Stihl FS94 low compresion

[mowandgo]

Had this machine since November 2014 so its 22 months old. I love the high power, light weight & useability but its a bitch to start & will not hold revs. Compresion test said 60 psi. I took the barrel & piston off and its clean with no obvios wear. I run good green stihl oil through it. I just expect it to last longer the unit is still in very good condition. It has been used almost every working day but its only 22 months old.

 

Any one else had poor show from new Stihls?

[spudulike]

Is that one pull or 5-7 pulls holding the throttle open?

[mowandgo]

its holding throttle open and pulling many times. I also left compresion tester for 10 minutes to see if it would hold presure and it did. I also use the compresion tester on a bunch of engines allways seems acruate. Is this engine end of the road or could I get piston & rings at senciable cost & run again?

[Johny Walker]

i do believe its a carb issue ,its a none diafram type, iv got 2, 1,under the work bench were it got kicked

[spudulike]

A healthy engine, even a small one will pull 140-170psi, some manage higher but the 60 you are getting means that there is a serious issue as a seized engine often pulls more.

 

Check the bore for wear, check the rings for wear (especially the ends), make sure they are free in their grooves, make sure the exhaust port is free of carbon, check the end gap on the rings is 7-15 thou, make sure the piston is a good fit in the bore, make sure the crown isn't cracked or holed. There must be a serious issue somewhere unless this machine has some sort of strange decomp on it!

[Johny Walker]

A healthy engine, even a small one will pull 140-170psi, some manage higher but the 60 you are getting means that there is a serious issue as a seized engine often pulls more.

 

Check the bore for wear, check the rings for wear (especially the ends), make sure they are free in their grooves, make sure the exhaust port is free of carbon, check the end gap on the rings is 7-15 thou, make sure the piston is a good fit in the bore, make sure the crown isn't cracked or holed. There must be a serious issue somewhere unless this machine has some sort of strange decomp on it!

 

they run fine for so long then go down hill very fast + they dont feel like a high compression engine from new not as hogh as the 4s engine