Echo CS-590 wont idle, scoring on new piston. Air Leak?

[telecasterfool]

Get a different carb. sometimes swapping will tell you things. 590 carbs are everywhere. Check the impulse port. Somewhere between the impulse from the cylinder-impulse line-small diaphragm in the top of the carb-screen-check valve-large diaphragm-- you are not getting enough fuel. It's like a fuel pump in an old V8. Can you keep it running at idle by dripping or squirting fuel in the carb?
when it dies at idle, immediately take the spark plug out - wet or dry will tell you if it's not enough or too much fuel. good luck.

 

[9050lx]

Check base of cylinder.I replaced a 590 piston, could not get a good idle until reapplying threebond on the base.Also replaced the check valve.

 

[freebilly]

Get a different carb. sometimes swapping will tell you things. 590 carbs are everywhere. Check the impulse port. Somewhere between the impulse from the cylinder-impulse line-small diaphragm in the top of the carb-screen-check valve-large diaphragm-- you are not getting enough fuel. It's like a fuel pump in an old V8. Can you keep it running at idle by dripping or squirting fuel in the carb?
when it dies at idle, immediately take the spark plug out - wet or dry will tell you if it's not enough or too much fuel. good luck.

Thanks for taking the time to read the symptoms and what I have done and respond with something useful. Swapping the carb is the only thing left to try. It will stay running if I drop fuel Into the carb at idle or if I really back out the low needle.

 

[freebilly]

Freebilly, if you only paid 30 bucks for the saw , you are in good shape, except for the time and some other money you put in it. I would buy a new saw .. Keep the bar cause that will wear out someday so you already have a spare. The loop is worth 20 bucks.. You also have new spare parts .. I see it this way cause I hate working on tools though.

I work on and build saws for fun. The fact that I’m only in 30$ makes me want to fix it even more because there is wiggle room and still make profit on a flip. I posted because I am stumped and enjoy working on my tools. Thank youb

 

[telecasterfool]

Thanks for taking the time to read the symptoms and what I have done and respond with something useful. Swapping the carb is the only thing left to try. It will stay running if I drop fuel Into the carb at idle or if I really back out the low needle.

Check the impulse line - it moves the diaphragm within the carb that pumps fuel. Also check the metering lever height. Check that the proper needles are in the Hi and Low sides - that happened to me once. I can't remember if they are different in that carb.

 

[huskihl]

How many turns out on the L to get it to idle?

 

[freebilly]

Check the impulse line - it moves the diaphragm within the carb that pumps fuel. Also check the metering lever height. Check that the proper needles are in the Hi and Low sides - that happened to me once. I can't remember if they are different in that carb.

Impulse line is working well and air tight. Metering level is good needles are in the right spot but low needle has a very slight bend in it. I think this is more than likely my issue. Seems to be the last option as well. New carb is on its way this week. I will keep this thread updated

 

[freebilly]

How many turns out on the L to get it to idle?

It will start on 1.5 turns but stumbles and dies after a few seconds then requires choke to restart. At about 3 turns out it will idle rough. Still even then only idles for 20-30 seconds before slowing down and dying.

 

[freebilly]

Check base of cylinder.I replaced a 590 piston, could not get a good idle until reapplying threebond on the base.Also replaced the check valve.

Bottom of cylinder was sealed with motoseal and checked with soapy water at 7psi. She’s air tight

 

[9050lx]

Sounds like starving for fuel. big air leak, or carb plugged somewheres?

 

[mountainlake]

I've had to replace the boot between the carb and cylinder on a couple of them. Steve

 

[huskihl]

It will start on 1.5 turns but stumbles and dies after a few seconds then requires choke to restart. At about 3 turns out it will idle rough. Still even then only idles for 20-30 seconds before slowing down and dying.

OK. I was thinking it would keep running if you turned it out further. Many of the new EPA carburetors require between 2–4 turns out on the jets at their normal setting. Just making certain you weren’t trying to get them to run at the old normal 1 turn out that worked for decades. New stuff isn’t like that

 

[cscltd]

Could be plugged carb from sitting that kit will not cure, may need sonic cleaned or new carb. These new carbs do not like to be sitting with old fuel left in them.

 

[Gord404]

It is also easy to mistake the 4 stroking for the rev limited coil on that saw- thought it was lower than 12,500

 

[huskihl]

It is also easy to mistake the 4 stroking for the rev limited coil on that saw- thought it was lower than 12,500

If it’s that low, that could’ve been the problem the whole time. Tachs go wonky when approaching the rev limiter on a coil and will not read correctly. It could easily have been tuned to the equivalent of 14 K but was rev limited to 12. If the motor wasn’t designed to turn 14 K, it would definitely score

 

[freebilly]

Sounds like starving for fuel. big air leak, or carb plugged somewheres?

I agree. She’s air tight as far as I’m concerned. Takes almost 5 mins to drop 1psi when pressure testing.

If it’s that low, that could’ve been the problem the whole time. Tachs go wonky when approaching the rev limiter on a coil and will not read correctly. It could easily have been tuned to the equivalent of 14 K but was rev limited to 12. If the motor wasn’t designed to turn 14 K, it would definitely score

cs-590 coil is limited at 13,500. Pretty confident in my ear to recognize 4-stroking vs limiter and spark plug was wet after running

 

[freebilly]

It is also easy to mistake the 4 stroking for the rev limited coil on that saw- thought it was lower than 12,500

From what I’ve read, cs-590 is limited at 13500

 

[stihltech]

At this point, you are looking at a new carburetor. The only thing left to try is a high speed jet nozzle in the carburetor IF it is replaceable.
Saws that sit are harder to repair than daily run saws. Old fuel is just eating away at the carb the whole time.
When I get a saw in the shop that has been around 5 years or more and looks like new because "it hasn't been used much" its a red flag. 3/4 of those saws will have a fuel system issue, I don't care what fuel you are using. Fact of 2 cycle repair.

 

[telecasterfool]

I would like to comment on the piston scoring due to high end lean condition. The OEM carb on cs-590 has an extra fuel "nozzle" on the high circuit. It has been well documented on this site. I believe it is difficult to lean these saws on the high end. IF, the carb is in working order...

 

[huskihl]

I would like to comment on the piston scoring due to high end lean condition. The OEM carb on cs-590 has an extra fuel "nozzle" on the high circuit. It has been well documented on this site. I believe it is difficult to lean these saws on the high end. IF, the carb is in working order...

I believe it’s just an auxiliary jet that flows x amount of the required fuel all the time, and then the needle lets in the rest. Like many epa carbs today.