removing stubborn carb. butterfly valve

Finally back to working on the Maxim. I'm breaking down the hitachi carbs to rebuild.

As is the way with Murphy's law, I've got everything taken apart... except the last screw on one of the butterfly valves.

I've done it all right - I took a file to the bottom of the screw in case it was peened. I'm using a JIS impact screwdriver, and it worked like butter on the rest.. but this one wallowed out. Even used a little liquid wrench to see if it helped.

Soooo... what are the tricks for removing this last screw without scratching up anything else in there?

thanks!

 

Do you have a left-handed drill bit?
If not, get one (or better yet, a set).

Set the left-handed drill bit ot it, and the screw will typically walk out.
I usually use a smallish drill to put a good dimple in the head, and follow up with a larger drill so it has a good chance of catching on the edge of the dimple.

If it does not walk out then you'll have to drill to the minimum diamter of the screw threads to eliminate the screw (this is best handled by a machine shop if you have no experience with the process).