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Auto tune is a very reliable system, however it can be its own worst enemy, auto tune will always try to keep the engine at full power, so if the air filter is part blocked it will lean the mixture to compensate, the orange frame air filter is 25 micro and even thought they look clean they can be blocked, and this in turn causes the carb to lean off, depending on the age of the saw there have been many updates, most to improve acceleration and hot restarting, idling is set via auto tune at 2750 rpm, the first thing you lose when there is any cylinder or piston wear is the idle, if these are mark 11 machines a pressure vac test must be done as they are quite prone to the crank seal behind the flywheel leaking. Hardened metering diaphragms have become an issue due to all the fuel issues we know very well, again depending on the age of the saws a firmware update would be a good idea, also to see the L circuit number, the numbers runs from 5 jet fully open to 150 jet fully closed, this figure can give an idea what may be going on, the fault codes given in cst are all based on these settings, base setting is around 70/80, as Steve said it is still a two stroke engine so can have all the usual two stroke issues, fuel system, engine condition etc.

No it could well be a leak which will get worse as the saw heats up, also if it’s an x torque machine check the induction boot is correctly aligned to the cylinder.

I would be a bit concerned that something has come from down below to cause that, maybe a bearing cage breaking up, before fitting a new cylinder I would at least pull the crank seals out to see the bearing cages.

Could be a few things from running too lean on the carb low circuit, to an air leak, to a blocked tank breather, to a part blocked fuel filter, if the saw has been left with fuel in it for a long length of time the metering diaphragm could have hardened.

Do not remember there being a Husqvarna 454rxt?

The bigger question is why are the shearing the key? as I see the only way it happens is if the flywheel has been removed and not sufficiently tightened when re fitted, or it has been miss aligned on the crankshaft and the nut tightened down.

I am well aware the taper holds the flywheel, however the chance of lining up the broken key in the keyway exactly is pretty slim, you will end up with the saw ripping your fingers out of there sockets.

Good luck with that!

I am pretty sure there is a difference in the flywheels between the 550xp mk1 and the 550xp mk 11, so be careful what you order.

The answer is no, plus if it’s a G then it has the generator magnets inside so needs to be a G flywheel if you want to continue with heated handles.

Bearings and seals will be no problem as they are still used on the K1270, pretty sure there will be an Oregon sprocket available for it or the 2100/2101/298, the crankcase gasket may be an issue but could always be made as was not very complicated.

Don’t how they got the brass neck!

It was basically a 2100 with a smaller cylinder and the 480fuel tank, mid 70s how long do you expect a manufacturer to carry spares for an old saw for? What sort of parts are you looking for?

Why is the a picture of a Husqvarna K970 on their labels , Husqvarna sell their own alkylate fuel, so why would they promote Aspen?

Machine running to rich, or far to much oil in the fuel, or poor quality two stroke oil in the fuel, an air would have made it run lean, how much and who’s two stroke oil are you using? only ever seen it once but if the crankcase gasket is leaking then chain oil can enter the crankcase.

Stale fuel can cause all sorts of issues, however in my humble opinion inadequate maintenance is a big cause of premature failures, poor chain sharpening, blocked fuel or air filters, allowing the starter cover grills to block ( this is basically a stationary engine, so all cooling air for the cylinder comes via the cover).

He won’t make it to 90 breathing that lot in.

Husqvarna XP oil mixed at 50.1, depends on how much you want to spend whether you go for mineral or bio chain oil.

Oh my god, you can actually see the cutters going blue, yet another chain ruined!

This is quite normal, the oil is sent through the unused bar adjuster hole and into the side cover, if you look in the side cover there is a rubber Chanel which then feeds the oil into the oil hole, I hear this all the time but when you look at it it’s quite simple.

I would like to say it never happens, however I have seen more than I should, when they go it tears the crank seal which obviously effects the running, a pressure test will quickly tell you the seal is leaking, most common seal to leak is the flywheel side, once the seal is removed you will see if the cage has gone, if not the just replace the seal, they are not easy to fit as you need to get them over the inner race of the bearing without knocking the spring out of the seal, on the slightly plus side the cylinder and piston usually come away with no damage, another tell tail is if there is signs of melted plastic in the spark arrestor.

Not to sure you will find a suitable bearing, also bear in mind the crank seals are pressed into the bearings, there is now yet another new material from another supplier for the bearing, there is no plan to to fit a steel cage bearing, the new supplier is also supplying the bearings for the 592xp with no issues.

The drive side seal is in the pump housing, so yes you need the seal sleeve tool, or a suitable way to smooth the way over the crank step.

What is this obsession with replacing carbs, it has to be the top spare part claimed for under warranty, this i also heard from Honda during some training, black smoke from the engine is running rich, so air filter as suggested, carb flooding.

Sorry I’m no climber, however all the mk1 and mk2 machines I see are on 10 and 12” bardo’s, do not see many on 14”.