Yamaha 2006 150 txr 2 stroke. hard to start,needs to choke even after warm up, engine dies if idleing for 2 to3 min. will not reach W.O.T. 4,200 rpm. New spark plugs seem to be gas fouled after one hour of running. New fuel water filter , checked filter on motor clean,NPF. Primer bulb stays firm. Run stabill and 93 OX fuel. could be fuel pump diaphram? Mechanic for 45 years..HAAA.; ALso what is the last year Yamaha txr 150 were brought to the USA? Purchases in 2008 Motor was new but is 2006 on S/N.?