can any one help me im having a hell of a time with my 2.5 sometimes it runs great then 2 minits later it runs like junk also im geting bubbles in my gas line going to my carb and is there any other moters that will replace the 2.5 other than the siro .18 also i tried all the ajustments that i could thik of even went back to facktory settings many times but still get the same problums slugish at first then run ok for a bit the gets hot and shuts down also seems like it not as fast 2 speed also wont kick in thanks

As for an alternative motor for the 2.5.....I still stick with the O.S. .15 CV-RX with a hardcore racing head. Not quite as much power but reliability like no other. The most easy to tune motors I've ever owned!
As for the air bubbles. Do you use a fuel filter? If so take it off your problems should dissappear. Especially if it's a 2 piece filter with foam in the middle!

Good Luck,
CJK