550xp mk 1 help

[Husqvarna King]

Using the 550 at work today and was chasing a willow stem through and the saw just stopped dead, had been running fine all day. On inspection it has a good spark but no fuel is getting through to the cylinder.

The fuel pipes on top of the carb look ok but I can’t guarantee that then haven’t got a small split. In the fuel tank the pipe is all attached and the fuel filter pickup is at the bottom of the tank.

What should be the first thing I look at and or change? 
Many thanks in advance 

 

Edited January 16 by Husqvarna King
I’m a numpty

[spudulike]

Are you sure that the piston hasn't nipped up? Does the engine compression feel normal on the recoil handle? It is worth removing the muffler first and taking a look at the piston through the exhaust port.

 

Other than that, does the carb prime OK with the primer bulb? If you pull the saw over say, 20 times on full choke, is the plug still dry? If you turn the engine upside down with the plug out, if you pull the saw over (upside down) does fuel run out?

 

If the saw is still dry, you may have a serious air leak in the engine but it is still worth checking out the gauze strainer and pump diaphragm.

[Husqvarna King]

31 minutes ago, spudulike said:

Are you sure that the piston hasn't nipped up? Does the engine compression feel normal on the recoil handle? It is worth removing the muffler first and taking a look at the piston through the exhaust port.

 

Other than that, does the carb prime OK with the primer bulb? If you pull the saw over say, 20 times on full choke, is the plug still dry? If you turn the engine upside down with the plug out, if you pull the saw over (upside down) does fuel run out?

 

If the saw is still dry, you may have a serious air leak in the engine but it is still worth checking out the gauze strainer and pump diaphragm.

Thanks for the reply Spud 👍 the saw is put away for the night but I did think that maybe the compression is a little low but it’s normally so easy to pull over that I don’t take much notice. I tried pulling it over several times and then checking the plug and it was still dry but I could smell fuel. Haven’t tried pulling over upside down so will try that tomorrow and have a look at the piston.

thanks again 

[adw]

I agree with Spud, it sounds much like it has seized the ring in, so muffler off and check the condition of the piston through the open exhaust port, it could also have an issue further down, possible main bearing cage broken up which caused the piston seizure, my gut feeling is this machine will need stripping fully down.

[Husqvarna King]

Thanks, not what I wanted to hear 😬

[adw]

Keep us posted please.

[Husqvarna King]

Will do 👌

[Husqvarna King]

An update….

saw does seem low on compression, it won’t pick up from the starter cord.

when turned upside down fuel doesn’t run out of the plug hole but it is wet with fuel.

Took the muffler off and attached pictures of piston

[spudulike]

I don't like the look of all those streaks on the piston and if the decomp valve is OUT and the saw pretty much falls to earth when held by the starter then it is lacking a significant amount of compression.

The damage doesn't look like a heat seize so more likely, one of the main bearings has slowly failed....ouch.

Pull the cylinder off and take a closer look....if the compression is Way Down...as Elvis sang.

[Husqvarna King]

2 minutes ago, spudulike said:

I don't like the look of all those streaks on the piston and if the decomp valve is OUT and the saw pretty much falls to earth when held by the starter then it is lacking a significant amount of compression.

The damage doesn't look like a heat seize so more likely, one of the main bearings has slowly failed....ouch.

Pull the cylinder off and take a closer look....if the compression is Way Down...as Elvis sang.

Are you still doing work on saws Spud?