Echo CS 3400

[raymcbride]

Hello everyone! I have picked up a echo CS 3400 at a swap meet. I clean the carburetor and replaced the primer bulb and all fuel lines and filters. It would start and run screaming with the choke on but when I would pull it off it would die. After messing up the fuel adjustment screws I bought another carburetor online and put it on and it does the same thing. I managed to get it running for a short while but it will not keep running. To me this seems like it might be an air leak but I'm not sure where it would be. Also does anyone know anything about a check valve on this model. Could that be the problem? I looked it up on a diagram online but I actually cannot find where it is exactly at. Any help would be muchly appreciated. Thanks.

 

[Bob Hedgecutter]

Top handle or rear handle variant?
First thing to do is remove the muffler and look through the exhaust port to see if the piston is all scored up.

Very likely a massive air leak from a loose engine pan of the clamshell or failed crank main oil seal/seals.

If the piston is well scored- you may be flogging a dead horse- not the easiest saw to work on and pull apart, aftermarket parts are not as easy to find for a cheap fix and they easily become an uneconomic repair.

 

[raymcbride]

Thanks, Bob! I will definitely check the piston. I recently tore into a weedeater where that was the case. I might add that it is holding 75-80 lbs of compression. Will post findings in a few days.

 

[Bob Hedgecutter]

Compression readings only count if they are taken with a tester specifically designed for small engines.
No way in heck it will run on 75-80 IF that is the true reading. Absolute minimum of 90 psi required to "run" but most require a minimum around 120-125 psi- especially small capacity 2 stroke engines.

 

[raymcbride]

Okay! I think I can still send back the compressor kit I bought and look for one for small engines. Thanks again bob!

 

[Bob Hedgecutter]

Okay! I think I can still send back the compressor kit I bought and look for one for small engines. Thanks again bob!

About the only ones that work really well and read true for small engines is the snap-on one and you know how much they cost.
Not economic for a one off repair.
First you need to get into it enough to see the piston, if it is all scored up- may not be worth the hassle- if it is not, then things can be saved.
Ideally a pressure and vacuum test will show if there is a leak of air- but this requires the intake and exhaust to be sealed off air tight and a means of introducing air under small pressure into the cylinder- not overly complicated, but does require some basic tooling, some rubber sheet ( line inner tube pieces) and if testing lots a Mityvac 8500- if not a tube and your lungs.

 

[raymcbride]

I checked the piston thru the exhaust and it looked really good. I will keep working on it see if I can figure it out. Thanks!