My SKi is "bogging" out?

I bought a 1995 wave venture. Purchased a new exhaust hose for it. (the heavy rubber one that goes from the manifold to the muffler). The old one was supposedly "dry rotted". When I got the ski, someone tried to put a PVC rigged up one in there. Blew that one out too. When I purchased the new, $90 exhaust hose, I questioned if maybe the exhaust and water going through it was way to hot and melting the rubber but the rubber was splitting. Well, the new one got about 12 hours on it and it too split. Anyone got any ideas about what the hell is going on with this ski? Is it running too hot?