Air mixture screw / Pilot Screw - BS34 Carbs

adi1974

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Hi guys, hope you can clarify for me.

I'm rebuilding the BS34 carbs on my XS and reading the tech section came across a few mentions of missing rubber washers on the air mix screws. I hit the shed and looked at mine, followed my Haynes manual which seems to call the 'air mixture screw' the 'pilot screw' (in the section for BS34 carbs).

-- A is that correct, are they the same piece, just different naming convention?
-- B - if that is the same thing, it shows in the diagram that there should be a washer and an o ring, on mine there is just a screw and a spring. - Should I therefore source the missing bits as per... http://heidentuning.com/p/28/2404/m...e-mixture-screw-with-spring-washer-and-o-ring ??
-- Or are they omitted on certain versions, such as a UK or Euro import (which mine is I think)?

Or have I got things mixed up?

On the upside, I also noted the fact that these carbs had rubber plugs that go in over the pilot jet, mine DOES have these so thats one less thing to worry about.

Thanks guys! Appreciate this forum enormously!
 
im not really understnding your question, but that link you posted is to the air/fuel mixture screw, i guess you could call it pilot screw. it is located on top of the carbs toward the engine. you dont need to replace the screw just need the washer and oring

and you do need a plug that covers the pilot jet which is in the bottom of the carb, other wise bike wont run very good

pm me and i can get you a mini rebuild kit which will include 2x washer and orings for the pilot screw and 2x plugs for the pilot jet. Also comes with oring for needle valve seat which are know to leak and the orings are all mikuni
 
Hi. Yeah I have the plugs for the pilot jet so no worries there.

My query was because the manual over here (UK) calls that part the pilot screw but I've only seen it referred to elsewhere as a air mixture screw. I wanted clarity that these parts are indeed the same and...

that there's no legit reason why my one (in the UK) doesnt have the washer and o'ring I suspect it should have?

I looked on Mikes and I can see you can get the cap, washer and o ring separately without buying the screw but Heiden (our nearest supplier in the UK) doesnt seem to do this option, it just looks like a complete screw kit.

I need a whole new needle valve / seat and oring assembly, mine were destroyed aswell. Thanks for the offer of a kit. I'm in the UK so it might be a problem with import / tax etc. unless you know otherwise. Cheers
 
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ps. I used some hardware store o-rings before to replace my needle valve o-rings and they just disintegrated. I guess there's therefore a need to use specific grade o'rings on these things exposed to fuel etc.
 
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you do need the washer oring for the bs34s the bs38s had the screw on the side and did not use orings for some reason

and i guess you can run the screw with thread sealer ?
yea you need special orings
 
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Apologies! Stripped it again and the washer and o-ring were stuck in the barrel. I fished them out. Looks like the o-ring is intact but quite flat, might need replacing. I noticed that the barrel of one side has a cut in it from the previous owner, I guess from when they removed the cap. Its deeper than the plastic seals I have, should I try and seal it? (attached image)
 
I reuse the washers even if they are rather flat. The top doesn't "have" to be sealed I like a bit of grease there so water doesn't get in and corrode the threads.
 
- - - Apologies! Stripped it again and the washer and o-ring were stuck in the barrel. I fished them out. Looks like the o-ring is intact but quite flat, might need replacing. I noticed that the barrel of one side has a cut in it from the previous owner, I guess from when they removed the cap. Its deeper than the plastic seals I have, should I try and seal it? (attached image)

Hi adi,
good that you found the washers and o-rings lurking down there.
I bent up a little hook out of a paperclip to fish mine out.
Is the red thing stuck into the needle hole a stock Euro-part or some plastic item that happened to fit in there?
If your XS was a US import the EPA Nazis legislated the needle be made non-adjustable by pressing a metal plug in there.
(And HTF am I going the clean the carbs with that there you EPA arsehole?)
Most likely that sawcut was part of a PO's plug removal technique.
But what fits in there perfectly is that hard rubber plug that seals off the slow running jet so if your red things are too garish for you, buy an extra pair of those carb plugs to keep the dirt out of the needle pockets.
 
Is that cut on both sides of the tower? Your PO may have been a bit aggressive with the drill when getting the plug out. Damaging the mix screw head. He may have just cut down through the tower to cut a new slot in the mix screw.
Leo
 
Thanks guys.

yeah the red thingy's came with it, they fit quite well and I sort of like them, they look a bit 'race' hah. Nice tip on the bungs though.

The saw mark is only on one tower, sounds like you've got a good theory there. Glad it doesnt need to be fully sealed. Thanks again guys
 
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