I have a nice 2007 yam 15 hp 2 stroke, I have checked compression with 2 different testers. both say 125 top & bottom. I have strong spark jumps a good 7/16 to 1/2 on three different spark checkers. I replaced the carb on it from my dads 15 yam which is identical to mine (but his runs very well) made no difference on how mine runs (bad). mine runs as if it is running on one cylinder at WOT. it starts well and idles fine but when I try to power up it has no power at all. I also switched power packs from my dads that also made no difference, I looked at the reeds they look fine, I'm lost. What should I check next? good carb,,good spark,,good compression,, All the hoses seem ok, this is a very clean motor. pls help. thanks