hi
contact TOWER HOBBIES-OS has issued new parts for the engine for FREE-(thus recognizing a defect in design )-a remote needle valve and a new back plate-i spent two months trying to get this engine to run as it should the new parts solved the problem i run a 13/6 APC on my 60 ULTASPORT-OS WILL also redo you engines internals if they were damaged -mine were not REGARDS TONY