Saving Old Seagulls

Stripping down AMAL 46n carb to clean for fitting to Century, cannot unscrew float chamber lid, have tried penetrating oil and heat but don't want to use too much force to break it, at the moment soaking it in petrol, any other suggestion?
Bob H

I am renovating a 1958 Century and your web site is invaluable. However in the forums I keep getting "You do not have the required permissions to view the files attached to this post"
How do I rectify this?