I wouldn't say the MOST likely cause of lack of compression is worn crankshaft oil seals. Statistically the most likely cause of a lack of compression is piston/barrel scoring due to insufficient lubrication.
Easiest thing to do is simply remove the exhaust from the front of the saw and peer in to the exhaust exit hole in the cylinder and inspect the condition of the piston. ANY marks and evidence of scoring indicate poor compression and would require a new piston, rings and quite possibly a barrel.
If you have a compression tester, then don't bothe taking the exhaust off, just remove the spark plug and do a compression test. Anything between 130-160 is fine. Below 100psi is junk.
pleasant
August 2012
2 stroke engines need three things to start & run - fuel, spark, and compression (priimary AND secondary).
If you have fuel and sparks, but no start, then the most likely cause is lack of primary (crankcase) compression, due to worn crankshaft oil seals. Only answer for this is a complete engine stripdown, in most cases. Sometimes, the seals can be replaced from outside - not sure about this particular model.
L & H screws should be set 1 1/2 turns out from fully closed, as a starting point. This should allow you to start it.
Phil Saunders
May 2012
take spark plug out and get it redhot with a gas ring or blow lamp.refit carefully and quickly and try starting it
Fingers
April 2012
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