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Hi guys I have a Husqvarna 455 rancher it starts up within two pulls and idles great when you grab the throttle its boggy and won't rev up it doesn't die but won't rev every once in awhile if I feather it a lot I can get it to rev up but it's VERY finicky and every once in awhile it will back fire here's what I've done to the saw so far I've replaced the piston rings and cylinder I've put a brand new carb on it and a brand new ignition coil I put a brand new fuel line on it along with a fuel filter I have also taken the spark arrestor out with no luck I've tried every thing seems like the saw is sucking to much air it has a brand new oem carburetor on it I out new piston cylinder and ring on it because it didn't have compression after observing the ring the saw looked like it had been running Lean for awhile I can't figure this thing out I've replaced all crushal parts what could I be missing?

Did you check the bore for diameter & ovality ?
If so how ?

You need to do a leak down test above (combustion chamber ) and below ( primary compression ) the piston.

There are a pair of seals on the crankshaft.
If they are not in good condition the saw will suck air.

What makes you think it is running lean ?

The ignition module will either work, or not work.
Or if it wants to confuse you, work cold and not work hot.

An overly rich fuel mix and / or an overly retarded spark will allow the engine to start easy but will prevent the engine running fast

A lean carb or over advanced spark makes the saw a right royal PIA to start,

So judging purely from what you have said I would suspect the idle ( low speed ) jetting is correct and the high speed is lean.

need to rihen the high side of the carb if possible. so many of the new saws have fixed jet carbs.