OK guys, here is my problem. 1 year ago I replaced the engine on my walkbehind. I replaced the old B&S engine with a new B&S engine, it is an Intek, 13.5 horsepower, I use the mower 2 times a week and it was fine until recently. The problem is I run the mower for about 1.5 hours and then it boggs down and finally cuts out, like it's out of gas. I then let it cool down for an hour and it will then run another 1.5 hours and does the same thing. I tried gasoline additive already. Any help would be appeciated. Thanks.