So it idles fine? Sounds to me like the carb is out of adjustment, most likely just the high speed jet. There is a good chance it is too lean. Try turning the "H" screw out 1/2 turn and see if it is any better. If there are plastic caps limiting this, you can take off the side of the saw, then pull the plastic caps off with pliers.

I did this to my dad's Poulan Wild Thing and adjusted it out. It went from a weak saw that wouldn't idle and started real hard to a decent weekend cutter.

There is a possibility that the low speed jet is improperly set as well, but since it idles fine I'd leave that alone for now.

I should have said something else as well. Make sure your spark plug is good and your air filter is clean before starting to adjust the carb. Not only could one of those things be your problem, but also it would make it so you adjusted your carb incorrectly.

And, I know it sounds silly, but your chain brake is off right?

If you didn't mess with your mixture screws when you rebuilt the carb, then don't touch them now. I would change your fuel filter and inpect your fuel lines for cracks and replace the spark plug. Sound like its not getting enough fuel.

I hadn't messed with my dad's 2375 and after a few hours of use it wouldn't idle at all. Turns out it was too lean from the factory and after the saw was worn in it wouldn't run right so I had to adjust the carb. Now it runs like a top.

If his saw ran for a year and half, I'm lead to believe the fuel mixture is not the problem. Sometimes messing around with the fuel mixture screws only mask the real problem. I've had this problem with my chainsaw as well. At first I cleaned the carb and adjusted the mixture screws. The saw ran ok for a while, but I could never get it to run just right. After a few months of on again off again useage, it wouldn't start. I found that the fuel lines were cracked sucking in air. Once I replaced them, it was now running rich. I reset the mixture screws back to stock and it runs great.

My dad's saw "ran well for 7 years" but he had only used it twice. I agree he should check some other stuff before messing with carb settings though, it's easy enough and could save a lot of hassle for someone that may not know how to tune a carb. Plus, like you said, just tuning it without checking other things might mask the real problem.

When a 2 cycle engine won't run above an idle the first check should be the muffler screen.

I'd check the air filter first but you should check both air filter and muffler screen.

I have found that most of the trouble with small two stroke engines can be attributed to either their carbs or their exhaust ports. Yes, there can be ignition problems but most of the time a magneto either works or it doesnt. Chances of it being the carb if it ran good yesterday but wont run today are slim. When a good running engine slows down, wont accelerate and becomes hard to start the first place I look is on the exhaust side of things. Remove the muffler and using a flashlight look into the exhaust port of the engine. If the exhaust ports are partially plugged then you have found your problem. Here is how to fix it. Using the pull starter or if you have the side cover off, turn the flywheel with your fingertips while looking through the exhaust port at the piston. Using the flashlight watch the piston move up and down in its stroke. Position the piston at the very bottom of its stroke to remove the carbon. Using a stick or a dowl rod or even a plastic knife, scrape the carbon out of the port. You do not want to be poking around in there with a screwdriver or anything metal because you do not want to gouge the piston or the cylinder. After your finished removing the carbon take the spark plug out and blow the dust out with either your breath or some compressed air. Point the exhaust port toward the ground and tap against the side of the cylinder which allows the remainder of the dust to fall out. Finish the job by cleaning the carbon out of the spark arrester screen either inside the muffler ar attached to its outlet with a screw.

While you have the case apart go over the bolts to make sure they are all tight. Pay particular attention to the crankcase and carb adapter mounts. On some designs you have to loosen the carb mounting bolts to get to the mounting block bolts behind the carb. If your unfamiliar try to find a schematic of the engine to guide you as to where the bolts are located. Generally these diagrams are available on the manufacturer's websites under parts.

Next, reverse flush your fuel filter with some Jet Spray and squeeze all of the fuel lines between your finger tips to make sure they havent rotted from the MTBE in the fuel. The fuel lines often get pin holes that will open up as you roll the lines between your index finger and thumb.

This is a basic 50 hour service on a two stroke engine. Reassembly is the reverse of how you took it apart.

Good luck and let us know if you have any questions.
Bob.

P.S. Remember these are small two stroke engines often being pushed upward of 12,000 rpm at high speed. Thats something like 200 power strokes a second. A little extra oil in the fuel will help keep your engine running for many years.