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Echo CS400 tuning after muffler mod questions

redlined_b16a

redlined_b16a

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14 year old saw......its been a reliable lil saw.
Hurricane Ida layer over 40 plus inch oaks and the CS400 struggled.
Ordered a CS590(Love it) but I wanted to get a lil more from the CS400
Gutted 70% of the muffler and enlarged the exhaust hole
Removed the carb fuel needle restriction caps and I read on several threads here to start at 3.5 turns CCW from closed.

Well fire's up but runs rough(too rich)
I have to turn it CW about 2 turns before it leans out and runs well.

Has plenty more power but is now a Gas Hog.
Also I'm 14 feet above sea-level
Is that why my saw requires a leaner tune then all the rest of the turns I read that state 3 1/4 or 3 turns is near perfect?

I dont want to damage my saw.
In 14 years I have only changed the primer bulb and pull rope,filter and plug.
And of corse bars and blades.
Highly dependable saw.

How do I know if I'm running to lean?
Is it just going to be a gas hog from here on out?
Full tank use to last 40 or so minutes same as the oil tank
now I run two tanks of fuel per 1 tank of bar oil in 40 minutes.
Thanks in advance.
 
Big_6

Big_6

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Why wouldn't you turn your L to reduce your idle speed?

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redlined_b16a

redlined_b16a

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Why wouldn't you turn your L to reduce your idle speed?

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I tried that.
What I found was the housing that holds the choke and primer bulb lowers the idle when pressed on.
Was thinking I have something incorrect on instalation.

I'm new to tuning saws
 
Cliff R

Cliff R

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Not exactly sure what occurred with your CS-400 but I've removed the CAT from dozens of CS-370/400's and opened up the holes slightly in the "can" around it, and the exit just a tad and never ran into any tuning issues or had to deviate much from the stock settings. If you've turned it into a big guzzler I suspect other issues or you may want to obtain another muffler and start over. Less is more when it comes to modifications with mufflers, and other things related to improving air flow thru the engine. The coils have a timing retard module (rev limiting) feature so they can be a little tricky to tune correctly.

Set the "L" screw first, highest/smoothest idle speed then just a tad CCW till it slows every so slightly. Set the "H" speed screw noticeably rich and "four stroking" pretty hard. Start making some cuts till it cleans up nicely and best power. The retard module mimics a correct "H" speed screw setting so er a tad rich vs a tad lean and you'll be fine there.

These are NOT high RPM saws, but grunt well for the cc's and a nice broad/smooth/flat power curve. So don't shoot for really high RPM's in the cut, you aren't going to find it. Tune for grunt and mid-range power, plenty of it there and those little saws are very well built and will last for decades with the right tune in them. Hardly a day goes by I'm not running one of mine, just last night cut a nice load of limbs for the fire pit on the back porch.......
 
redlined_b16a

redlined_b16a

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A little update.
I been really busy cutting with the new CS590(what an animal)
Adjusted the low speed needle and got the idle down on the CS400 but haven't used it yet.
Hurricane Ida took out alot of trees in my yard and put a 100 foot oak across the house.

Appreciate the help.
Wondering how badass the 590 would be with the muffler mod....
 
Cliff R

Cliff R

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The L screw is NOT used to control idle speed, it's for idle mixture. The idle speed screw controls idle RPM.

If idle RPM is not controllable via the idle speed screw, you may have a leak someplace in the intake system......

The CS-590 doesn't need much of a "muffler mod". Just open up the deflector a bit and for sure remove/modify the mixture screws. I ran a thread or responded to several threads on that that should be available if you do a search. If not I can put them back up here if/as needed.......
 
redlined_b16a

redlined_b16a

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The L screw is NOT used to control idle speed, it's for idle mixture. The idle speed screw controls idle RPM.

If idle RPM is not controllable via the idle speed screw, you may have a leak someplace in the intake system......

The CS-590 doesn't need much of a "muffler mod". Just open up the deflector a bit and for sure remove/modify the mixture screws. I ran a thread or responded to several threads on that that should be available if you do a search. If not I can put them back up here if/as needed.......
After the cs400 muffler mod the idle was high.
The L screw actually did lower or raise the engine idle speed.
 
Cliff R

Cliff R

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Something happened because opening up the muffler would not cause any of the symptoms or issues you are seeing, especially an increase in idle speed that can't be controlled without using the "L" speed screw to slow it down.......
 
redlined_b16a

redlined_b16a

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Something happened because opening up the muffler would not cause any of the symptoms or issues you are seeing, especially an increase in idle speed that can't be controlled without using the "L" speed screw to slow it down.......
I had issues with the fuel hose being pulled off of the primer bulb br the throttle linkage rubbing against it.
I'm thinking the bulb/kill switch mount isn't sitting correctly.
 
Cliff R

Cliff R

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If you can close the carburetor throttle plate all the way then the engine would stall out. It's getting air someplace if/when this happens. A very small leak shows up as loss of control of idle speed.....
 
Cliff R

Cliff R

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The "L" speed screws is used to find the ideal A/F ratio at idle. There is a tiny hole exposed just in front of the throttle plate at idle speed. This supplies idle fuel. Another hole or holes (often transfer slots on larger carburetors) are located just past the throttle plate position at idle to provide fuel to prevent hesitation/stumble/bog right off idle. The additional ports plus the correct setting of the "L" speed screw are there to provide the ideal A/F ratio to sustain idle speed, and adequate fuel to cover up a potential lean condition right off idle. Most of these carburetors do not use an accl pump so the setting of the "L" speed screw is critical to correct engine function.

The "L" speed screw is NOT used to adjust idle RPM, but idle RPM will vary considerably as you go from rich to lean (speeds up), then slows down if you go either too lean or too rich past the ideal adjustment.

I'd find your leak or other issue causing the loss of speed control with the idle speed screw, then adjust the carb to the correct settings.........
 
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