Have had my 84 Nissan 720 for a while and recently ran into a problem. The exhaust smells very rich, and the motor loses revs when the throttle is pressed a certain amount, about a third of the way. Any point before or after and it revs fine, but at all times it runs very rough. I have checked the fuel flow to carb and the bowl level, both are fine. My next thought was to check vacuum. I did notice that the intake does not seat well and the gasket between it and the carb is deteriorating. What do you guys think?