Low Compression in Echo SRM-225 Weedeater

[nick890]

I have 2 Echo SRM-225 weed eater. I was having issues starting them, so I first checked for compression. One would give me about 80psi and the other was about 70. I disassembled and opened the cylinder to find what I would consider to be minimal normal wear. I checked that the ring was free to move, and I cleaned the inside of the cylinder and the piston itself. It had little to no effect. I decided a factory Echo piston and ring may help enough to get some more life out of the weed eater, so I bought one for about 45 dollars and put it in. My compression actually dropped to 55psi. I am not sure how it could become less with a brand-new piston and ring. I attempted to install the new piston in the other weed eater, and it also would only achieve 55psi. I really can't understand how the compression is so low. Is there anything else that can affect compression? I have photos of the original piston and the cylinder to show that these are not scored up and to me look to be in overall good condition.

 

[Steve]

Compression is lower with a new piston and ring because the ring has not fully seated to the not perfect circle of the cylinder walls. Once the engine is running the ring will begin to wear to the irregular cylinder and "break in" to make a complete seal, and restoring compression.

Have you checked to make sure you have spark?

Have you put some fuel mix down the throat of the carb?

80psi cranking will be enough for the engine to start and run. What kind of compression gauge are you using? Some compression gauges are not accurate on a such small displacement engine.

 

[nick890]

Steve
Thank you for the quick response. I did not even think to try to run this with the new piston. I just checked compression, and it was low, so I assumed I would never get it to start. I went out and checked for spark. The spark is good. I then used starter fluid to get it running, and it did start up. I replaced the carb before the piston, so I will have to tune the carb some since it is cutting out at full throttle. I tried to run for a couple of minutes without going full throttle. After 2-3 minutes of run, it cut off and a small amount of smoke was seen from the cylinder. I don't have a ton of time to work with it this morning. I will try to get to it this evening to see if I can get it running again and continue breaking it in. Thank you again. I will post when I get further along.

 

[Steve]

Your carb is too lean. You will need to open the high screw to add more fuel.