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

Carefully hold it with a pair of grips, with the float bowl held in a vice, nipped up with soft jaws.it should pop open.