When dealing with a problematical engine I find it best not to choke or prime through the carb. In fact I might disconnect the fuel line altogether. Put a drop of fuel in the carb, but only enough to lubricate the shaft, and turn the prop over gently. Turn the prop until the piston closes the exhaust ports and then turn the engine over gently to ensure the cylinder isn't flooded (it shouldn't be). Back the comopression off as much as 3/4 turn. then start flicking smartly while advancing the compression. The engine shopuld fire, and run out a short burst. When it does this and does so consistently, you have established the compression setting. Attach the tubing and choke the fuel up to the carb, but no further. Re-prime against the piston wall again as before, and again back off the compression about 1/4 turn. Turn over to check, then flick smartly while advancing the compression. If the needle valve is in the ballpark, it should run. Always err on the side of lean on the needle - it is better to have it run a short burst than flood itself.

Tank position is important. At this stage, the top of the tank should be level with the spraybar.

Regarding head screws, they used to be BA threads, but at some point PAW went over to metric (about the same time that they went from metric to American in nomenclature - the logic escapes me). I think the crank thread is UNF. The heat treatment of the head screws can be important. If the bolts are soft, you will always be tightening them.