Small Engines (Lawn Mowers, etc.): Stihl 028 AV, piston displacement, stihl 028

Question
QUESTION: Ran fine, then shutoff at high speed. Won't restart. Good spark. Checked the flywheel key and it's fine. Rebuilt carb and checked for clear exhaust.  Tried priming w/fuel and still won't start. Checked compression and it goes from about 20psi and builds up to 100 psi after about 6-8 pulls.  What am I missing??

Thanks!

ANSWER: Hello Chris::

>>The Compression Readings are Wrong.
>>The Compresion should Read Approximatley 100 PSI with the First Pull.
>>What Did the Cylinder and Piston Look like When you Pulled the Muffler and Cleaned/Checked the Exhaust Port?
>>Thanks.

Respectfully

John

>>PS: I am Allowed to Answer 10 Questions a Day. If you See I am Maxxed Out, then Try Submitting your Question at or Just After 8pm EST (US). My New Day Starts then. Comments and Ratings are Greatly Appreciated. Thanks.

Respectfully

John

---------- FOLLOW-UP ----------

QUESTION: John,

I think you are point on - Since I was using a compression gage witha 12-18" rubber hose I made the assumption the gradual pressure buildup on each stroke was due to the small piston displacement gradually filling the hose. I took the exhaust muffler back off and the sides of the piston and rings are scored and gouged.  Guess it's shot.  Do you think it's worth a replacement shortblock and what do you think is a reasonable cost for one/source?

Chris

Answer
Hello Chris:

>>I Suggest you Price the Jug/Cylinder, Piston and Any Other Parts that May be Required for Rebuilding this Unit and Price a New Unit.
>>Then you can Better Decide if you wish to Trash this Unit and Purchase a New One.
>>If the Cost of Rebuilding this Unit is At or Close to 1/2 the Price of a New Unit then a Rebuild is Not Out of the Question.
>>If the Cost of Rebuilding is Slightly Over 1/2 the Cost of a New Unit, then I Usually Suggest Purchasing a New Unit.
>>If you Hit a Snag or this Does Not Correct the Problem,  I am Here if You Require More Assistance. Hope this Helps. Let me Know What Happens, Please. As Always, May the All Mighty Bless You and Yours. Be Safe and Happy. Thanks.

Good Luck

Respectfully

John

PS: I am Allowed to Answer 10 Questions a Day. If you See I am Maxxed Out, then Try Submitting your Question at or Just After 8pm EST (US). My New Day Starts then. Comments and Ratings are Greatly Appreciated. Thanks.

Respectfully

John