The first Magnum GP 40's were made by Thunder Tiger. I was always told that the Tower 40 was also. I know you can swap parts in the three engines.

More often than not, people speak more highly of this engine than they do the OS 40 LA.

You may want to remove the carb from the engine. Disassemble and clean it inside and out. It may possibly be assembled with the barrel upside down? Check and see if this is possible.

I had one a few years back and it always ran perfect with the screw half way accross the hole. It never gave any trouble so I never worked on it.

Enjoy

Jim