550xp mk2 high reving problem

[edmxz2002]

I have a 2019 550xp mk2 that's revving high then stalling.
Cold start, choke for 3 pulls, shut choke off pull 1 or 2 pulls it starts. Runs a little rough. Blip the throttle and it either dies right away or the rpm's race up to full throttle for 3 seconds then dies.
I have read about setting the auto tune by idling for a few minutes then running at full throttle while dragging the chain down a log. I can't do that because it won't go to idle and goes full throttle with the trigger released.
Things I have chaced include removing the muffler and checking piston. It looks perfect. Removed carburetor and opened it up and cleaned it. It looked spotless and the diaphragm and gaskets are in good condition. Held 10 psi for over 5 minutes when checked from the end of the fuel line in the tank.
I checked compression and got 120psi on my gage that I know reads low.
I removed the clutch, oil pump and flywheel to get a look at the crank seals. I think I am looking at the bearing? Not like crank seals I have replaced or seen on other saws.
I have a vac/pressure tester but I don't have anything or anyway to block the intake.
Any ideas or directions on what I should check next?

Any help will be greatly appreciated.
TIA.

 

[Timber MacFallen]

I have a 2019 550xp mk2 that's revving high then stalling.
Cold start, choke for 3 pulls, shut choke off pull 1 or 2 pulls it starts. Runs a little rough. Blip the throttle and it either dies right away or the rpm's race up to full throttle for 3 seconds then dies.
I have read about setting the auto tune by idling for a few minutes then running at full throttle while dragging the chain down a log. I can't do that because it won't go to idle and goes full throttle with the trigger released.
Things I have chaced include removing the muffler and checking piston. It looks perfect. Removed carburetor and opened it up and cleaned it. It looked spotless and the diaphragm and gaskets are in good condition. Held 10 psi for over 5 minutes when checked from the end of the fuel line in the tank.
I checked compression and got 120psi on my gage that I know reads low.
I removed the clutch, oil pump and flywheel to get a look at the crank seals. I think I am looking at the bearing? Not like crank seals I have replaced or seen on other saws.
I have a vac/pressure tester but I don't have anything or anyway to block the intake.
Any ideas or directions on what I should check next?

Any help will be greatly appreciated.
TIA.

I have a 550xp Mk 2. When you start the saw DON'T blip the throttle after starting it. The saw has a high idle default when you come off choke and once you hit the throttle you set it to low idle. Let it warm up on HIGH idle for a few minutes first before hitting the throttle. If you last operated the saw in a very different temp/altitude the fueling may need some time to adjust.

 

[cscltd]

I think u have a leak at seals if you say u can see bearing.
pics of seals bearing would help

 

[edmxz2002]

I have a 550xp Mk 2. When you start the saw DON'T blip the throttle after starting it. The saw has a high idle default when you come off choke and once you hit the throttle you set it to low idle. Let it warm up on HIGH idle for a few minutes first before hitting the throttle. If you last operated the saw in a very different temp/altitude the fueling may need some time to adjust.

good saw welcome to the site.
look here for info:
Model Profile: 3700

I have a 550xp Mk 2. When you start the saw DON'T blip the throttle after starting it. The saw has a high idle default when you come off choke and once you hit the throttle you set it to low idle. Let it warm up on HIGH idle for a few minutes first before hitting the throttle. If you last operated the saw in a very different temp/altitude the fueling may need some time to adjust.

Thank you for your help. I don't know when or where this saw was last used. I got it from a local tree guy who was selling off some used saws to replace them with new ones. He said it was in the repair box and was probably put there because one of his guys reported problems with it. Overall it looks like it's in great condition I am hoping I can get it back up and running.
I will put it back together and try what you suggested tomorrow. I would still like to figure out how to block the intake so I can pressure and vac test it before running it too long.

Ed

 

[edmxz2002]

I think u have a leak at seals if you say u can see bearing.
pics of seals bearing would help

Pictures of the seals/ bearings? Are the seals built into the bearings?

 

[bwalker]

Pictures of the seals/ bearings? Are the seals built into the bearings?

Those seals appear to be fine, but a leak down test under pressure and vacuum will tell the story.

 

[HumBurner]

I have a 550xp Mk 2. When you start the saw DON'T blip the throttle after starting it. The saw has a high idle default when you come off choke and once you hit the throttle you set it to low idle. Let it warm up on HIGH idle for a few minutes first before hitting the throttle. If you last operated the saw in a very different temp/altitude the fueling may need some time to adjust.

Letting a cold saw race for "a few minutes" is counterintuitive to letting a saw warm up over "a few minutes"


I'm curious as to the thinking behind your comment.

 

[HumBurner]

Thank you for your help. I don't know when or where this saw was last used. I got it from a local tree guy who was selling off some used saws to replace them with new ones. He said it was in the repair box and was probably put there because one of his guys reported problems with it. Overall it looks like it's in great condition I am hoping I can get it back up and running.
I will put it back together and try what you suggested tomorrow. I would still like to figure out how to block the intake so I can pressure and vac test it before running it too long.

Ed

Many commercial tree folks are incredibly hard on their saws (or maybe it's just their groundies.) Buying something even they may be junking is beyond a crap shoot, regardless of how clean it looks.

Good clue for buying used saws, if possible, is look at the chain and bar on it. That generally tells you most of what you need to know before even touching the saw.

 

[edmxz2002]

Those seals appear to be fine, but a leak down test under pressure and vacuum will tell the story.

I'm going to try to get the intake blocked so I can do a leak test. I just need to figure out how I can block it.

 

[edmxz2002]

Letting a cold saw race for "a few minutes" is counterintuitive to letting a saw warm up over "a few minutes"


I'm curious as to the thinking behind your comment.

If I don't touch the throttle after starting, it doesn't race up. It only goes full throttle after I touch the throttle. Then it races up for 3 seconds and dies. I'm not sure running it even if it seems like it is not racing up is a good idea until I can confirm there are no air leaks.

 

[edmxz2002]

Many commercial tree folks are incredibly hard on their saws (or maybe it's just their groundies.) Buying something even they may be junking is beyond a crap shoot, regardless of how clean it looks.

Good clue for buying used saws, if possible, is look at the chain and bar on it. That generally tells you most of what you need to know before even touching the saw.

This didn't cost a fortune. I bought it to play with to see if I can repair it. I'm not in the repair business and I am not depending on this saw to make money. It's more of a "hey, I can probably fix that " kind of thing. If I can learn something along the way, better for me.
I appreciate the help and recommendations.

 

[Timber MacFallen]

Letting a cold saw race for "a few minutes" is counterintuitive to letting a saw warm up over "a few minutes"


I'm curious as to the thinking behind your comment.

You're curious to my thinking...Well, I own the saw and I have dealt with this issue previously.

High idle does not "race" the engine. It's an elevated idle. In fact high idle barely moves the chain. However, if the saw dies on contact with the throttle how do you expect the original poster to warm up at low idle? I'm advising he let the saw warm up on high idle because he cannot access low idle until he gets to temp most likely. Once he gets to temp he can switch to a low idle and let the computer do a base reset (which takes at least 3 minutes of low speed idling).

 

[oldbuzzard]

Read what Timber McFallen says about start procedure. On my Autotune and Mtronic saws I always let them run in high idle for at least a minute at first start of day. They then fine tune in the cut.
If you still have problems I would take it to a good Husky repair shop and have them run the diagnostics before I started tearing it apart.
Of course you should run a pressure check to be sure but theoretically Autotune and Mtronic saws compensate for air leaks. I’ve rebuilt a bunch of dead 550s off eBay and haven’t had a seal leak yet.
Otherwise your problem really sounds like Autotune issue. I’ve had one 550xp with the exact problem you mentioned and, before I knew better, I had mixed the coil/carb combination. That is to say that the software in the coil and carb has to match. A dealer has the diagnostics to check/correct that.

 

[bwalker]

I'm going to try to get the intake blocked so I can do a leak test. I just need to figure out how I can block it.

Make a plate out of metal plate and use a piece of inner tube as a gasket for the intake and exhaust.

 

[edmxz2002]

You're curious to my thinking...Well, I own the saw and I have dealt with this issue previously.

High idle does not "race" the engine. It's an elevated idle. In fact high idle barely moves the chain. However, if the saw dies on contact with the throttle how do you expect the original poster to warm up at low idle? I'm advising he let the saw warm up on high idle because he cannot access low idle until he gets to temp most likely. Once he gets to temp he can switch to a low idle and let the computer do a base reset (which takes at least 3 minutes of low speed idling).

I'm going to give this a try after I pressure test.

 

[edmxz2002]

Make a plate out of metal plate and use a piece of inner tube as a gasket for the intake and exhaust.

I will remove the intake and put the rubber between the intake and cylinder. I was trying to figure out how to block it from the carburetor end of the intake boot. It's got 3 ports and the impulse hole. I can block them all at once that way.

 

[edmxz2002]

Read what Timber McFallen says about start procedure. On my Autotune and Mtronic saws I always let them run in high idle for at least a minute at first start of day. They then fine tune in the cut.
If you still have problems I would take it to a good Husky repair shop and have them run the diagnostics before I started tearing it apart.
Of course you should run a pressure check to be sure but theoretically Autotune and Mtronic saws compensate for air leaks. I’ve rebuilt a bunch of dead 550s off eBay and haven’t had a seal leak yet.
Otherwise your problem really sounds like Autotune issue. I’ve had one 550xp with the exact problem you mentioned and, before I knew better, I had mixed the coil/carb combination. That is to say that the software in the coil and carb has to match. A dealer has the diagnostics to check/correct that.

The 2 dealers I called in my area don't have any one who can use the software for diagnostics on husqvarna saws. Do you know if I can ship the carburetor to a dealer for diagnostics, or would they need the saw with the carburetor attached?

 

[Squareground3691]

Check all ur fuel delivery lines and purge bulb , for leaks or sucking air , make sure there all tight ,

 

[Timber MacFallen]

I assume based on all the diagnostics mentioned in your original post you already did this, but I have to ask...Did you confirm the fuel filter is flowing properly and has no restrictions? If they are restricted they will mimic this problem. Lots of crap, debris and odd stuff can wind up in the gas tank of a service saw and they can get plugged up.

 

[edmxz2002]

I assume based on all the diagnostics mentioned in your original post you already did this, but I have to ask...Did you confirm the fuel filter is flowing properly and has no restrictions? If they are restricted they will mimic this problem. Lots of crap, debris and odd stuff can wind up in the gas tank of a service saw and they can get plugged up.

Yes, new fuel filter and all fuel lines have been tested for holes and fit tight on all connections.