Su thread enquiry

[5portsrock]

Hi, Does anyone know what thread the suction cup retaining screws are? Part number JFZ1394 in burlen catalogues. Thanks.

[Alex]

BA I'd imagine, but I don't know the size.

[Peter Laidler]

Suction cup.....? Haven't got a Burlen catalogue. Do you mean the dash-pots? I think that they're UNC...., quite a coarse thread. I'll go and check...

Added later.... just checked on an old carb body. If it is the dash-pot retaining screws then they're 10-24 UNC(coarse). Same screws as the fuel bowl screws

[5portsrock]

Great stuff. Thanks for the replies

[Peter Laidler]

I was hoping that someone would come on board and 'correct' my thread sizing - 10-24 UNC because when I inserted that size tap - a brand new one, I felt that It was a tad tight....., like I was cleaning/clearing out the thread a bit. But enough to ask myself if I had guessed it wrong. So maybe not.

[iain1967s]

3/16 BSW [Whitworth]

Same 24 TPI pitch as your tap Peter, but 55° thread form and slightly smaller OD at 0.1875”

However the differences are only about +5 degrees angle and +2.5 thou OD, so 10-24 UNC should be functionally equivalent given the tolerances of a worn alloy carb body…

[Peter Laidler]

Appreciate that explanation Iain. Never even considered Whit! Strange choice of thread in the 60's. Regards

[iain1967s]

http://www.minispares.com/product/Classic/JZX1394.aspx

[Desmodromic]

Here are some of the notes I put together some time back

H series carbs

Dashpot to body screw: 3/16” BSW (½” long, brass or plated steel slotted cheese head)
Fast idle lever to body screw: 0BA (5.1mm tap drill)
Throttle stop and fast idle screws: 4BA (3mm tap drill)
‘W’ clamp, and throttle return spring clamp screws: 4BA
Vacuum take off (lower corner): ¼” BSF
Float bowl to body: 7/16” BSF
Main Jet retaining screw/nut to body: ½” BSP
Float bowl lid retaining screw/nut: ¼” BSF
Float bowl lid inlet: 3/8” BSP
Butterfly retaining screws: 1/8” Whitworth (¼” long)

HS Series carbs

Dashpot to body screw: 3/16” BSW
Float chamber lid retaining screw: 3/16” BSW
Throttle stop and fast idle screws: 4BA
Float chamber to body mounting bolt:
Butterfly retaining screws: 1/8” Whitworth

[mini63]

Useful thread to get this info better understood.
just for fun, SU put 1/4BSF threads in the base of the non-mini fitted AUA66 fuel fumps.