The thunder tiger 15 ( new series in red box ) is a good sport motor that does not need to be run on a bladder. Runs fine as is. With a few modifications this motor will perform as well as any 15 with a muffler attached and will last longer. As with all motors there is a weak point . If you try and turn over the motor in a flooded condition you risk breaking the crankshaft. Liquid will not compress. I have tested this motor with different props, fuels, intake timing, and compression ratios. No abnormal wear was noted untill the rpms exceeded 23000 rpm. Even then only minor wear on the crankshaft bushing was found. This condition however allowed the motor to run even better. Make sure you run castor oil / syn with at least 18% oil content. The most effective way to increase power without taking the motor apart is to open the carb to .205". This alone increases the rpm 1000 rpm. Removing the baffle and opening the muffler to .250 will yield another 500 rpm but you loose the back presssure needed for a constant run. This however can be overcome by modifing the internals and increasing the rpm another 2500 rpm.