Husqvarna 572 starts but dies

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The mityvac i have the gauge goes up to 30 psi,the carb was holding 20 psi no problem.I tried pumping it up beyond 30 psi,it was not popping but slowly loosing pressure at that point.Not sure if this was the hose leaking or needle valve not leaking.Will repeat the test when I get the saw back and if its not working. If the pop off pressure is too high,would not the fuel pump have a problem to pump enough pressure to pop the needle valve?Just a thought.
For modern carbs pop-off pressure is pretty much irrelevant. All it needs to do is hold off the fuel pump pressure which is less than 10PSI. Pressurizing a carb to more than 10 PSI can do damage to the fuel pump diaphragm.
 
I got a confirmation that the saw is ready to be picked up.It went in for the threads repair,but they were to do a quick diagnostics on the autotune.Perhaps its working or then maybe not,will be at least a week before I have time to pick it up.

The mityvac i have the gauge goes up to 30 psi,the carb was holding 20 psi no problem.I tried pumping it up beyond 30 psi,it was not popping but slowly loosing pressure at that point.Not sure if this was the hose leaking or needle valve not leaking.Will repeat the test when I get the saw back and if its not working. If the pop off pressure is too high,would not the fuel pump have a problem to pump enough pressure to pop the needle valve?Just a thought.
How many hours is on it?
 
Hours unknown but I expect alot.The shop is supposed to check the hours so will know when i pick it up.
 
The mityvac i have the gauge goes up to 30 psi,the carb was holding 20 psi no problem.I tried pumping it up beyond 30 psi,it was not popping but slowly loosing pressure at that point.Not sure if this was the hose leaking or needle valve not leaking.Will repeat the test when I get the saw back and if its not working. If the pop off pressure is too high,would not the fuel pump have a problem to pump enough pressure to pop the needle valve?Just a thought.
The fuel pump just delivers fuel to the inlet valve, it is NOT supposed to provide enough pressure to open it, the opposite is true, the valve should stay closed until it is opened by the main diaphragm pressing against the control lever.
 
I read a bit about diaphragm carbs and it seems you are correct.Couple of questions

Is there a spec for the metering lever height?I believe the autotune carb is made by zama?All the issues point to the fact that it is not pumping any fuel or does so intermittenly.Its possible the saw has been fiddled by someone prior to me.I think i will order a carb overhaul set(membranes) but would avoid to buy a needle valve/metering arm since it is holding pressure.

Could the primer bulb or leaking return hose between bulb and carb cause running issues?
 
I had a motor(not chainsaw) with a walbro diaphragm carb.It would idle and start fine but die when given throttle.Found the specs and adjusted the metering arm,it was off by 1mm.Adjusting it did nothing to the idle(still fine) but it corrected the lean condition that caused the bog at wot.The arm was set too low and caused a lean condition,but it would still idle nicely.Therefore I dont think I have the same issue on this autotune carb but its worth a check.
 
That probably won't apply to the autotune carb though?
Might / might not. Metering height is specific to a given carburetor model. You need to find the specs for your particular carb. The model should be cast/etched into the carb body somewhere. Note that there are multiple settings on the pictured Zama "Z" gauge.
 
Could the primer bulb or leaking return hose between bulb and carb cause running issues?
Usual problem with primer bulbs is someone has screwed with plumbing and got it wrong, the bulb is supposed to suck fuel from the carb and dump it back into the tank. There are check valves in the primer that prevent fuel or air from being drawn back into the carb so as long as these are OK and the line between the carb and the primer is good, they should not cause running issues. A good test is to remove the primer line from the carb, push a small ball bearing in the end and reinstall it on the carb to completely block the primer system, in operation you will just have to pull the starter cord a few more times to get it started but you will KNOW the primer is having no affect.
 
Got saw back.Still not idling or run on part throttle.Will run on wot like a scolded ape.Needs choke to get it started.Ran it at wot for a reset as suggested and shown in videos,this had no effect.

Dealer refused to reset autotune,said its not necessary,said it will adjust itself.Well how is it going to tune itself if it cand idle for longer than 2 seconds?
At least they updated the firmware and gave me a printout.fault code 13 has ocurred 255 times

Plumped of the fuel return/primer bulb,had no effect.
I gave it gas from a torch on idle and that way it will keep on running.IMG_20210506_151950.jpg

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I also checked the metering height and the arm is flush with the seal surface of the carb. The idle value 40 seems low to me,then again there seems to be no factory values to check up on or compare to.Whatever the issue may be,when this saw is running its getting sold of and replaced by a saw with a manual carb.Words do not describe how pissed of i am with this piece of junk.
 
So i took the carb off again,took the autotune unit off the carb,no dirt that could see of.
IMG_20210506_205459.jpg
 
There is the holes for the sutotune unit.The left one goes straight to the metering chamber.The right one is the fuel return,goes to the brass nipple.Spraying the middle one it will come out of the 3 small holes in the aluminium body next to the butterfly,it will also come out of the brazz nozzle inside,i assume this is the fuel feed at wot.

All passages in carb seems open,seems like the autotune solenoid is not working
 
Spraying the middle one it will come out of the 3 small holes in the aluminium body next to the butterfly,it will also come out of the brazz nozzle inside,i assume this is the fuel feed at wot.
This would be the L circuit.
Don’t know if it’s been mentioned in here yet or not. I’d remove the brass nozzle that protrudes into the venturi and see if it still passes air only one way like a check valve
 
How could that brass nozzle be removed?I dont see how it could be removed.I did test the return fuel nipple from the carb and that held vacuum.

But there is only one port in the autotune that will feed bot low and high speed?Is there only one solenoid in the unit too?
The low speed value 40 is from what i have understood very rich,yet the carb is not delivering any fuel at idle/low speed.
 
This would be the L circuit.
Don’t know if it’s been mentioned in here yet or not. I’d remove the brass nozzle that protrudes into the venturi and see if it still passes air only one way like a check valve
I think you may be on to something here.

So i can get it to idle by giving it manually fuel by a map torch,i can also get it to idle by almost closing the choke.Im not 100% sure on this but the lower the value on the high/lo autotune settings the more fuel its trying to deliver.In my case the value is very low(40),its trying to deliver more fuel but its not getting any of it.At idle/low speed its supposed to pull fuel from the three small orifices because of the vacuum,the main nozzle check valve is supposed to be closed.But if the main check valve is leaking it will pull air into the circuit.The bad thing is that this check valve cant be bought,i found a part number for it from zama,its unigue and cant be found anywhere online.

Fuel to both the high and low are from the same port of the at unit,the same solenoid adjust fuel by opening and closing a solenoid valve.So if the saw is delivering fuel at wot then the solenoid must be working and thus the problem cannot be the electronics of the carb.autotune5.jpgerror 2a.JPGINTERNET POST PIC NO.557b Large Web view.jpg
 
Spent the day spraying the carb with brake and carb cleaner and testing.
Fuel inlet blocked,vacuum on return nipple.It will not hold,the gauge will slowly creep to zero.Not sure how well it supposed to hold vacuum,since it will draw air from the 3 idle holes.
Removed the autotune unit and vacuum testing the port that feeds the idle/wot circuit.Its a bit hard to get the tool to seal against the flat surface so its not really scientific.But it would not hold vacuum,slowly creeping to zero.I then put some tape over the idle holes,not sure if they sealed properly,but it was loosing vacuum alot slower,sprayed brake cleaner on the main nozzle,then it would hold the vacuum for maybe 10 secs and then start creeping slowly.
It was a bit hard do test anything properly since it was hard to get everything to seal,but I came to the conclusion that the main nozzle is leaking some,but not alot.Like it will drop from 15psi to 0 in a minute or more.

So I put everything back together and the saw runs perfectly,let it idle for 5 minutes to let the idle adjust itself.Made some cookie cuts for wot adjusting,it runs perfectly.Idle speed is low but that seems in line with what ive read and see on the tube,returns nicely to idle after a cut.One pull starts hot/cold

Its truly is a beast when it runs,obnoxiously loud too.Not even my ported& muffler modded 357 comes close to loudness.Still I just cant see myself using and trusting this saw or any autotune for that matter.Even less when i know repairing requires a dealer and service cost is way too expensive.Will sell it and get a 372 or a new echo instead.Being a xpg its also quite heavy compared to a old school 372.
 
For those going tru this thread, here is a forced tune done on a 555 that sat for a long time and would not idle. Kind of a noticeable change. While this 572 from the op may have different issues, often a simple forced tuning as shown here will solve what seems like dire issues

 
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