Stripped Butterfly Valve Screws

I'm rebuilding my carbs on a XJ550. I have 3 screws in two carbs that are not loosening.

I've tried to soak them in PB blaster. Is there another preferred penetrant? I've been hesitant to use carb cleaner on them because that will begin the break down process on the gaskets.

I've tried tapping them with a punch to loosen up the threads.

Thoughts on how to proceed?

I've been thinking about a screw extractor and\or drilling them out.

 

From the church of clean

https://www.xjbikes.com/forums/threads/in-the-church-of-clean.14692/

"On Mikuni carbs, this story goes from merely bad to worse: these screws are an absolute BEAST to remove, and it is very easy to destroy the screw heads as well as the throttle shaft threads while trying to remove them---if proper precautions are not taken. You will want to review the information in this forum thread before attempting removal:

http://xjbikes.com/forums/index.php?threads/8011"

The original poster mentions using a Dremel, but that's likely too aggressive and dangerous. I think a jewelers file should be the go to tool in this case, but I haven't tried it.

The JIS screw driver is an absolute must

 

Thanks for sharing that. I should have read the "church of clean" more carefully. Yep, I've been using JIS screw driver. Wish that I had them 10 years ago. Just to be clear, that document is about removing the tip\end of the screw? Were these screws "stamped" mushrooming the tips to prevent removal?

 

I think the choice is to "peen" them, a self locking fastener, or use Loctite. So yes, the tip / end of the screw on the XJ550 Mikuni carbs needs to be filed down and I can't advise on experience as my 750 Seca uses Hitachi carbs, which did not peen the throttle shaft screws.

 

If all the other screws on the butterfly came out, then I doubt they would from factory only peen three of them. You can always try to put some superglue on the tip of the screwdriver, hold it on the screw tight and wait for it to dry.

 

Over the decatdes I've had to removed screws from 100 year old guns that are stuck.
heat cycle sometimes helps
heat, cool, heat, cool.

You can use soldering iron (or soldering gun is better) if you like.
the expansion of the screw then subsequent cooling sometimes breaks the bond. Plus if someone used blue loctite, it will loosen in the heat.

 

WOOT! Got them off.

Used a hand impact driver with JIS bits. After a few taps they were lose. Thanks guys