Echo CS 400 chain saw wont run

[fishhh4]

Backing out the "L" screw gives it a richer mix at acceleration...

If you don't have a "pac man tool " To adjust it . I used a  Blue electic  connector .Turn to left a little . I will bet this is the problem .

[pprobus]

I have an older CS400 chain saw and it has been a dream.  This morning I got it out and it will start and idle, but when I pull the trigger, it dies.  I very recently changed the spark plug, air filter, fuel filter and has new gas. Any thoughts

Do not touch the carb settings!!!  I can't stress that enough.  The chainsaw ran fine the last time you used it, right?  That means the carb settings were fine.  99% of the issues I have found with small engines is that old gas has gummed up the carb and all that needs to be done is to tear down the carb for a good cleaning.  I know you said you have new gas in there.  But did you remove the old gas and then install new gas or did you run the saw dry after the last use?  If you dumped old gas and put in new, then its highly likely there was still old, gummed up gas in the carb and that you will need to clean it. But before you start pulling the carb from the saw, there are a couple of other things to check.

Another possibility is that the new filter was put on wrong so that the gas is trying to go in the wrong direction, is there an arrow on the filter housing?  Did you ensure you put the arrow in the right direction?  What you describe is a classic case of having the choke in  the wrong position.  Did you use the choke to start the engine?  Did you remember to open the choke after it started?  If you didn't use the choke to start, start the engine and close the choke and try to rev up the engine.  If the engine revs up with the choke on, wait until the engine warms up, shouldn't take anymore than 5 minutes and see if you still need to choke the carb to get the engine to rev up.  If you do, that means you need to clean the carb, which means pulling it from the saw and pulling it apart (note the setting of the carb adjustment screws by gently closing them and counting how many turns it takes to close them, try to pay attention to 1/4 - 1/8 turns to be as accurate as possible, although you likely still need to fine tune the settings, getting them close means you know the engine should start and run well enough to be able to do the finetuning rather than struggling to find settings to just get the engine to run) to clean in every nook and cranny.  You may pull it apart and find everything looks OK, I have run into this before as well, I use spray carb cleaner with those little straws and spray it into every hole, wipe every part, etc.  put the carb back together and have the engine run fine afterward, despite not seeing any obvious signs of gum or varnish in the carb.  I also had one instance where after cleaning the carb twice, I still could not get the engine to run correctly, cleaned it a third time ensuring I hit everything with carb cleaner and the third time was the charm in that case, but that was for a much larger engine (20 HP Briggs opposed twin). 

My 70cc Honda scooter taught me 20 years ago that if you have to adjust the carb settings, the carb needs cleaning. 

Good luck,
Paul

[Cian]

Do not touch the carb settings!!!  I can't stress that enough.  The chainsaw ran fine the last time you used it, right?  That means the carb settings were fine.  99% of the issues I have found with small engines is that old gas has gummed up the carb and all that needs to be done is to tear down the carb for a good cleaning...

Nodding to this.

[Roly]

Nodding to this.

3 rd here.  Unless someone messed with the adjustments it is crud of some sort if you get it running by adjusting the screws. The crud will move and you will have problems again.   Roly

[pprobus]

3 rd here.  Unless someone messed with the adjustments it is crud of some sort if you get it running by adjusting the screws. The crud will move and you will have problems again.   Roly

That may be true, but what I found was that adjusting the carb only delayed the need to clean it.  Here's my experience, with my 70 cc scooter, the engine would run fine all summer, summer #1, leave it with gas over the winter at my parent's vacation property, next summer, needed to adjust the carb to make it run OK, again, notice a deadspot, but works well most of the time.  Runs OK all summer, second winter, third summer comes and can't adjust the carb enough to get the engine to run right.  Can get to run acceptably but it has deadspots, hesitation, hard to start, etc.  Maybe that's caused by the moving around of the crud, I just assumed it was the buildup of crud.  Clean the carb, reset the settings, everything is good again.  Did that a couple of times before I read somewhere to run the carb dry and leave the carb dry over the winter.  Did not have another problem for the last couple of summers I rode that scooter by doing this.  I try to do this with my equipment.

Paul

[DaveHo]

Ethanol gas is hell on plastic fuel lines.  The root cause of every small engine issue I've encountered recently has been deteriorated fuel lines.

[Phil Thien]

Agree w/ Mr. Hooks, you can often find inexpensive new carbs on eBay.

New carbs do wonders.

And rebuild kids are often nearly as expensive as a new discounted carb.

And run it dry at the end of each season.

[doobes]

Before you do anything else, clean the spark arrester screen in the muffler.

The only time my Echo weed eater is a problem is when the screen is plugged up.

[wannabedivin]

up date.  Once it gets warm I can feather the throttle to get it to full speed and it will stay constant. 
We can still get real gas here so ethynol is not a problem
Once it is running, and i pull the choke out a little it will rev
Almost all have suggested the fuel vent may be clogged.  This is a rookie question but where is it.  It is not on the parts diagram from the owners manual.  The next lower model has it right on top once the cover is removed.  I pulled the cover and cannot see where it is or would be.  I searched you tube and google. Everyone has a part number but not sure where it is.  Once find it and check it, then the carb is next

[pprobus]

up date.  Once it gets warm I can feather the throttle to get it to full speed and it will stay constant. 
We can still get real gas here so ethynol is not a problem
Once it is running, and i pull the choke out a little it will rev
Almost all have suggested the fuel vent may be clogged.  This is a rookie question but where is it.  It is not on the parts diagram from the owners manual.  The next lower model has it right on top once the cover is removed.  I pulled the cover and cannot see where it is or would be.  I searched you tube and google. Everyone has a part number but not sure where it is.  Once find it and check it, then the carb is next

That's classic signs that the carb is dirty.  It happens with non-ethanol gas, too.  BTW, while I am not certain where the fuel vent would be, I think it is in the fuel tank cap.  I find it highly unlikely its dirty or the cause, but worth a shot to clean, if you can find it for certain.