Robert,

You must be running the Gen. 1 engine with the aluminum pan. Most people on this site say their Ryobi's came with a 7.5mm carb which leads me to believe that they all are using the first generation of engine. Gen. 2 has a plastic engine pan and a 9mm WYL. The stock jet is a 35. I put in a 46 from another carb but that is too much fuel. Also, I've been told that the WT456 carb is a dual needle number that came on the Gen. 1 engines and will work.

Do you get a surging in your idle and top end rpm? Mine fluctuates up to 300 rpm with the stock carb when idling and full throttle. My guess is that the removal of intake and exhaust restrictions have excessively leaned the mixtures. I'm thinking the adjustable needles on the WT456 carb should stop that.

Keep us posted on any new findings with this engine. A friend of mine has a boring bar and honing machine and I may try to punch it out if possible.