At idle, your accelerator pump arm should have NO play in it. It must start moving the instant the throttle starts moving. Look down the carb with a flashlight to confirm there is actually fuel being squirted into the carb, you can do this with the engine turned off. That 8.5 power valve may need to be replaced with a 9.5 or even a 10.5. A vacuum gauge will help here or just try the 10.5 to see if it helps. If the squirter is too big it can be confirmed with someone watching the exhaust for a puff of black smoke when you "blip" the throttle.