I had two of these, logged some 500 flights on them, nice airplane.
Futaba...you NEED 30% or more fuel. Need.
And...you need to tune the pipe properly. 350mm is just a starting point, you need to tune it for local conditions and fuel.
Awful lot of people got pretty mediocre performance by not tuning the pipe.
Do these things, or keep crashing the airplane.
Doubt if interference from a metal clevis had anything to do with anything, more likely the plane simply tip stalled.
Weight is not the issue, mine weighed some 66 ounces and took off fine.
Also, make sure you do not have the main gear installed backwards, it will put the mains too far backwards.