Echo CS400 Troubles

[redunshee]

Rebuilding a cs400. New piston and carb rebuild ( USC and new kit). Issue is , the saw will idle but immediately dies when the throttle is squeezed,. I'm using the recommended carb settings(1 3/8 Lo and 2 1/4 HI). I've even varied the settings but still does the same thing. I believe its a carb issue but an wondering if it could be anything else? It passed a pressure/vacuum test and initial comp is 140. I've ordered an aftermarket carb but wonder if I should be entertaining other options.

 

[mountainlake]

Try 4 turns out on both then back in until it runs good. most of mine end up around 3 turns out Steve

 

[J D]

Did you blow the carb out with compressed air when you cleaned it? The main nozzle check valves don't tend to like that too much

 

[redunshee]

Try 4 turns out on both then back in until it runs good. most of mine end up around 3 turns out Steve

I’ll give it. Ry. Couldn’t hurt at this point. Thanks

 

[redunshee]

Did you blow the carb out with compressed air when you cleaned it? The main nozzle check valves don't tend to like that too much

No. Knew better than to do that.

 

[redunshee]

Try 4 turns out on both then back in until it runs good. most of mine end up around 3 turns out Steve

Well, it worked. Though there is still a bit of hesitation if I quickly squeeze the throttle. 3 open on The Lo and about 3 on Hi. Just 4 strokes slightly. Will attach bar and chain and see if I clean up the hesitation. I never would have guessed at the settings if u hadn’t commented. Thanks.

 

[J D]

Tuning should be done with bar & chain attached & the chain slightly looser than you would typically run it (so it only just pulls up to the bar). If you've had a spin on clutch off it's a particularly bad idea to run the saw without the bar, chain, & cover on as the clutch can come loose resulting in parts flying of at great speed.
For the Lo speed, you want to set it where the saw idles highest (adjust slowly as it takes the mixture a second to catch up), then richen it up a bit (screw out) so it drops about 500RPM... Usually 1/8 to 1/4 turn but might be more in your case. You should find as you richen it up (& adjust the "T" to keep idle speed up) throttle response gets better & better.
Then set H, then go back & check L, then re-check H (they don't effect each other much, but if one is way off it will have some impact on the other)

 

[jltrent]

Keep tinkering with the carb.

 

[redunshee]

Got saw running real well but can’t remove the slight hesitation when quickly squeezing the throttle. Squeeze it at a moderate speed and it’s fine or after it hesitates future quick blips of the throttle don’t show any hesitation. I’m wondering if it could be a metering lever issue. If it’s too high ,could that cause too much fuel and the saw to hesitate?

 

[J D]

It will make it hard to tune for sure

 

[mountainlake]

If you squeeze the throttle real fast and it dies it still lean, if it accelerates slow and takes it time to rev up it would be too rich. Steve

 

[Fatherwheels]

Just give it more on the low end, make sure your not four stroking
like crazy, too much on the high jet will interfere slightly with the low
and the other way around.
You should be able to get rid of the hesitation by upping the low,
your obviously very close as you are,
If this doesn't work, then metering valve may need checking.
A stiff diaphragm should also be replaced.
And make sure the saw has a few seconds to warm up, a slight
momentary bog on a cold saw on a cold day is acceptable until it warms,
and should clear after four or five throttle pulls / blips.
Make sure your fuel filter is clean, and the fuel lines are good, not split
in the tank or collapsing under pull from being either split or like jelly.

 

[North by Northwest]

Just give it more on the low end, make sure your not four stroking
like crazy, too much on the high jet will interfere slightly with the low
and the other way around.
You should be able to get rid of the hesitation by upping the low,
your obviously very close as you are,
If this doesn't work, then metering valve may need checking.
A stiff diaphragm should also be replaced.
And make sure the saw has a few seconds to warm up, a slight
momentary bog on a cold saw on a cold day is acceptable until it warms,
and should clear after four or five throttle pulls / blips.
Make sure your fuel filter is clean, and the fuel lines are good, not split
in the tank or collapsing under pull from being either split or like jelly.

Also ensure full fresh tank of fuel , it effects the quality of the tune !

 

[Wood Doctor]

Motherboard said, "Make sure your fuel filter is clean, and the fuel lines are good, not split
in the tank or collapsing under pull from being either split or like jelly."
-------------------------------
Nobody said anything else about the fuel filter. Good call. Replace it.

 

[North by Northwest]

Mortherboard said, "Make sure your fuel filter is clean, and the fuel lines are good, not split
in the tank or collapsing under pull from being either split or like jelly."
-------------------------------
Nobody said anything else about the fuel filter. Good call. Replace it.

Fuel filter inspection & replacement is the 1st priority along with the initial air filter inspection prior to any attempt to tune a saw properly . Also over looked quite often in saws that are hard to tune after a carb cleaning & carb kit , is the actual jet seating . I have had friends attempt a proper tune & get frustrated , when the jets or seats are worn beyond spec . A lot of good recommendations forwarded !

 

[FlyingDutchman]

I had a saw with a pinched impulse line once that had kind of similar issues.

 

[Old2stroke]

If the saw can be tuned to run properly when cutting at full throttle where it's using maximum fuel, The filter is NOT a problem. Usual causes of hesitating off idle are a low speed (L) set too lean or the transfer ports behind the throttle plate blocked, usually 2 of them and sometimes have to be cleaned by removing the welch plug covering them. Spray carb cleaner into the L screw cavity and see if it comes out all 3 ports of the idle system. Sometimes a faulty main jet check valve can cause bogging but it should also screw up the ability to get a consistent idle.