I have an 021 with the non adjustable "H" jet and am thinking of replacing the jug / piston with one for an 025. I know I will have to replace the carb and crank seals , as far as I can tell everything else will work. If anyone can think of something else I will need to change, please speak up. I assume it will be as simple as tearing everything apart and swapping the pistons / jugs replacing the seals and carb swap am I right? This saw was given to me as a non runninng freebie and is in really good shape, runs well but I am a tinkerer and it would give me something to do on my days off. I would also be gaining about 1hp as far as I can tell:msp_smile:.