Small Engines (Lawn Mowers, etc.): Poulan 295 Chainsaw Cannot Adjust Carb, poulan pro 295, felling trees

Question
My Poulan Pro 295, 20", chainsaw is about 7 years old. It has been a real workhorse, felling trees as big as 24" and producing countless loads of firewood and slash.

Last year, it would not idle some of the time. Then it got so it would not idle at all, and then would not cut with full power. I first suspected that it may be low on compression, considering its age and work load, so I checked that first. Compression is 110 pounds.

I had already replaced the fuel filter and fuel lines because the filter had clogged. Those have less than 10 hours run time on them.

So I decided to rebuild the carburetor. It's a Walbro WT610. I started with the D20-WAT kit. I blew out all the passages with carb cleaner and compressed air. After the rebuild, it would start, but not continue running. I started with the mixture screws turned out 1-1/4 turns as the Poulan manual says. It would start and stall. I gradually opened up the needles together. At about 4 turns each, it would start and run on fast idle, would almost run at speed, and would not idle.

That's way, way too far open on the screws. It seems like it's fuel-starved.

I got a K20-WAT kit for it, and replaced the screens that time. The result was the same. My dad works on some small engines, and he decided to file the center post of the diaphragm, just to see what affect that might have. "Can't be any worse than it is now." That did no good.

So I got another K20-WAT kit, and this time I replaced not only the screens, but the welch plugs, so I could be absolutely certain everything was clean and open. I also made sure the needle lever was set to the specified 0.067" setting.

I double-, triple-, quadruple-checked the assembly order of the diaphragms and gaskets: Body > gasket > diaphragm > cover. Body > pump > gasket > surge diaphragm > cover. The first two rebuilds I did not include the surge diaphragm in the pump, because it was not present originally. The third rebuild, I included the surge diaphragm because it was clearly shown in the part list and diagram.

Still the same result. If I turn the screws out 4 or 5 turns, it will almost run, and will not idle.

I have also replaced the gasket under the carb, twice. Air filter is clean. Everything by the book as far as I can determine. Ignition is hot and spark plug is a new fine wire electrode model that cross-references to the OEM number.

Finally, I suspected the fuel cap. It never did suck in air, and sometimes would spit out some fuel, when it was removed. That seemed correct to me. But today I pulled the fuel cap off and inspected it. It has no visible vent. Outside the cap, in the center, is a slot that looks like it could possibly be a vent. But inside it is all smooth plastic. I even pulled the plastic retainer cord out of the center, thinking the vent hole might be in the socket above the cord's ball. No. It's all smooth plastic inside. As far as I can determine, this gas cap does not have a vent.

Is there a vent somewhere else on the fuel tank?

Do you have any other ideas? I've got lots of brush and trees that need cut, and no working saw. I really don't want to chuck this one and get a new one (but I'm tempted). I can't find anything wrong with it. But it won't run.

It just occurred to me that I have not checked to see that the flywheel is correctly positioned. I have no reason to believe it's not, as it has never been removed. But maybe the timing has moved?

Thanks for any and all input.

Answer
Did you inspect the carb metering lever arm? You can download the Wal-bro manual to verify the height but most meter lever arms are set flush with the bottom of the carb housing.

Spark arrestor screen?  Is it clogged?  Remove the muffler and clean the muffler ports and cylinder port.  Test with the muffler off the engine.

Read valve or any other intake gaskets...are they leaking?  Did you perform a crankcase pressure test to see if any other gaskets or seals are leaking.  A leaking seal or gasket can cause your problem.

As for the tank vent most of the Poulans vent through the fuel cap threads.  If you think the engine is not pumping fuel due to vacuum in the tank just try running the engine with the cap off...engine on it's side.

I suspect carb/fuel issue but the compression could be border line but it should run on full speed if you can start the engine.

Let me know about the metering arm height and spark arrestor.

Eric