What's the next thing I should look for?

[Dwstwrt]

Are you using fresh fuel? I tried my chainsaw this past fall, fuel & spark—no go. I then took some from tank and lit it with a torch, it was like a candle burning—real slow. New mix and a couple of pulls, good to go!

 

[Graeden]

Is the safety switch connected? Do you have the On/Stop switch switched to on?

Link to owners manual: https://www.manualslib.com/manual/132533/Poulan-Pro-115153026.html#manual

 

[OzPete]

I'm at my wit's end. You all led me in the right direction when we found a scored piston. I changed it and the cylinder. Sealed it back up with Loctite 515 and with a coat of oil on the cylinder wall. Compression checked at about 125-130psi. There's a good blue spark and the spark plug is wet.

Won't fire.

The air filter is new. I checked the spark arrester and it was clean, tried to start with the spark arrester off.

Still won't fire.

I checked that the alignment pin on the flywheel is intact and the flywheel is seated on it correctly.

What can I check next other than the direction to a dumpster? Surely I'm close to getting this POS running

Sounds like its got a crankcase air leak .. which causes a dangerously lean air/fuel mixture .. which is probably what caused your original piston damage (partial seizure). Your scored piston wasn't the cause ... it was the result.
In a two-stroke engine, crankcase integrity (its air-tightness), is critical .. even more critical to the operation of the 'Two-stroke Cycle" than compression in the combustion chamber.
So my guess is a popped (or just worn & leaking), crankshaft seal behind the flywheel or behind the oiler pump on the clutch side.
F.Y.I. - It's considered pointless and particularly poor practice for a small engine mechanic to re-install a cylinder on a 2-stroke engine without performing a crankcase pressure test. In my shop my technicians know that at the outset, after removing the muffler and identifying a scored piston, I insist that they complete the diagnostic process by performing a Crankcase Pressure & Vacuum Test. Pic attached & Search it on Youtube.

 

[virtual_guy]

Sounds like its got a crankcase air leak .. which causes a dangerously lean air/fuel mixture .. which is probably what caused your original piston damage (partial seizure). Your scored piston wasn't the cause ... it was the result.
In a two-stroke engine, crankcase integrity (its air-tightness), is critical .. even more critical to the operation of the 'Two-stroke Cycle" than compression in the combustion chamber.
So my guess is a popped (or just worn & leaking), crankshaft seal behind the flywheel or behind the oiler pump on the clutch side.
F.Y.I. - It's considered pointless and particularly poor practice for a small engine mechanic to re-install a cylinder on a 2-stroke engine without performing a crankcase pressure test. In my shop my technicians know that at the outset, after removing the muffler and identifying a scored piston, I insist that they complete the diagnostic process by performing a Crankcase Pressure & Vacuum Test. Pic attached & Search it on Youtube.

It's been a bit since I checked in here but thank you. Having done some research here and on other sites I had already about reached that conclusion. I'll tear it down again when I get time and see what I can find.

 

[virtual_guy]

So if one or both crank seals is bad, would it not fire at all, even with some starter fluid? Seems like it should still fire with starter fluid put directly into the spark plug opening.

Also, I thought the plastic cylinder inserts were identical but I just figured out they have different part numbers. If I swapped the left and right inserts would it cause this?

 

[Rivets]

If you just swapped the seals, I would start by getting the proper seals for both sides an install them. This should be done anytime you open a two-cycle crankcase.

 

[Born2Mow]

So if one or both crank seals is bad, would it not fire at all, even with some starter fluid?

Without primary compression in the crankcase, the fluid never makes it to the combustion chamber.

That's what the man is telling you.

 

[Hammermechanicman]

See post #6
If you have decent SECONDARY (cylinder) compression and spark at proper time if you put a small amout of starting fluid in the spark plug hole. Not carb cleaner or gasoline. It will fire with or without PRIMARY (crankcase) compression. If it won't fire you either have a compression or spark issue. Ignition should be able to jump a 1/4" gap with blue spark. If it does the ignition will run the engine. If it does fire with starting fluid in the cylinder you can move on to possible primary compression issues.

 

[virtual_guy]

See post #6
If you have decent SECONDARY (cylinder) compression and spark at proper time if you put a small amout of starting fluid in the spark plug hole. Not carb cleaner or gasoline. It will fire with or without PRIMARY (crankcase) compression. If it won't fire you either have a compression or spark issue. Ignition should be able to jump a 1/4" gap with blue spark. If it does the ignition will run the engine. If it does fire with starting fluid in the cylinder you can move on to possible primary compression issues.

Thank you. I was sure this was the case and it points to a different issue. I have measured the cylinder compression and it's fine. I put starter fluid into the spark plug hole and it still doesn't fire. I can see spark but it is apparently insufficient. I'll look into that side of it.

Regarding crank case seals, I don't currently have a way to do a pressure test but I'm looking into that.

Thanks everyone.

 

[virtual_guy]

Ok I'm now on to something. In the process of this rebuild I had replaced the flywheel. The new flywheel came in a package that had the right part number on the outside but I failed to notice that it had the wrong part inside. The timing is a full 60 deg off when compared to the old flywheel. While I was a little negligent in not noticing the difference, at least now I have something that explains what I'm seeing.

A new, and hopefully correct, flywheel is on order.