Edwin:

With 30-40 hours you probably need new piston/sleeve assemblies.

You might want to investigate the "Bru-Line" air filters, catch a lot of dust, engine lasts longer. They are small, easy to install/maintain, and cheap.

The R/C car boys have good air filters available, but the really effective ones are big and ugly.

I'm using Bru-line, pleased with them. One of my twins has a pair of Magnum 46 XL engines, five years old with ??? hours on them, Bru-line from new, they are still like new.

Try the head screws, might help.

Let me know.

The TT Engines at 30 hours, have probably lost all their powers.

Bill.