Echo 400 trouble

[nwmo_aggie]

Had the saw for a few years. Run nothing but 91 oct gas + echo oil in it.
Hadn’t used it for 60 days or so, and now it will idle but won’t rev up past about 1/2 throttle.
I’ve blowed a little air back through the fuel line, and seems ok that way.
It almost seems like it’s building pressure in the gas tank, like the tank vent tube is plugged, but I’ve also cleaned it, and when I attempted to run it on its side with the cap loose, didn’t make a remarkable difference. I’m sort of running out of ideas to chase, so open for input.

 

[jimrb]

How did the muffler look when you inspected it? Those spark arrestor screens get clogged up in many 2 cycle engines.

 

[nwmo_aggie]

How did the muffler look when you inspected it? Those spark arrestor screens get clogged up in many 2 cycle engines.

Probably oversight on my part. Hadn’t pulled muffler.
Will idle all day long, but acts like it starves out when you try to rev it up much past 1/2

 

[FlyingDutchman]

.Pull the muffler. Clean out the port... mod the muffler, punch out catalyst. Messy nasty time consuming job. The catalyst is very hard and the pieces of it are very sharp.

Pull the limiters off the carb. Retune.

 

[FlyingDutchman]

Also... If you have winter fuel in there, it will boil in the tank if its warm out now. Try different fuel.

 

[4CornersPuddle]

nwmo_aggie, have you sorted out your saws problem?
I just got a basket case CS400 up and running yesterday. It's a very low hour saw that a wood carver had given up on.
The throttle shaft screw that retains the butterfly had backed out and gone into the engine, cracking and gouging out the piston skirt. The screw was plastered to the inside of the crankcase; it was no more than a thin flat disc.
Fortunately the cylinder was not damaged, nor any other parts of the engine.
While I had the saw apart, I gutted the muffler. Flying Dutchman's description of removing the catalyst is entirely correct. I ended up with nasty slivers of metal imbedded in my fingers from using the Dremel to rout out the converter, and the baffle and outlet of the muffler.
I stole a throttle shaft and butterfly from the carb from a junked Shindaiwa 360, got a piston and brake band from eReplacement Parts, and put it all back together. That little saw, with Bailey's 3/8 LP full chisel chain, really cuts.
I do notice the throttle linkage doesn't quite open the butterfly all the way. There probably is about 10% of the throttle shaft's rotation that isn't happening. I'd guess this is not your revving problem, as you say beyond 1/2 throttle it seem like your saw is starving for fuel?
I'm impressed by the engineering of this saw, with the exception of all the crap stuffed into the crowded carburetor box. What a mishmash of wires, tubes, linkages.

 

[nwmo_aggie]

Yeah that area around the carb is pretty busy.
Simple things in my case. I did end up swapping in a new carb as I was sure that was it. At some point on a bit of a whim, I put on a new fuel filter and it runs fine now. I’m still quite perplexed by that. I’d inspected and blown out the filter, certainly no sawdust or junk visible, but sure enough.
Didn’t do the cat on this one.

I have another 400 that I actually bought off a guy here for parts. Has a visibly scored piston. He swore it wouldn’t run. I gutted the cat, twisted on the carb and been running it to build fence and cut brush with for probably 4-5 years. Just won’t die