Husqvarna 550xp Runaway Idle

[Golden Oldies]

I have a 550xp with about 25 hours of use. At times I've heard a rattling from the clutch side of the engine which has gotten louder. Recently, while cutting a log, I revved the saw up to finish a cut, and after releasing the throttle the revs would not come down. I stuck the bar into a block of wood and hit the kill switch. I restarted the saw, and as soon as I hit the throttle the saw idled up to max and stayed there. Today, we inspected the carb boot, and tested the clutch and mag side seals with ether and didn't observe any increase in RPM's. Spark plug looked normal, slight wear but good color. Muffler bolts were tight, and spark arrestor is clean. Could this issue be related to the "auto tune", this is the first saw I've had that has it? We weren't able to test the compression because of the tiny spark plug it uses.

 

[Squareground3691]

I have a 550xp with about 25 hours of use. At times I've heard a rattling from the clutch side of the engine which has gotten louder. Recently, while cutting a log, I revved the saw up to finish a cut, and after releasing the throttle the revs would not come down. I stuck the bar into a block of wood and hit the kill switch. I restarted the saw, and as soon as I hit the throttle the saw idled up to max and stayed there. Today, we inspected the carb boot, and tested the clutch and mag side seals with ether and didn't observe any increase in RPM's. Spark plug looked normal, slight wear but good color. Muffler bolts were tight, and spark arrestor is clean. Could this issue be related to the "auto tune", this is the first saw I've had that has it? We weren't able to test the compression because of the tiny spark plug it uses.

Possible air leak , seals , ext , can you do a pressure/vac test ,

 

[Wood Doctor]

Carb issue, no doubt. Unfortunately, these carbs are not cheap so just try this first: remove the carb and soak it for 24 hours submerged in mixed fuel inside a glass jar. Then install it once more and try again to see if the same problem prevails. It is rather surprising how many times this procedure has worked for me. If that fails, replace the carb.

 

[Golden Oldies]

Possible air leak , seals , ext , can you do a pressure/vac test

Thanks for the reply guys. I'm leaning towards a fuel issue as well. I'll disassemble the carb and either soak it or put it in the ultrasonic cleaner. I'm curious about the condition of the diaphragms, maybe causing it to run lean. I also might build an adapter and do a pressure and vacuum test with the Mighty Vac.

 

[Squareground3691]

Thanks for the reply guys. I'm leaning towards a fuel issue as well. I'll disassemble the carb and either soak it or put it in the ultrasonic cleaner. I'm curious about the condition of the diaphragms, maybe causing it to run lean. I also might build an adapter and do a pressure and vacuum test with the Mighty Vac.

Check all ur fuel delivery lines on saw to ,

 

[stihltech]

Do a vacuum and pressure test before buying parts.
From experience.

 

[Golden Oldies]

Here's an update guys. I made an adapter out of a spark plug to test for vacuum and pressure. I couldn't get it to build vacuum with the mityvac and realized that the air was getting in through the flywheel side crank seal. The seal and bearing have a weird plastic cover on it. Can this seal be replaced without splitting the case?

 

[mountainlake]

Make sure the bearing is good, seal shouldn't be out that soon but could be. Also spraying carb cleaner or WD at the seal will slow it down if there's a air leak Steve

 

[wilson225]

Check all ur fuel delivery lines on saw to ,

 

[Golden Oldies]

Thanks again guys. This seal is quite far gone. During my testing i noticed that it was bubbling slightly when sprayed with soapy water, but got worse as the testing continued. If the case has to be split I suppose i should do the bearings too as Steve suggested. I had hoped the seal would be removable from the outside and then driven into place around the crankshaft, but I'm concerned that the crankshaft will have to be removed. Any thoughts?

 

[Agrarian]

At times I've heard a rattling from the clutch side of the engine which has gotten louder.

This happened to my brother's 562 and I swore the sound was from the clutch side. However what I eventually found was that the crankshaft bearing on the flywheel side was bad and allowed enough play that the flywheel was smacking into the coil armature every time the magnet came around. Fortunately the bearing hadn't spun in the case so it was a matter of tearing it all down and replacing the crank bearings and seals.

 

[Tobystihl]

Plastic bearing race breaks up and rips out the seal.

 

[Wood Doctor]

One of my friends has a 550 XP that she loves and I will notify her of this thread. I have two Husky 350s and a 353 and have never observed any of these problems. These three saws have never had trouble like Golden Oldies reports here after close to 100 hours apiece of use. Amazing what you run into these days.


This 353 is my favorite, but I ran both 350's today and they both started and cut very well.

 

[Golden Oldies]

That 353 is a nice saw. I'm a fan of the 351 and 357. Just as an update, I've got the saw to the point where the case can be split, but I don't have the tools to do it. I've split older saws, where I didn't mind using a mallet, but because the saw is so new I'd like it done with the actual puller. I've asked the dealership to split the case and report back what they see inside. I told them to change both crank bearings and seals and press the case back together. I'll let everyone know what the report is!

 

[Golden Oldies]

Update: Problem Solved! In December I sent the saw to have the dealer split the case for me as I didn't have the press. They replaced the whole crank assembly with bearings and seals as the price was almost the same as the bearings and seals alone when labor was factored in. I rebuilt the rest of the saw and fired it up. The runaway idle was fixed, it must have been that bad seal on the mag side. I'd imagine the auto-tune was compensating for the seal leak for a while and then it got too bad. Thanks for all the help everyone.

 

[Pjohnson]

I've always owned stihl but I'd like a smaller 40cc saw like 540 or 543 but I keep seeing all these bearing and seal failures on husky. Kind of scares me off from husky. Stihl doesn't offer much in the 40 cc class pro saws, not sure what to look at.

 

[Golden Oldies]

I agree. In those smaller engine sizes it can be hard to find a saw that really performs well. Some of the huskys like the 240e seem to have decent seals but the carb and fuel delivery system is bad, so It's best to avoid those. Maybe something in the 50cc range would be best.

 

[HumBurner]

I've always owned stihl but I'd like a smaller 40cc saw like 540 or 543 but I keep seeing all these bearing and seal failures on husky. Kind of scares me off from husky. Stihl doesn't offer much in the 40 cc class pro saws, not sure what to look at.

543 is now discontinued, but available. Made in Japan and is a tweaked version of a Zenoah/Redmax designed saw.

Tough as nails, but.many people didn't like them. Run way too rich from the factory.