Motor runs fine at first but when you go to full throttle the motor stalls and will only keep running at a lower idle? seems to be fuel related so I checked the fuel filter its cleen. I then found a fuel pressure gage and checked the fuel pressure in idle and full throttle. after priming before starting 10-12psi. in idle 4-5psi. in full thottle drops to less than 2psi. I do not know what is the correct psi. per condition? how should I proceed?

Brad:

Go back to the carburetor adjustment screws and snug them down gently. Do not use force on those screws or you'll damage the needle valve seats. Turn both screws out one and a quarter turns out and start the saw. The motor should stay running.... if not adjust the screws until it stays running. Turn one screw in until you hear the motor start to stall, then turn that screw out just a little bit. turn the other screw in until the saw starts to stall, then turn that screw out a little bit. Now if the saw bogs at full throttle, turn one screw out one quarter turn. See if the saw runs at full throttle... if not turn that same screw in to where it was and try the other screw the same way. If you're good, you can adjust the screw while the saw is running to get the best full throttle run. This is not an exact science, and it takes time and many adjustments to get the saw to idle and run at full throttle. Good luck... and have patience.

it could be the idle air valve or idle control valve

Clogged idle circuits in your carbs. Clean jets and passages.
You can try suck dirt out, therefore: Screw the idle mixture screw out ( almost totally ), give full throttle ( 1 second ) and then hold your hand against the carb air intake.
This will give maximum suction and can suck the dirt trough tje circuits.
Also, first drain the carb(s) to be shure there is no water in it...

If your vehicle has one, and I think it does, check your EGR system. If the egr valve is full of carbon, it can be partially open, creating a vacuum leak. If the egr valve solenoid is bad, it could be opening the valve at the wrong time, also creating a vacuum leak. Unplug the egr vacuum hose, plug the open end of the hose and start it and see what it does. A picture of the egr is below.

o2 censor may be dirty or need replaced

yes it could be a fuel related problem, when was your last tune up, it could also be a spark issue, old or corroted spark plugs will sometimes not put out the correct amount of heat to ignite the gas correctly till it runs for a while, if the check engine light isnt lit, it will almost have to be something simular to this

Sound like the fuel pump is not keeping up with the engine's demand. Check it out. Good luck. Hope this helps.

o2 sensors

check your transmission fluid,the motor will stall when fluid is low

Have you had the throttle valve cleaned?

Here is the most common cause of surges and stalls, it is the idle speed control air-bypass valve and throttle valve, they get full of gunk over the miles and cause idle issues (stalls) like yours, Get a can of intake cleaner from any local parts store, not carb spray, intake cleaner, it is made by a company called CRC, remove the air intake hose to the engine, hold the idle high so the engine won't stall, then spray the can of cleaner into the intake while keeping the engine running, use at least 1/2 the can, shut down the engine and disconnect the battery for 5 minutes, then restart and complete a number of mixed driving cycles, town, freeway, stop and go etc., after a few days the problem will go away as the system will relearn to the clean intake.