I own a stihl f544 trimmer and it has begun to give me problems. It has provided years of trouble free service but this season it has been running sluggish. It has trouble cutting grass and is hard to start. It seems like the motor is bogging down or missing. I have replaced the spark plug and adjusted the carb. and nothing helps. I would like to fix it but if it continues to give me problems I am going to buy a new one. If it comes down to that I have been considering a 4 storke model, what opinions do you have on these. It seems like they would be easier to operate and more reliable starting. Any comments that you have are greatly appreciated. Thanks.