CS-590 will not idle

[Dave41A]

Good afternoon:  This is my first post here at the Forestry Forum.  I'll apologize in advance for what is a long first post.  I have had a CS-590 for about 5 years.  Is has been a good saw, but hard to start when hot.  However, now it will start but not idle.  It will also not run wide-open, but instead bogs dies and dies upon squeezing the throttle.  This is actually an improvement from a few days ago, when it would not start at all. 
 
I will summarize what I have done:  fresh gas, cleaned & gapped sparkplug, checked for spark (good), removed and cleaned carburetor (including removing rubber diaphragms and probing jets with a fine wire).  While I had the carb off, I noticed that the choke linkage at full choke is supposed to also set the throttle to about one-quarter, which should stay that way until the gas lever is squeezed & released.  Mine would do this nicely off the saw (and make a nice "click" when set) but the choke lever would hit the front side of the air cleaner housing when installed on the saw—preventing it from going to full choke and not staying there (which explains the hard hot starts).  I installed a thin gasket as a spacer between the carb and this air cleaner housing which now allows the choke to apparently function properly with 1/32 inch extra room:  At full choke the throttle is "set," and at stays there when pushing the choke off.  Squeezing the gas releases the throttle back to idle.  Now, when cold,  it will fire after 1-2 pulls at full choke, and fire up in 2-3 pulls, and run at a fast idle (chain moving) while it remains at "half choke" (the throttle linkage keeps the choke from fully opening until the gas lever is squeezed, even if the choke is "off"). 
 
However, even if I allow the saw to warm for a good 30 seconds, upon squeezing the gas lever, the saw will immediately die.  If I squeeze and hold, it will die.  If I squeeze and release, it will die.  I have removed the carb screw limiters and back off the L screw as described in video posted here by Andyshine77 for the CS590.  Following another video also posted by the same person, I have backed the L screw out two full turns and the saw still will not idle.  After it dies it starts right back up again reliably and runs until I squeeze the gas lever again.
 
Like many others here, I am stuck at home with the virus measures, so taking it to a repair shop or dealer is not an option for the near future—they are all closed anyway.  The saw has maybe only a few months left on its warranty; I would like to learn how to fix it as I hope it will last me a lifetime. 
 
I cut about 3 cord a year for firewood but now have a band saw so will be cutting significantly more as I am trying to build a barn.  I am at about 1000' above sea level—it is mid 40's outside.  I had been running 90 octane, ethanol-free gas; now am on 87 regular as that's what I have right now. 
 
I have experience working on other gas-powered equipment (mostly tractors) and have been using chain saws for 25-30 years or so, but have much less experience fixing them than tractors.  I've posted this question over at my usual forum (yesterdays tractors) but have not gotten very far with the responses, as the experience base there is very different from what I see here.  I can post pictures or additional details if required.  
Thanks in advance for your help.  Any suggestions are appreciated.  Dave 

[dougand3]

Welcome. Plenty of good data in your post.
Did you change the carb diaphragms? New diaphragms are in order.
Check that muffler screen is not blocked with carbon.

[Dave41A]

Welcome. Plenty of good data in your post.
Did you change the carb diaphragms? New diaphragms are in order.
Check that muffler screen is not blocked with carbon.

The muffler screen looks clear.  I did not change the diaphragms--I put the originals back in.
I am happy to order a set if that will fix things.  As I noted, I am not experienced with chainsaw troubleshooting.  Is what I describe typical for a saw with worn-out diaphragms?
Thanks for the response & welcome.  Dave

[sawguy21]

Welcome!! Changing the diaphragms is cheap and one less thing to worry about. Also check the fuel line, it should be pliable but not spongy, and change the in tank filter.

[Dave41A]

Welcome!! Changing the diaphragms is cheap and one less thing to worry about. Also check the fuel line, it should be pliable but not spongy, and change the in tank filter.

Thank you.  I am new to chainsaw repair, and will put some diaphragms in order.  However, are diaphragms something that I can typically only expect 5 years of use from?  The fuel line seems fine--not spongy.  The in-tank filter is also the original.

[dougand3]

5 years is a long life for a diaphragm. Change the pickup (fuel filter).

[Hilltop366]

Sounds like a carb low speed circuit issue. It will be either getting too much fuel or not enough.

Did you remove the the fuel mixture screws when cleaning the carb? 

When cleaning out a carb I will take a can of wd40 and using the nozzle tube spray in each circuit and watch in the carb barrel to make sure there is flow in all the places it is suppose to and confirm that there is no blockage.

Wear eye protection.

[Dave41A]

5 years is a long life for a diaphragm. Change the pickup (fuel filter).

Thank you.  This is the kind of information I need to hear and learn.  My experience with saws to date has been either "homeowner" saws where the diaphragm outlasts the saw, or with my Father's old craftsman (1980's vintage) that still runs awesome, and I have never done anything to it!  I'll order a spare diaphragm set and keep it on hand for when the next time comes.

[Dave41A]

Sounds like a carb low speed circuit issue. It will be either getting too much fuel or not enough.

Did you remove the the fuel mixture screws when cleaning the carb?

When cleaning out a carb I will take a can of wd40 and using the nozzle tube spray in each circuit and watch in the carb barrel to make sure there is flow in all the places it is suppose to and confirm that there is no blockage.

Wear eye protection.

I did not remove these screws, and stopped loosening the L when I did as I was afraid of backing the screw out and never being able to get it back in for some unknown-to-me reason.  I take it that I can remove these screws, clean inside & blow WD-40 through as you describe, then re-assemble without difficulty?  Thank you for your response.  Dave

[Hilltop366]

Yes they can be removed, usually first I will turn them in until they lightly seat fully while counting how many turns it takes to get there, record the number of turns (eg  H=1½ or L=1¼) then remove.

Then when you put them back in screw them in until they seat again and back out the recorded number of turns.

When flushing out and checking passages put your finger over the H and L holes and put the spray tube in the holes that feed the circuit on the metering side of the carb (under the metering diaphragm) and watch for the fluid to come out in carb barrel checking to see if it comes out the holes. If any are restricted they can usually be cleaned out with a small piece of wire, I like to use brass wire from a brush or copper from a multi strand wire. then test again.

If you have new diaphragms you might as well put them in but 5 year old ones should be ok unless they had gas dry up on them and feel stiff, in a pinch I have cleaned them off before by rubbing them with my fingers and/or finger nail to "loosen" them up, check to make sure the 2 fuel pump diaphragm flaps lay down flat on the carb body too.

[Dave41A]

Yes they can be removed, usually first I will turn them in until they lightly seat fully while counting how many turns it takes to get there, record the number of turns (eg  H=1½ or L=1¼) then remove.

Then when you put them back in screw them in until they seat again and back out the recorded number of turns.

When flushing out and checking passages put your finger over the H and L holes and put the spray tube in the holes that feed the circuit on the metering side of the carb (under the metering diaphragm) and watch for the fluid to come out in carb barrel checking to see if it comes out the holes. If any are restricted they can usually be cleaned out with a small piece of wire, I like to use brass wire from a brush or copper from a multi strand wire. then test again.

If you have new diaphragms you might as well put them in but 5 year old ones should be ok unless they had gas dry up on them and feel stiff, in a pinch I have cleaned them off before by rubbing them with my fingers and/or finger nail to "loosen" them up, check to make sure the 2 fuel pump diaphragm flaps lay down flat on the carb body too.

Thank you very much for continuing to respond.  I have removed both adjustment screws and sprayed wd-40 into the screw holes as you describe.  I have also done it with the screws installed but with the metering diaphragm removed.  I can spray into the hole next to the Welch plug and into the brass plug/insert.  In all cases the WD-40 comes out all 3 idle holes/jets or the main jet, as appropriate (e.g. the right places).  I have reinstalled the carb, and began with both screws 1-1/2 turns out (Unfortunately, I did not record their initial settings as you describe).  It will fire on the first pull at full choke.  Then it will fire and run on the first or second pull with the choke in.  But as soon as I squeeze the throttle lever, it dies.  Every time.  I heave repeated this after backing out the L screw 1/4 turn at a time for 2 full additional turns (3-1/2 turns total) with no success.  New diaphragms are on order but the current ones look usable and are not stiff at all.  I can post pictures of the diaphragms but find it difficult to believe that their condition would degrade the saw's performance so much that it will not run at all.  Thanks again, Dave

[Dave41A]

Yes they can be removed, usually first I will turn them in until they lightly seat fully while counting how many turns it takes to get there, record the number of turns (eg  H=1½ or L=1¼) then remove.

Then when you put them back in screw them in until they seat again and back out the recorded number of turns.

When flushing out and checking passages put your finger over the H and L holes and put the spray tube in the holes that feed the circuit on the metering side of the carb (under the metering diaphragm) and watch for the fluid to come out in carb barrel checking to see if it comes out the holes. If any are restricted they can usually be cleaned out with a small piece of wire, I like to use brass wire from a brush or copper from a multi strand wire. then test again.

If you have new diaphragms you might as well put them in but 5 year old ones should be ok unless they had gas dry up on them and feel stiff, in a pinch I have cleaned them off before by rubbing them with my fingers and/or finger nail to "loosen" them up, check to make sure the 2 fuel pump diaphragm flaps lay down flat on the carb body too.

I will add that the idea of too much gas has also crossed my mind.  So I seated the L screw and backed it out 1/4 turn at a time.  It would fire every time, but not continue to run.  At about 1-1/4 turns out, it now fires and runs at partial throttle/half choke as I described.  But again, as soon as I touch the throttle lever, it dies.  Thank you again for your help.  Dave

[Hilltop366]

Does it run at any speed with the choke off?

I was thinking it would run at fast speed but die at low speed.

[Dave41A]

Does it run at any speed with the choke off?

I was thinking it would run at fast speed but die at low speed.

No. If I squeeze and hold the throttle, it dies.  If I squeeze and release, it dies.  Anything that disturbs the carb from a half-choke condition makes the saw stop running.  Thank you for continuing to work with me on this.  Dave

[Hilltop366]

Ok sorry about that, for some reason I was thinking it was a only dying at low speed. 

Did you check your fuel filter, with it removed you should be able to blow through where the gas line connects easily.

[Dave41A]

Ok sorry about that, for some reason I was thinking it was a only dying at low speed.

Did you check your fuel filter, with it removed you should be able to blow through where the gas line connects easily.

Yes.  If I do not loosen the fuel cap before removing the fuel line form from the carb, it will spill fuel all over the place from tank pressure pushing fuel up the hose.  I also tried running it once with the filter removed to see if that made a difference.  It did not.  
I can also blow backwards down the fuel line through the filter without difficulty.
Thank you again for continuing to respond.  This is very helpful even if it is still not running.  Dave

[Hilltop366]

Did you get the metering and pump diaphragm and gaskets back on in the correct order?

You can look up a parts diagram for the saw on line for a exploded view of the carb, there may be a serial number range specific to your saw.

 Does the needle move freely in the seat?

[Dave41A]

Did you get the metering and pump diaphragm and gaskets back on in the correct order?

You can look up a parts diagram for the saw on line for a exploded view of the carb, there may be a serial number range specific to your saw.

Does the needle move freely in the seat?

The needle does move freely in the seat.  The little spring in in place and looks to be in good condition.  
I will triple-check, but I am working from this parts diagram, and am pretty confident everything is in the right place (attempting to attach photo, link if that does not work)
Edit as of 8:46 PM:  I have verified that everything is in its place per the attached diagram.


Link deleted by Admin. as photo links not permitted

[Al_Smith]

Just a reminder of the fact every carb manufacture has a web site and in that web site lists not only IPL's but tuning tips .Such examples as why a saw bogs down on a throttle up ----just saying . ;)

[Dave41A]

Just a reminder of the fact every carb manufacture has a web site and in that web site lists not only IPL's but tuning tips .Such examples as why a saw bogs down on a throttle up ----just saying . ;)

Al:  Thank you for your response.  I have dug around a little at the walbro carburetor website.  I have not been able to find any tuning tips.  I also checked the echo-usa website with no success there either.  I also am not familiar with the abbreviation "IPL." 
If you could provide some guidance on where to look on these websites (I recognize there are limitations on posting external links), it would be appreciated.  Thank you!  Dave

[sawguy21]

IPL means iluustrated parts list.

[Dave41A]

IPL means iluustrated parts list.

Thank you!  I have seen the exploded diagrams, I am starting to wonder if the o-ring that forms the seal between the carb and the bellows that leads to the crankcase may be bad.  If there is a vacuum leak at this point, it would at least explain the inability to idle.  I had a tractor that would not idle and it was a leak on the intake side that was the culprit--it only became apparent during the high-vacuum situation during idling.  Would a thin layer of RTV or form-a-gasket like a Permatex 2B be out of order here?  I would need to be careful not to get any into the crankcase.
Visually this O-ring looks OK, but I am starting to think it is either that or the bellows themselves that is the source of the problem.
Thanks again, Dave

[Al_Smith]

In generalities when you go from idle to high speed operation if the idle jet is too lean the increase in pressure drop will suck up too much fuel from the idle circuit before the high speed kicks in.The idle jet is below the throttle butterfly and the high seed is above slightly .This seems to be more pronounced if the saw engine or whatever it is not warmed up .For example I have to partly choke my Stihl BG 85 blower for a few seconds because of this which although I should tune the carb better I just have not done so .

Actually believe it or not the idle jet will put out enough  fuel to run at speed without the aid of the high speed it just won't produce as much power ---usually .

[Dave41A]

In generalities when you go from idle to high speed operation if the idle jet is too lean the increase in pressure drop will suck up too much fuel from the idle circuit before the high speed kicks in.The idle jet is below the throttle butterfly and the high seed is above slightly .This seems to be more pronounced if the saw engine or whatever it is not warmed up .For example I have to partly choke my Stihl BG 85 blower for a few seconds because of this which although I should tune the carb better I just have not done so .

Actually believe it or not the idle jet will put out enough  fuel to run at speed without the aid of the high speed it just won't produce as much power ---usually .

Al:  Thank you.  I've been able to start and run the saw at "half choke," and have run it this way for 30 seconds or longer--as long as I don't touch the throttle.  I have done this repeatedly until the engine is good and warmed up.  However, as soon as I touch the throttle linkage, the engine dies.  If I squeeze and hold, it dies, and if I squeeze and release, it dies.  This linkage releases the choke from half-open to full-open, so for whatever reason, this saw only runs at half-choke.  I've backed out the L screw from closed to a full 3-1/2 turns open.  Below 1-1/4 turns open, it will not even run on half choke.  From 1-1/4 turns on up, it runs, but still only at half choke.  It does this with the air filter on and removed.  I am opening the screw 1/4 turn at a time.  Thanks again, Dave

[Hilltop366]

Where is your high speed (H) set?