Ditto UncleHo, However if you must use a stromberg, use the early 1-3/32". (Definately no larger than the 1-5/32". (Venturi size is stamped on the side of the main body). If you are using the later type (therefor larger), I suggest you prise out the power valve plunger from the carby top and check the plunger piston, these have a small plug, like a welsh plug inserted into the top of the piston. These plugs commonly fall out, I usually solder them in when replacing them. The loose plug allows the vacuum to escape and subsequently the plunger drops down under spring tension opening the power valve. The power valve in these later carby's is far to large for the 2.25 requirements giving a rich mixture and even allowing the engine to run with the main jat blocked. there are several other possabilities, difficult to diagnose via internet. Check that the power valve is not leaking (remove and vacuum test), Blocked air bleed hole or tube, damaged or incorrectly installed emulsion tube (these sometimes fall out when main jet removed). Float level etc.
Hope this may be of some help, I strongly suggest you stick with the original carby, they can usually be sorted out.
Regards Andy.