just can't remember the size off the top of my head... the sizes are in fractions like 3.9 x 1.2mm so it makes them real hard to recall... sorry.

Thanks, George. That's what I originally thought too until I saw o-ring sizing charts like this one:

www.allorings.com/size_cross_reference_framed.htm

...where all the standard sizes are referenced by a -00x number. Since their "-006" size looks pretty close to the "006" in the kit, I assumed that's what they were referring to.

If you can possibly find that information on the size of the o-rings you order, I'd sure appreciate it.

Thanks again.

Here's link that's probably worthless to you. :lol:

But, the minions are searching.

Part# per chance?


Sudco O-rings

Patton wrote:

Here's link that's probably worthless to you. :lol:

But, the minions are searching.

Part# per chance?


Sudco O-rings

Oh, Patton. I feel we're so close to the answer now! If only I could find the MIKUNI part number for that o-ring! All I can find is the Kawi part number (16038-022). Anyone have a cross reference to the Mikuni number?

Post edited by: Skyman, at: 2007/08/29 17:20

Okay, so there are two o-rings referenced on this chart that indicate they are for Pilot Air Screws. The one that is 2.5mm I.D. x 1.55mm looks like it could be the right size, but I am thown off by the "Mikuni Reference" number "VM14/75". Does this mean it is for their "VM" series carbs?

The other one may be too thin, I'm thinking. But I certainly could be wrong. Its dimensions are 2.7mm I.D. x 1.13mm.

I mic'd the diameter of the groove on the air screw where the o-ring goes, and it measured 2.99mm. The outside of the screw shaft measures 5mm. So if I stretched the 2.7mm over the 2.99mm groove will the 1.13 thickness be enough to form a good seal around the screw?

Skyman wrote:

... 2.5mm I.D. x 1.55mm looks like it could be the right size...diameter of the groove on the air screw where the o-ring goes...measured 2.99mm. The outside of the screw shaft measures 5mm. So if I stretched the 2.7mm over the 2.99mm groove will the 1.13 thickness be enough to form a good seal around the screw?

For comparison, what is thickness of Harbor Freight's 006 that's too fat to fit down the hole?

PS -- also, what is diameter of hole? And what is outside diameter of HF's 006?

Post edited by: Patton, at: 2007/08/29 18:27

Post edited by: Patton, at: 2007/08/29 18:29

Meanwhile, might consider e-mailing Sudco about availability of o-rings for air screws on BS34 carbs.

(Can't hurt to ask )

Am loving this site's ability to allow possibly helping find pilot screw o-rings for a carb I've never even seen. :woohoo:

Patton wrote:

Meanwhile, might consider e-mailing Sudco about availability of o-rings for air screws on BS34 carbs.

(Can't hurt to ask )

Thanks for the suggestion, Patton.

I called Sudco, and they said that they cannot get o-rings for BS34 carbs. He said that is an "OEM Product" only. He said the o-rings listed in their catalog are not for the BS34s. He was also not able to give me the specs for the OEM rings.

del

Skyman wrote:

... called Sudco, and they said that they cannot get o-rings for BS34 carbs. He said that is an "OEM Product" only. He said the o-rings listed in their catalog are not for the BS34s. He was also not able to give me the specs for the OEM rings. :

Excellent effort in calling, and likely a truthful answer, but illogical to believe Sudco used some wierd one-off specially sized pilot air screw o-rings for a certain limited production oem Mikuni Kaw carb. So we suspect the correct size o-rings are out there somewhere. But I've enjoyed being wrong lots of times

"OEM product only" --- Are the correct o-rings available though the friendly local Kaw dealer? What Kaw model(s) was/were eqipped with BS34's? Has dealer inquiry been made? Is dealer saying "NLA"? (which gets us back to square one).

If Sudco doesn't have it and doesn't have the specs, and dealer doesn't have it, I don't know who would.

So let's proceed from square one with measurement of the hole diameter wherein the screw if fitted.

Knowing it's out there somewhere, not ready to give up, yet! :laugh:

Am guessing but want to believe the Mikuni BS34 carb pilot air screw o-ring serves the sole function of preventing intrusion of outside air around the screw past the threads and into the internal carb circuit through a threaded hole wherein the pilot air screw fits into the carb body. So that if the pilot screw threads were themselves "air-proof," the o-ring would actually not be necessary. (Is this reasoning process valid in the current application??) . Because, as a last resort, there may be options available without using an o-ring. And is an exploded parts diagram of the BS34 carb readily available?

Enjoying the challenge.

Post edited by: Patton, at: 2007/08/29 20:14

Patton wrote:

"OEM product only" --- Are the correct o-rings available though the friendly local Kaw dealer? What Kaw model was eqipped with BS34's? Has dealer inquiry been made? Is dealer saying "NLA"? (which gets us back to square one).

Yes, they are available from the dealer. But silly me, as a matter of principle, I don't want to pay $3.50 ea for a tiny o-ring when I can get a bag of 200 for $10.00 and share them with all my friends at KZR. :whistle: