Hi there. I'm new to this so bear with me. Recently purchased a 2nd hand JD 455 2WS, 22 HP Yannie. '99 model with 500 hours. Starts & goes well straight away - very happy going up hill & down dale. However after 30 minutes - 2 hours, it suddenly decides that going uphill is a little too hard & responds by almost, but not quite, cutting out. I'd say power loss is 90%. Engine never actually stalls. Seems the fuller the tank the longer it takes for the problem to start. Having PTO on or not makes no difference. Recovers briefly after 1 minute or so, but quickly loses power again. Because it can still move (very slowly), I head for level ground or downhill - presto, it fires up again & runs normally. Have changed fuel filter & drained tank. Cleaned uptake filter in tank as well. Could it be as simple as needing to loosen the fuel cap? I think it may be carby or fuel-line related, but would appreciate some input from the experts here, before I give up & go through the pain of carting it to be serviced. Cheers, Paul.