Hi - I have been flying Thunder Tiger Pro .46s with OS #3 or #8 glowplugs for several years. I always buy new engines and break them in myself as I have purchased used engines and never been able to get them to run well. The only problem I have experienced with Thunder Tiger engines is sometimes they will want to start running in reverse, but that is the exception and not the rule. I have tried to fly on old fuel and that will cause problems. I have not tried Merlin glow plugs so I cannot comment on that, but I've had nothing but good luck flying these engines.

You mentioned you did not know if your engine had a ring washer or not. That could be a big problem, as there is a ring washer that fits between the carburator and the engine. There is also a gasket that sits between the muffler and the engine housing as well. Hope these tips will help. Here is a URL for an exploded view of the engine http://mms.tiger.tw/upload/2008-1/20081265128.pdf.