I just had this problem on my duster. The spring broke and the valve was not working. I notice this when I starting smelling gas. It was boiling gas from the carb onto the exhaust manifold. I'm planning other things as far as intake/exhaust, so I drilled a hole in the counterweight and safety wired it open/off. It runs like a champ, actually better when hot. I live in Georgia, cold weather is not much of a problem for me, heat boiling gas is. I know some people will say this is wrong, but it works great for me.