Echo cs 550

[randyize]

I just picked up an Echo cs 550 which the owner was selling after running it too lean and trashing the cylinder and piston. Can anyone explain to me what is going on with the intake side of this model? It has reed valves in the transfer covers connected up with a rotary valve intake situated on top of the carburetor. The transfers themselves seem to be very restrictive for a saw of this size. The previous owner had removed the limiters on the carburetor which no doubt led to burning up the top end. The saw has very few hours on it and I would like to get it back up and running.

 

[Piston Skirt]

I just picked up an Echo cs 550 which the owner was selling after running it too lean and trashing the cylinder and piston. Can anyone explain to me what is going on with the intake side of this model? It has reed valves in the transfer covers connected up with a rotary valve intake situated on top of the carburetor. The transfers themselves seem to be very restrictive for a saw of this size. The previous owner had removed the limiters on the carburetor which no doubt led to burning up the top end. The saw has very few hours on it and I would like to get it back up and running.

It had an alternative version of stratified scavenging.
Reed valves are there to delay the mixture entering the cylinder before it is ventilated by clean air.
In simple terms just as any strato engine it is there to avoid unburnt fuel to go straight into the muffler.

The rotary valve on top of the carburetor is to control clean air passage.

 

[Wood Doctor]

Removing the limiters on the carburetor was a disaster waiting to happen, assuming that removing them was necessary for it to run. Sounds like he got carried away and the engine paid the price at the top end speed. I only remove limiters as a last resort and only after the saw is several years old and not running right. Hard to believe this engine had very few hours on it.

Sounds like you need a top-end rebuild. Not impossible, but Echo parts are not cheap.