I have a T2500 (4-stroke) trimmer which has been upgraded to 2510. It runs great, but it is a devil to start. I choke it and prime it and it takes 4-8 pulls when cold. After it warms up, if you turn it off you can crank it with one pull. However, it it sits a few minutes then it won't start unless I prime it, choke it and give it full throttle. It taks 5-10 pulls to start it under this scenario. It is almost as if the gas is draining back out. When the trimmer is running, it runs and idles great. The plug is new and works good in another T2510 I own. Also, I usually operate the timmer at almost full throttle and I have tried turning the unit upside down and shaking it before I turn it off to make sure no oil has accumulated (suggested by factory rep). One other thing I noticed is that the rope seems harder to pull when it is hard to start. It is as if the decompression valve is not working properly. Any suggestions are appreciated.