Daniel Duffy
New Member
Hi all.
I'm so glad I've found this forum. Been fighting a problem with my saw for months and have been too stubborn to pay a shop to fix it when I know the answer's out there and I enjoy hands-on work. Here's the situation.
Have an Echo CS-400 saw that I've used only a couple of hours a year for last 6 years or so. Never had a problem. Then when I fired it up recently, it would only stay running on full throttle - it would not idle. Researched and it seemed a carb rebuild was in order.
Disassembled carb and installed rebuild kit. Carb was pretty clean to start. None of the gaskets were brittle, and the screens were not clogged but went ahead and replaced all anyway. Aired out all lines/chambers and followed up with carb cleaner but nothing was clogged to begin with - but wanted to be sure. Carb was now spotless and air/fuel would pass through every chamber freely.
Made sure all fuel lines were good and not cracked/soft, and fuel filter was clean. When I'd depress the prime bulb, fuel would flow freely up from the tank, and through the carb, so didn't appear I needed to replace fuel filter. Additionally, because it would run fine on full throttle (but ONLY full throttle), that also seemed to indicate fuel was flowing fine.
Made sure the air filter was clean. Checked spark plug for good spark with spark line tester, and checked spark plug gap. Checked compression, which also seemed fine.
Put it back together and followed Echo instructions for setting carb high/low and idle.
Now it starts up and idles better, but as soon as I apply throttle, it dies. I have however noticed that once it's warmed up, if I slowly apply the throttle, it CAN increase up to full throttle in a controlled manner. But if I want to just brap the throttle, the way you'd normally use a chainsaw, applying throttle as needed, it dies.
So did some more research, tore it apart again, triple checked carb was clean. Removed and cleaned spark arrestor, which didn't have much carbon build up anyway.
*Thought* I'd read that using straight, unmixed fuel might help. Tried that and the damned thing started up but wouldn't shut off - even when I turned the ignition switch to OFF. Had to dump the fuel to get it to finally die. Don't think it did too much damage - only ran like this for <30 seconds but it was crazy it didn't stop. No idea what that was about but it didn't fix the problem anyway. I was also mistaken - I needed to get pure fuel without the ethanol in it.
Replaced with regular 50:1 mix, cleaned out the tank, lines and carb (again), and it started fine - but again, would only idle. But again, once I applied throttle in a normal manner, it dies. It will only accelerate if I very slowly increase throttle.
Took it to a saw shop and they said they'd probably just replace the carb. But I don't want to pay someone to do what I can do myself, or pay to replace a carb that doesn't need replacement. And after having rebuilt the carb, I don't think it's the problem. I'd really like to figure this one out and have the satisfaction of fixing it myself.
Read through this thread but couldn't find anything new I don't think I've already tried:
https://www.arboristsite.com/community/threads/chainsaw-dies-under-load-or-full-throttle.229941/
The only thing I don't think I've checked is the impulse line. If I understand it correctly, it basically provides pressure to the carb to pump the fuel through, regardless of position of saw. Any time I've been testing, the saw has been level. Still, this seems to be the only part of the equation I've not checked. But if fuel flows enough to idle then could this even be a consideration? Could it be that it's partially clogged and under full throttle not providing *enough* impulse to pump enough fuel into the carb fast enough?
Any ideas out there for this? Have I missed something?
Thank you in advance for any ideas.
I'm so glad I've found this forum. Been fighting a problem with my saw for months and have been too stubborn to pay a shop to fix it when I know the answer's out there and I enjoy hands-on work. Here's the situation.
Have an Echo CS-400 saw that I've used only a couple of hours a year for last 6 years or so. Never had a problem. Then when I fired it up recently, it would only stay running on full throttle - it would not idle. Researched and it seemed a carb rebuild was in order.
Disassembled carb and installed rebuild kit. Carb was pretty clean to start. None of the gaskets were brittle, and the screens were not clogged but went ahead and replaced all anyway. Aired out all lines/chambers and followed up with carb cleaner but nothing was clogged to begin with - but wanted to be sure. Carb was now spotless and air/fuel would pass through every chamber freely.
Made sure all fuel lines were good and not cracked/soft, and fuel filter was clean. When I'd depress the prime bulb, fuel would flow freely up from the tank, and through the carb, so didn't appear I needed to replace fuel filter. Additionally, because it would run fine on full throttle (but ONLY full throttle), that also seemed to indicate fuel was flowing fine.
Made sure the air filter was clean. Checked spark plug for good spark with spark line tester, and checked spark plug gap. Checked compression, which also seemed fine.
Put it back together and followed Echo instructions for setting carb high/low and idle.
Now it starts up and idles better, but as soon as I apply throttle, it dies. I have however noticed that once it's warmed up, if I slowly apply the throttle, it CAN increase up to full throttle in a controlled manner. But if I want to just brap the throttle, the way you'd normally use a chainsaw, applying throttle as needed, it dies.
So did some more research, tore it apart again, triple checked carb was clean. Removed and cleaned spark arrestor, which didn't have much carbon build up anyway.
*Thought* I'd read that using straight, unmixed fuel might help. Tried that and the damned thing started up but wouldn't shut off - even when I turned the ignition switch to OFF. Had to dump the fuel to get it to finally die. Don't think it did too much damage - only ran like this for <30 seconds but it was crazy it didn't stop. No idea what that was about but it didn't fix the problem anyway. I was also mistaken - I needed to get pure fuel without the ethanol in it.
Replaced with regular 50:1 mix, cleaned out the tank, lines and carb (again), and it started fine - but again, would only idle. But again, once I applied throttle in a normal manner, it dies. It will only accelerate if I very slowly increase throttle.
Took it to a saw shop and they said they'd probably just replace the carb. But I don't want to pay someone to do what I can do myself, or pay to replace a carb that doesn't need replacement. And after having rebuilt the carb, I don't think it's the problem. I'd really like to figure this one out and have the satisfaction of fixing it myself.
Read through this thread but couldn't find anything new I don't think I've already tried:
https://www.arboristsite.com/community/threads/chainsaw-dies-under-load-or-full-throttle.229941/
The only thing I don't think I've checked is the impulse line. If I understand it correctly, it basically provides pressure to the carb to pump the fuel through, regardless of position of saw. Any time I've been testing, the saw has been level. Still, this seems to be the only part of the equation I've not checked. But if fuel flows enough to idle then could this even be a consideration? Could it be that it's partially clogged and under full throttle not providing *enough* impulse to pump enough fuel into the carb fast enough?
Any ideas out there for this? Have I missed something?
Thank you in advance for any ideas.
