Originally Posted by
Truckracer
All the DLE and similar engines use (2) double sealed bearings on the crank. It is very unusual to have all 4 seals fail. I have torn into some engines (not DLE) where a seal had failed on the rear bearing but that is all. Some engine companies remove the farthest rear seal next to the crank web as they thought the bearing would be better lubed with oil from the fuel than the grease packed in the sealed bearing. But the point is, it is very unusual to have an air leak through the crank bearings in current engines. Most of the time, I see leaks from loose cylinder hold down bolts or a damaged / warped / cracked reed block or carb spacer.
I'm thinking the problem with the engine in this thread is just a bad carb or pulse port that is somehow restricted.
I totally agree that nowadays leaking crank seals are very rare, though it can happen, and if it does will cause you a tuning nightmare if you don't know to look for it. It had been a long time since I encountered one, but I did run across one in a Zenoah last year. Many people don't understand that unlike wet sump four stroke engines, total crankcase sealing of a two stroke engine is imperative. Many years ago, many people changed the crank seals on two stroke race motorcycles after every race, but modern seals and oils are now much better. Nowadays a crank related leak on a new Chinese engine would more likely be the result of a factory defect; seal damaged on assembly, poor machining of the seal bore, etc., especially on the non-RCGF, non-DLE alphabet engines.
The OP stated that he substituted a known good carb on the engine with no change in behavior, and that he verified the pulse operation. That's why I am thinking possible vacuum leak. Using my pressure tester will find any leak, including the most common;: which is the cylinder base gasket or carb spacer as you stated. I recommend trying the ether or thick oil test first, as it is easier and quicker on a mounted and running engine. You do have to be careful with the ether so that the engine doesn't suck the ether into the carb throat and give you a false positive for a leak.
AV8TOR