Carb Screw Upgrade

[chris711]

Hi, I am cleaning my carbs and changing the screws from JIS to Allens (as per 5Twins thread on this).
My understanding is that JIS and Allens have the same thread and pitch, however, when I screw my Allens in the carb body they go so far then tighten up to stop.
I am not keen on breaking through this as it does not feel right? The original JIS seems to travel through without any problem.
I have tested on all holes and both carbs. All the same. (This is the M4 x 12/14mm's for the carb float housing).
Any advise would be appreciated, anyone else had similar?
Many thanks...

 

[Jim]

Gotta thread pitch gauge? I suspect it's the wrong threads on your new screws.

 

[chris711]

Threads seem to match when held next to each other side by side... This is the spec from the supplier. I understand both JIS and Metric 0.7mm.

The M4 x 12mm Full Thread Cap Head Screws (DIN 912) - Stainless Steel (A2) has the following features:

• 2mm Hexagon Depth (P)
• DIN 912 Manufacturing Standard
• 12mm Length (L)
• Yes Fully Threaded
• Stainless Steel (A2) Material
• Stainless Steel (A2) Material Specification
• 0.7mm Screw Thread Pitch
• Natural Finish
• M4 (4mm) Thread Size
• +0/-0.22mm Head Diameter (D) Tolerance
• +0/-0.18mm Head Length (H) Tolerance
• 3mm Socket Size (J)
• 4mm Head Length [Max] (H)
• 7mm Head Diameter [Max] (D)

 

[Jim]

Try a little cutting oil and see if they'll work their way in then?
Run 'em in 'till they bind, unscrew 'em about a thread or so and retighten. Repeat until they finally seat/bottom out.

 

[gggGary]

An old cheaters trick was replace stripped screws with an SAE screw that was just a bit bigger
Tread carefully, hate to see you end up with 1/4 20 float bowl screws.

 

[Jim]

An old cheaters trick was replace stripped screws with an SAE screw that was just a bit bigger
Tread carefully, hate to see you end up with 1/4 20 float bowl screws.

If you do push it up to the next size (M5's).... for all practical purposes, an SAE 10-32 and M5 are interchangeable.
Just an FYI...

 

[chris711]

OK, thanks for your replies... I will give that a go...

 

[5twins]

I always apply anti-seize to these, especially since they're stainless going into aluminum alloy. For some reason, I find the threads on stainless fasteners seem to be "sharper" and more easily strip holes in alloy. I also only use a stubby screwdriver or one of these thumb wheel bit holders to tighten these carb screws. This guards against over-tightening them .....