Strato spit back / 576xp

[Jimmy in NC]

Working on a 576xp. Saw is pretty high hours and acted like an air leak. Flywheel side up and it accelerates. Rotate back to normal and it almost always dies.


Passes pressure and vac check fine with OEM testing flanges.

Did a flywheel side seal anyways... bearing is fine in there. No change.

Popped the top end and evidence of being very hot on the flywheel side. Looks like lite scoring hours ago through some lines in the jug... piston looks fine.

Since I had a set it got new OEM rings. No change.

I do notice quite a bit of spit back through the strato ports. Piston also shows signs of rocking with wear below the intake and exhaust; machine marks elsewhere on the piston.

Could the piston just be worn out? Saws runs fine with good power other than it won't idle and tip over. Will run fine off idle.

Swapped carbs off another 576xp and still has an issue rolling side to side.. but now seems to die with a low rpm flywheel up. Two junk carbs? Original carb pressure tests fine.

 

[Jimmy in NC]

Look at the blow by line from the top of the piston from the rear handle. Strange to me that it has a distinct line on the "cool" side of the cylinder. I am at wits end.. and baffled.

 

[beaglebriar]

The PTO side bearing pocket is usually the weak link on these. Strange that it passes a leak down test with those symptoms.

 

[Jimmy in NC]

s soon as he called me I figured air leak. I'll pull the PTO seal tomorrow or the next day as time allows... crank does not move at all in there though. The amount of strato spit back is also very strange to me. Normal intake spit back I understand... the strato should be 'dry' unless it's picking up spit back from sloppy piston.

 

[beaglebriar]

Dukes piston is like ten bucks. It’s worth a shot and you wouldn’t be out much.

 

[Jimmy in NC]

Well I admit defeat...

I have installed a NEW OEM piston and cylinder, two different OEM carbs, non-modded muffler, new OEM seals, new fuel pickup filter, and a new plug just because.

For now I am going to say its a lousy intake setup that's pooling or something. Bearings are fine.