I have an 5hp craftsman snowblower that bought used. I got it home and it had no power. I brought it back and the guy, he changed to oil. It was almost grey and foamy. He made what looked like some carb adjustments and told me he increased the rpm's. Now I use the thing and it just doesnt seem to have the power it should. I have to keep on the 1st speed selection or it will take off. as far as reverse it is super slow. So slow that I dont use it. And it seems to make a high pitch whining sound. Any suggestions?