HELP! 572 idles bad and won’t rev up

[Yellowking86]

I bought a 572 on marketplace and it idles if I press the throttle slightly but won’t rev up at all and seems like it floods at idle and does. I put a new carb rebuild kit in it and spark plug and filter.

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[huskihl]

Couple things. Check the plug and wire. Make sure the crank case bearings are good so that the flywheel can’t wobble. Check the blue and red ignition wires from the coil to the carb for breaks or shorting out against the casting. Remove the flywheel and make certain the key isn’t sheared. If those are good, it’s possible that the nozzle in the venturi is bad and it’s also possible that the coil is bad

 

[Yellowking86]

I will check those thank you

 

[Poleman]

I would check and clean the carb first. If it’s a used saw the inner screen is probably dirty. I’ve see a lot of fines getting through the filter in those saws. In doing that you will be separating connections make sure they’re clean. Also like mentioned check crank bearings and seals, especially if the saws has a lot of use. I’ve seen three recently with bad bearings which took out the P/C and spun bearings in the case.
Big three… dirty carb, bad coil, bearings and seals on those saws. I’m dealing with Loggers saws that very little maintenance, poor fuel and run hard ever day.

 

[Yellowking86]

Bearings seem fine, I cleaned the carb and out a new diaphragm in it. I checked to e flywheel for a sheered key. Maybe it’s the nozzle. Seems like it loads up at idle and dies and when I pull the throttle all the way it makes and awful sound.

 

[Yellowking86]

Did you pull the H&L needles and inspect them, as well as their seats?

I did not, I will check those out thank you

 

[srcarr52]

Did you pull the H&L needles and inspect them, as well as their seats?

It's an Autotune saw, there are no H&L screws.

 

[Yellowking86]

the carb won’t hold pressure, sounds like it’s coming from the nozzle?

 

[EFSM]

the carb won’t hold pressure, sounds like it’s coming from the nozzle?

The metering chamber should not have pressure in it when testing. If it does, then the needle is leaking. Make sure you have the tester hooked up to the pickup fitting.

 

[huskihl]

the carb won’t hold pressure, sounds like it’s coming from the nozzle?

Make sure you’re checking on the right port. The one on the bottom right of the carburetor is the fuel supply for pressure testing. EFSM already mentioned it, but that puts pressure against the bottom of the needle and lever. It should hold about 15 psi. It’ll probably hold more like 30 being a newer EPA saw.

You can also do a vacuum test on the purge bubble side of the carb where the S shaped hose goes. If it won’t hold vacuum, I believe it is coming through the nozzle and shouldn’t be. I’ve never done it, but I’ve heard of others on here doing it and it makes complete sense to me

 

[Stump Shot]

Correct on the place for pressure testing.
Even 7 PSI is plenty for leak testing, I haven't found it necessary to check for pop off pressure. However, to vacuum test the impulse side, the fuel inlet needs to be blocked/clamped off first, or it will definitely leak through it. Just enough vacuum to be present is enough as long as it holds. What this tests is the flapper valves on the fuel pump diaphragm. If they deform, they can't hold the fuel back like they are supposed to. I can say from prior testing, this will cause a run issue when it fails. Also, this isn't something we dreamed up, I found it in one of Husqvarna's repair manuals for one of the 5 series, which for those folks out there who are interested, can be downloaded for free from HLSupply. This will give you the straight dope and not lead you astray like the internet videos and social media posts can do.
Some examples...
If I can do a small rant while I'm at it, there isn't anything on an autotune carburetor that can't be corrected as any other carburetor would be. In other words, when a 5 series isn't running right, a computer download isn't going to correct the problem inside the carburetor for you. You're going to have to get your hands dirty.
That felt so good I'll go on to rant 2. On older 562 and 550 type saws with the older style metering diaphragms in them, do not cut the inlet lever spring short to try and let the carb supply fuel again, replace the crispy old diaphragm with a new one. This will restore proper fuel delivery throughout the rpm range and eliminate any bogging etc. happening. Newer saws have the spiral diaphragm in them, which took care of the problem.
Best of luck @Yellowking86 getting your saw running right again. Hang in there, you'll get it.

 

[singinwoodwackr]

Correct on the place for pressure testing.
Even 7 PSI is plenty for leak testing, I haven't found it necessary to check for pop off pressure. However, to vacuum test the impulse side, the fuel inlet needs to be blocked/clamped off first, or it will definitely leak through it. Just enough vacuum to be present is enough as long as it holds. What this tests is the flapper valves on the fuel pump diaphragm. If they deform, they can't hold the fuel back like they are supposed to. I can say from prior testing, this will cause a run issue when it fails. Also, this isn't something we dreamed up, I found it in one of Husqvarna's repair manuals for one of the 5 series, which for those folks out there who are interested, can be downloaded for free from HLSupply. This will give you the straight dope and not lead you astray like the internet videos and social media posts can do.
Some examples...
If I can do a small rant while I'm at it, there isn't anything on an autotune carburetor that can't be corrected as any other carburetor would be. In other words, when a 5 series isn't running right, a computer download isn't going to correct the problem inside the carburetor for you. You're going to have to get your hands dirty.
That felt so good I'll go on to rant 2. On older 562 and 550 type saws with the older style metering diaphragms in them, do not cut the inlet lever spring short to try and let the carb supply fuel again, replace the crispy old diaphragm with a new one. This will restore proper fuel delivery throughout the rpm range and eliminate any bogging etc. happening. Newer saws have the spiral diaphragm in them, which took care of the problem.
Best of luck @Yellowking86 getting your saw running right again. Hang in there, you'll get it.

The 5-series whisperer has spoken...

 

[EFSM]

What this tests is the flapper valves on the fuel pump diaphragm. If they deform, they can't hold the fuel back like they are supposed to. I can say from prior testing, this will cause a run issue when it fails. Also, this isn't something we dreamed up, I found it in one of Husqvarna's repair manuals for one of the 5 series

I’m having a hard time figuring this out. Plugging the inlet and then vacuum testing shouldn’t tell anything about the valves, since they are positioned to let fuel into the metering chamber. Maybe I’m misunderstanding you.

You're going to have to get your hands dirty.
That felt so good I'll go on to rant 2. On older 562 and 550 type saws with the older style metering diaphragms in them, do not cut the inlet lever spring short to try and let the carb supply fuel again, replace the crispy old diaphragm with a new one. This will restore proper fuel delivery throughout the rpm range and eliminate any bogging etc. happening. Newer saws have the spiral diaphragm in them, which took care of the problem.

I have worked on some newer saws with the spiral diaphragm that had to have some coils cut off the spring in order to transition properly. I made the mistake of first replacing the spring with a softer one, but then it overfueled in warm temperatures.

 

[Stump Shot]

I’m having a hard time figuring this out. Plugging the inlet and then vacuum testing shouldn’t tell anything about the valves, since they are positioned to let fuel into the metering chamber. Maybe I’m misunderstanding you.

I have worked on some newer saws with the spiral diaphragm that had to have some coils cut off the spring in order to transition properly. I made the mistake of first replacing the spring with a softer one, but then it overfueled in warm temperatures.

Yes, they let fuel in, they also don't let fuel out once it gets in there.

 

[singinwoodwackr]

Yes, they let fuel in, they also don't let fuel out once it gets in there.

Hotel California version?

 

[Stump Shot]

Hotel California version?

I guess that's one way of looking at it the situation. Lol

 

[EFSM]

Yes, they let fuel in, they also don't let fuel out once it gets in there.

The only way I know of to check the pump valves is to put a vacuum on the inlet with the metering needle removed.

 

[Stump Shot]

The only way I know of to check the pump valves is to put a vacuum on the inlet with the metering needle removed.

Now you know another, the Husqvarna way.