Been working on it? OK, Ok I apologize just couldn.t resist. Something is wrong with this picture the engine will never run right with a loose carb and don,t start goobering things up with bull snot. If you have not damaged the carb boss the replacement pin may be the wrong one for a larger engine and cannot tight the carb before the thread stops the nut.

Also I have to ask is the rubber 'O' ring inplace around the carb boss and if this is a used engine could it have the wrong carb as a replacement?

This is the procedure for reinstalling a carb that uses a cinch pin:

1. The carb boss with the "O' ring around it is slipped into the engine boss for the carb and pushed right up to the 'O' ring.

2. Now with the needlevalve positioned cross way or slightly aft the palm of your hand is positioned over the carburator throat and your finger wrapped around the bottom of the engine. As you squeeze the carb is pushed down and pushes aginst the O ring and this is where the seal occurs.

3. With the freehand using only a properly fitting nut driver for the hex nut you now squeeze for all you are worth pushing into the 'O' ring the freehand tightens the cinch pins hex nut and this will actually pull that halve moon and the carbs boss tight aginst the crankcass holding everything very tight, there will be no play and the nut only needs to be lightly tightened.

Either you have a mismatch of parts, or missing parts or damaged the carbs boss where the cinch pin rides.

Agine get help at you local club or I can see much further pain in your future.

John