Chainsaws

I would have thought it is a crack in the intake boot allowing it to lean out too far while the workload is stringent.  but after reading that these symptoms have been on-going since the saw was new,  then I doubt that is the issue.  now I lean toward bad crank seals.

hard to believe a mechanic would allow the saw to leave without fixing it.  if you have access to a vaccum gauge pull 10 or 11 lbs thru the impulse hose and sit on it.  if it holds this not the issue.  if you do not have a vaccum gauge,  reduce regulated air pressure down to 10psi at your blowgun hosel.  pull the recoil assembly and the flywheel.  pull the clutch.  lay the saw on its side, one side at a time, drizzle very soapy water onto each seal one at a time and fill 10lbs of air into the crank.  if the seal begins to blow snot bubbles this is the problem.  if we determine that this saw was shipped with damaged or badly installed seals, then Husqvarna owes you...  good luck brother...  I am Robert.  I repair/re-build saws professionally.

have you tested the vacuum and compression cold and hot?  I never heard any input on values.

what is happening?

if you take it back to the same shop, you might need to explain how to do a vacuum test.  any mechanic that allows a saw to go without repairing it, is at best, suspect.  you need 2 pieces of hard rubber cut to fit and seal over the intake and exhaust manifolds.  then you need a simple bracket fabricated to tighten the two rubber covers down airtight over the manifold openings.  after doing this you simply insert the hand pump vacuum gauge into the impulse hose.  make certain the hose is intact no holes, no cracks.pull the pump up to 10 or 11lbs.  if it holds the seals are okay.  same inspection with the intake boot, no cracks. also the muffler needs removed so you can torch the carbon out of the spark arrestor screen.

the compression test is very simple.  pull the spark plug-insert the correct size adapter into the plug seat and slowly pull the recoil starter until you reach max compression.  I want a cold value and a hot value.

it is very possible the air leak is between the magnesium casting and the crank riser.  the 350 is notorious for those 4 crank bolts vibrating loose.  to gain access to tighten these 4 bolts,(which must be done anyway),  you must remove the handlebar and then the fuel tank which is also the rear handle.  be gentle with everything as you disassemble all related components.  use Loctite on the 4 bolt threads and install them one at a time(remove them one at a time also) leaving the others until each is re-installed.  use an inch pound click type torque wrench once all 4 are reinstalled with Loctite use a cross pattern to 120"lbs of torque.  no more than 10lb/ft of torque.  this could very well be the cause or a part of the cause.  at any rate, this must be done to both of your 350's.

(you will find the crank bolts on the very bottom of the saw) under the body of the fuel tank.  the antivibe springs will need re-tightened and make certain of the rubber inserts that prevent bump are in properly.

I understand herb.  the necessity of that crank to hold vaccum is really imperative.  if it holds correctly, that is what allows the engine to draw in fuel while the saw is vertical, upside down, or turned over sideways on either side. otherwise gravity would not allow fuel to reach the combustion chamber.  I am almost certain the 4 bolts have come loose allowing vaccum loss. those bolts are hidden under the fuel tank on the bottom of the saw.  they draw torque between the jug and crank riser casting.  the seals are likely in-tact.  350's are infamous for those bolts coming loose...