I put a 40 in a Sig Cadet Jr. They only take a 15-25. I always use a 25. The 40 would flip the airplane invert in a slow pass if you punched the throttle hard. I*t would also take it straight up vertical. But 4 ounce of fuel don't go far in a 40. It did not take me long to remove and put a 25 back in. I did end up putting a ST 34 in though. That was not bad heck of a climb rate. Still had to watch how fast you advanced the throttle at low and slow. Even with a 25, easing the throttle forward not a bad ideal if you really slow.
Ken