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I'm working on a Poulan Pro PR5020 with Ruixing H225-50 carb. Owner said that shortly after purchase and cutting down 2 trees, saw would stop immediately after start. Some data from my investigation:
-pressure tested fuel line, no leak
-carb fuel in holds pressure
-fuel filter clean (did not replace)
-cleaned carb. diaphragms and gaskets are clean/flexible and appear to be in good shape
-compression of ~125psi
-holds pressure and vacuum when I seal intake/exhaust
-piston ring is not stuck
-as per photo, piston (as seen from exhaust) has vertical scoring. I can run a ballpoint pen across this and feel the scores
-As I received the saw, low needle was set to 1 1/4 turns out and high needle was set to 2 1/4 turns out
-I am able to get the engine started, but am unsure of some adjustments

My questions:
1) Is 125 psi sufficient compression?
2) Assuming compression is sufficient and given that crankcase holds vacuum and pressure, should I be concerned about the piston scoring?
3)Does anyone know the proper default settings of the low and high needles on the Ruixing H225-50 card for this Poulan?
4) Does anyone know the proper open throttle RPM for this Poulan (so I can properly adjust the high needle)?
5) What would cause this piston scoring? Piston rubbing on skirt? Would running on gas only (no oil) lead to this?

And if I'm not asking all the right questions, any other words of advice would be appreciated.

Thanks,

Tim

My questions:
1) Is 125 psi sufficient compression? Yes

2) Assuming compression is sufficient and given that crankcase holds vacuum and pressure, should I be concerned about the piston scoring? Yes, Piston and cylinder are toast, And cost prohibitive to repair and will prevent any attempts to make it run correctly.

3)Does anyone know the proper default settings of the low and high needles on the Ruixing H225-50 card for this Poulan? Not published, but generally set to make saw run smooth at idle and not stumble on accelerations

4) Does anyone know the proper open throttle RPM for this Poulan (so I can properly adjust the high needle)? Poulan claims 9000 rpm for max power. Generally set the high speed screw will cutting to get best performance.

5) What would cause this piston scoring? Piston rubbing on skirt? Would running on gas only (no oil) lead to this? Generally most times it is due to being run too lean, which could be caused by mechanical issues, or just set too lean due to EPA standards.

ILENGINE said:

My questions:
1) Is 125 psi sufficient compression? Yes

2) Assuming compression is sufficient and given that crankcase holds vacuum and pressure, should I be concerned about the piston scoring? Yes, Piston and cylinder are toast, And cost prohibitive to repair and will prevent any attempts to make it run correctly.

3)Does anyone know the proper default settings of the low and high needles on the Ruixing H225-50 card for this Poulan? Not published, but generally set to make saw run smooth at idle and not stumble on accelerations

4) Does anyone know the proper open throttle RPM for this Poulan (so I can properly adjust the high needle)? Poulan claims 9000 rpm for max power. Generally set the high speed screw will cutting to get best performance.

5) What would cause this piston scoring? Piston rubbing on skirt? Would running on gas only (no oil) lead to this? Generally most times it is due to being run too lean, which could be caused by mechanical issues, or just set too lean due to EPA standards.

Click to expand...

Or owner didn't add enough/any oil to the fuel