Two stroke engine RUNS but QUITS – Today on Repairs101 – my neighbour brought me this old ECHO 150 hedge trimmer. To see if I could troubleshoot why it starts and idles but quits when you try to do any work.
This episode of Repairs101 is sponsored by PRINCESS AUTO. That’s where I got these Tri-Dollies. Great for moving furniture around easily. But I plan to use mine as camera dollies.
The Backstory
So he’s had this trimmer and another similar unit forever without any issues. But he and his son were out facing back this monster Cedar hedge and the machines quit. One after the other. Never to work again. They start; they idle. They even rev up. But they quit as soon as you try to work them. Now I didn’t need to hear any more. I was sure I had his diagnosis already.
Now a lot of guys will go straight after the carburetor and say “Oh it just needs some kind of adjustment, so…” But, you know it’s been my experience that once a carb is set up properly it rarely needs adjusting.
Check the easy stuff first
So your time is better spent checking the air filter… checking the exhaust isn’t blocked… check the spark plug and the spark plug wire and boot. Check the fuel filter… check the fuel tank breather… check the magneto… and really look around for anything that’s obvious. And then finally you gotta ask yourself: what manner of fuel was used? Because, you know, I hate to break it to you but…
This power pack came out of my STIHL 024 chainsaw when I loaned it to a guy I was working for and it came back NFG.
You can see here in the exhaust port that the piston skirt closes off the port for compression and ignition. Now looking in the intake port which is positioned lower: the piston goes right past the port and allows for the crankshaft and the connecting rod to be lubricated by the fog of air, fuel and oil.
Inside you can see there are these passages connecting the crankcase below the piston to the combustion chamber above the piston, to allow fuel vapour to cool and lubricate all the surfaces.
Permanent damage
Without the oil mixed in with the fuel heat will build up quickly and the cylinder wall and the piston skirt will erode on the exhaust side creating a gap where compression gas is lost when resistance is applied.
You can easily see how worn down this exhaust side is compared to the insignificant scuff mark there is on the intake side.
You can also measure inside the cylinder for “out of round” using telescoping gauges. Which is a lot trickier than I make it look here. And realistically there’s no reason to do this other than curiosity. You’re going to have to replace the power pack.
