One of the problems with the Evolution ( not EVO ) engine used in the PTS is that the needles WILL "walk" causing it do do exactly as "[AKA]StraferX" said.

This is not obvious and tends to occur as the engine heats up in flight.

I've seen it drive grown men to drink...

There is nothing otherwise wrong with the engine per-se.

You need to first REMOVE those #($&%^ limiters.

Then pull the clips out and unscrew the HS needle completely.

Carefully, preferably with a micro-brush, add a bit of lock-tite just to the threads of the HS needle.

Re-install, then bend the clip to make sure that it puts as much pressure as possible on the detents.

Likewise do the same with the LS needle.

Done correctly the engine will run as as good as, well an O.S. engine !