Hello Jim, I have a 2500 on a 22 pound 4star 120 and it is using a 18x9 prop that seems to be the max for this engine as it truly does not like to wind up but does pu;ll a larger prop. I have all of the big tigres up to the 6000 and I do like the 2500. I have switched to the OS 7d carb on some and on others the stock carb works fine. Why? I do not know and I suspect that no one does as I see so many differant ways that it is very confusing.. I disagree with Bax as my 2500 loves a rich idle and if I lean it then it does exactly what your's does Quits on advancing a throttle. I have mine where it smokes all the time on full throttle and it ticks over on idle and advances like a electric motor.
On my 3000's (I have 3) the suggestion is to use a cline or iron bay regulator with crank pressure as they love fuel withthe tigre carb. If you use muffler as a source the pressure is to low and flow of fuel is low. With crank pressure you get 12 PSI and the regulator drops it to 11/2 PSI and the flow is perfect, when you shut the engine off all flow stops so it is great for an inverted install. I understand that6 the chinese tigre carns are better but have not tried any so cannot state for sure but I have done all of the above and since I know what a low slow and dead engine can do to a plane, I insist on dead reliable engines and this is what makes my tigres reliable. I like the 2500 better than the 2300 or the 2000 but it is not as powerful as the 3250 which figures and the 3250 is my favorite.