dolmar 111 - ticks over, won't rev up.

[Jonesyboy]

So, I rebuilt this saw about 18months ago, new gaskets all around, new flywheel, carb diaphragms and gaskets, new piston ring, cylinders mint inside, new crank seals, great spark, chain sharpened, rakers filed correctly.

Its been great since then, right up until a few weeks ago when it stopped in a cut and became hard to start.
Checked everything I could think of , checked IPL to see if I'd left something out, nothing evident.
Crankcase pressure test ok, crankcase vacuum test ok, carb needle valve holding pressure, fuel line holding pressure and vacuum, tank vents well under vacuum, cant really build up much pressure or vacuum there though.
Symptoms are:
Wont start unless choke is used, even when warm. Starts every time with choke though.
Idles but cant really increase or decrease idle speed using L screw, only the T screw.
Bogs out instantly upon giving the trigger a blast, or else wont rev up at all. H needle has no apparent influence on it, ie can't get it to run obviously lean or rich.
Engine sounds blubbery on idle, like its rich, but seems like its starving when I pull the trigger.

All I can think of now is impulse line problem somewhere or undetectable air leak somewhere or maybe vent priblem. Just about to write it off as deceased
, so any ideas on where to look before I launch it into the deep dark corners of the shed, never to be seen again?
Many thanks.

 

[Memo909]

Could be a tiny air leak around the carb or crankcase that is messing with fuel delivery because sometimes even a small gasket or O ring issue causes exactly that. Then check the impulse line for cracks or blockages; they're easy to miss but can cause bogging like the one you describe

 

[Jonesyboy]

thanks for the reply!
Replaced the carb gaskets with new cos they looked a bit ratty, cleaned out the impulse drilling as well. Placed a drop of viscous oil over the impulse drilling, pulled the saw over, it sucked the oil in and spat it out ,so the impulse seems fine.
Really at a loss as go what is causing this, I've had the saw 15+ years and this is the only time its let me down. Could it be bin time for the old boy?

 

[blades]

did you replace the filter on the end of the fuel line in the tank. seen those get gummed up . Carb diaphragms get old and stiff or sometimes develop a pin prick hole. just had a lawn tractor here that developed a blockage in the fuel line between the filter and the tank, looked like a bunch of snot when i blew the line with compressed air back into the tank.

 

[Jonesyboy]

fitted new fuel filter, new air filter, new plug, checked fuel line was clear, checked fuel line for sp!its, pressure and vacuum tested fuel line as well. Carb just had a new rebuild kit fitted, thinking tnere may be an issue with the needle or metering lever, as in the wrong type fitted? Am I barking up the wrong tree here?