Manifold/Exhaust problem for 1997 GTI

[henryr7]

After about a week after purchasing a used 97 GTI it was out on the water when the engine stopped. When we started working on it we eventually figured out that when the exhaust manifold is removed the engine starts up fine. When the exhaust Manifold pipe is on and in place like it should be it doesn’t start. The pipe is just an empty pipe that the exhaust runs through so we are stuck as what to do next we’ve checked it isn’t blocked with anything and the compression on the plugs is normal as well (130-140). My dad and I are new to PWCs is there something we are missing here has anyone seen this problem before? The Jet ski doesn’t run with anything connected past the manifold. With nothing hooked up it runs great or with the shop vac hose in the exhaust pipe.