This is a recent issue that just started. Ran fine all spring till last weekend. 49' 8n 12v for stats of tractor, runs fine and then 10-15 mins into usage it will start to bog down and then eventually die within about 30 secs. I can pull choke in and out and it keeps it running enough to get it back to garage. Spark is fine on all 4 cylinders. Fuel I may have little bits of rust in tank and am afraid some may get into carb causing issue. Sometimes bogging down will clear itself and that's why I think this may be an issue. I have cleaned carb, and yesterday replaced metal fuel line over engine to a black fuel line with a inline filter so I can see fuel getting to carb. After this idea ran tractor and same issue happened. I will clean carb again and see how it goes. Ideas if problem persists? Thanks for any suggestions. I do t have a lot of technical mechanical speak so as much lehmans terms is better for me to understand.