The problem I am having is that both tires are all over the place. Toe in, toe out, one and both. I have replaced all parts except for steering wheel and column and the same thing is happening. There is no adjustment. What am I missing? HELP!

Having some trouble with my rider mower. I bought it used from a guy and it started up great and ran well. I cut about 3 times with it, then it would cut for about 20 minutes and then just stop, not even run rough but just shut down. I changed out the fuel lines, sprayed the carb, topped off the oil and it cut a few more times with no problems. It is now doing it again, if it sits for 20-30 minutes I can cut again for another 5-10 minutes then it shuts down. I adjusted the valves and it fired right up, I thought that was the problem, it ran great for about another 10 minutes then shut down and now will not start at all. I cleaned the carb thoroughly, wire through all the holes, new float gaskets, made sure the needle valve was in good condition. I operated the needle valve with the bowl off and the float was working correctly. The fuel solenoid operates correctly. I put everything back together and it cranks but will not start. I have a brand new spark plug with great spark. I checked to make sure I had good flow from the tank, and again checked the needle valve operation. If I place my hand over the intake with the choke on it will start to fire and I can get it to fire over for about 15 seconds while holding my hand there. This seems to me like it is running way too lean, so again I checked the needle valve to make sure it wasn't sticking, ran some wire through the jets again and everyting is clean and clear. I am at a loss now, I don't know where to go from here. Can anyone give any suggestions? It is a Nikki Carburetor, and there doesn't seem to be any adjustments that can be made on it. It seems like I have a carb problem though. The last time I ran my hand over the intake to get it to fire, I had a real loud backfire after it shut down. :wall: