Bs34 stuck mixture screws - thread size

[madoc]

Basically the previous owner(s) had completely buggered the head on one of the mixture screws on my 1980 bs34 carbs.

I tried a few of the usual methods, lh drill an ultimately driving a small screwdriver into the chewed up remains. Nada.

Does anyone know the thread size of the mixture screw ? It's an M6 something ... But not any of the dies I have match. I'll get a first and bottom tap and hope I am centred enough to get a clean thread.

I think once the thread is sorted I can just tip the carb and shake out the needle bit...right ?

Why do people just do these things and then leave it ......


Thanks.

 

[gggGary]

Seems to be a M6 x .5 which looks like a std. metric fine thread.

This won't be found in your average tap and die set.
I matched the thread count to an m3x.5 I had in my T&D set.

 

[DogBunny]

This is just my opinion, but I've messed with a lot of buggered mixture screw holes, and you'll never get it right, and you don't need to because bodies are plentiful. If you were in the US I'd give you a guaranteed good body for $30.

 

[madoc]

This is just my opinion, but I've messed with a lot of buggered mixture screw holes, and you'll never get it right, and you don't need to because bodies are plentiful. If you were in the US I'd give you a guaranteed good body for $30.

Not the case over here. Neither cheap nor plentiful.
I guess I may yet end up trawling u.s. Ebay for a rh carb unless you'd entertain shipping abroad .. .?

I have had success doing this, but those carbs had the air screw flush and not stuffed down a "tunnel", like they are on this XS.

Is it possible to cut down the "tunnel", more level with the mixture screw ? This would make it easier to work with.
I assume the "tunnel" is only that long as it originally had a plug in it, to stop messing with the screws.

 

[DogBunny]

I see no reason why the "tunnel" can't be cut down.

I checked shipping costs. I think I can ship a completely stripped BS34 body for $17. I am almost positive that I can ship a body stripped except leaving the throttle shaft assembly intact for $20. First Class Mail International with tracking.

 

[madoc]

I see no reason why the "tunnel" can't be cut down.

I checked shipping costs. I think I can ship a completely stripped BS34 body for $17. I am almost positive that I can ship a body stripped except leaving the throttle shaft assembly intact for $20. First Class Mail International with tracking.

Thanks.
I ordered mixture screws (here by the weekend) and m6 x 0.5 taps (here by Weds).
I may attempt this at the weekend (cold and family dependant)

 

[gggGary]

Kind of late for you but post #7 in this thread may be helpful. I have removed several "no hope" idle screws this way. Including one where the guy I did it for bet I couldn't get it out.

 

[Huszarail]

John, Sent you a P.M. might help?

 

[madoc]

*update

I obtained a lead and bottom tap for m6 x 0.5 , which is right size.
Using the good side and its mixture screw to figure out the depth to drill to, I rigged up the carb on the pillar drill to get it all central.

Having the tunnel proved useful to ensure everything was perpendicular.

Drilled a 2mm lead and then a 5mm ( usually you'd go 5.5mm but I was stil wary about being off centre). I had already run the tap through the good side and knew how far to go, so it was a question of slow and careful.

I believe I have done it and I was lucky to do so.
It remains to be seen if everything is ok in actual use.

I did find one side without rubber or washer however

 

[gggGary]

That's great! Will just throw out even though the deed is done: Putting a sleeve on the drill/taps so the "tunnel" bore keeps them centered would be useful.

 

[DogBunny]

Good job. To check the quality of your work, do the following: Assemble mix screw, o-ring, washer and spring, and screw mix screw gently all the way in until it bottoms out. You should be able to see the tip of the mix screw protruding into the carb bore about 1 millimeter -- compare to your other carb. Now, take the mix screw all the way out, and see if the tip still looks straight and un-damaged. Shine a flashlight down the mix screw hole, look at the orifice at the bottom of the hole, compare to your other carb.