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576xp air leak?

Discussion in 'Chainsaw' started by Tinman204, Apr 14, 2019.

  1. Tinman204

    Tinman204 ArboristSite Operative

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    I'd like to pick some of your brains on my new saw.. Ill try and make this brief.

    I picked up a 576xp non at off my buddy a week ago, saw has a new meteor piston and carb kit. It was built from several saws.

    Saw ran great first tank, we cut a bunch of small 12" wood with it when I picked it up.

    Went cutting yesterday and it ran great for the first 10 mins, then after cutting some big wood it seems to not want to go back to idle, seems a bit lean to me. After cutting it slows down to almost idle but often the chain keeps moving, fattening up the bottom fixes it till I cut again and then it goes right back to lean.

    I tuned the saw in the wood it 4 strokes nice out of the cut and is slightly fat while cutting, perfect for break in.

    Plug is golden brown, everything looks fine.

    Saw failed a vac test and passed a pressure test this morning.. Check it with soapy water and couldnt find any leaks.

    Checked the cylinder and case bolts, they were tight. I resealed the oil pump bolts and also checked the impulse line and intake.

    Everything checks out fine on the saw, but it seems a bit lean only after I get it warm and cut big wood with it.

    Question is where would you guys look for problems?

    Crank seals is my thought.

    Any help would be great..
     
  2. Duce

    Duce Addicted to ArboristSite

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    Those saws are known for spinning clutch side bearing in case. I would pull clutch and oil pump to check that. Did he use sleeve locker to set that bearing when it was rebuilt? Saw should pass vacuum check.
     
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  3. Tinman204

    Tinman204 ArboristSite Operative

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    I already pulled the clutch and the oil pump and the bearing appears to be fine.

    The bottom end wasn't touched yet to my knowledge.

    Guy who built the saw has been wrenching on them for 30 years or so. I could bring it back to him but thats no fun.
     
  4. Duce

    Duce Addicted to ArboristSite

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    Did you crank it over to see if bearing spun in pocket? Mark bearing position and crank it over fast.
     
  5. Tinman204

    Tinman204 ArboristSite Operative

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    Yes, i did that while pressure testing to try and make it leak.
     
  6. Duce

    Duce Addicted to ArboristSite

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    That bearing is a sealed one $36, check flywheel side seal.
     
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  7. Tinman204

    Tinman204 ArboristSite Operative

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    Couldn't make either flywheel or pto bubble under pressure.

    Thanks for your help duce, guess I'm on the right track, ill order new crank seals this week and install them and go from there.

    Flywheel seal looks ok but that doesn't mean much.
     
  8. Ronie

    Ronie ArboristSite Operative

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    You can spray a little WD 40 on the seals, apply vacuum and see if it sucks it in.
     
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  9. Tinman204

    Tinman204 ArboristSite Operative

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    Thanks for the wd 40 trick. That seems like a good way to see if its a seal failing under vac.

    Just pulled the pto side seal as I realised I had a new seal in my spare parts here. Old seal seems a bit hard and brittle compared to the new one. I installed the new seal so thats 1/2 the job done..

    I'll grab a flywheel side bearing this week.
     
  10. huskihl

    huskihl Addicted to ArboristSite

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    Usually when they pass for pressure and fail vacuum, it's sucking the decomp in
     
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  11. Tinman204

    Tinman204 ArboristSite Operative

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    Thanks for the info.

    This saw has a decomp plug installed so unfortunatley I cant get off so easy. :)
     
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  12. Sam R

    Sam R 8mm Socket

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    I always take out decomps when I do p/v testing since they will leak a bit - and that's normal. But if that was your leak then it doesn't explain your poor running.
    You said the carb was rebuilt, were the checks tested for proper operation? If it's wanting to run out or not idle properly you might have a bad high speed check. Especially if it's running well at WOT.
     
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  13. Tinman204

    Tinman204 ArboristSite Operative

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    Well to be honest I'm not suspecting the carb at this point. (I could be wrong)

    My buddy built 3 576s in a row. The carb that is on my saw was previously installed on his personal 576xp. His saw ran perfect with this carb.

    He ended up getting an autotune parts saw and put the autotune on his saw and used the carb to complete my saw.
     
  14. Sam R

    Sam R 8mm Socket

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    Oh okay, if it was running fine just that recently it's probably fine. Pretty much your other culprit is your seals/intake boot or impulse line, most likely. You could try bypassing the deco entirely and run it with just a bolt & crush washer in there and see if that clears it up. Then it's your deco valve. Not unheard of for them to go bad.
    Usually bad seals will fail your vac test, though.
     
  15. Tinman204

    Tinman204 ArboristSite Operative

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    Ive been running this saw with no decomp since I've had it..

    I'm still going to go with crank seals at this point. Hopefully if I have time today I'll stop by my husky dealer and grab seals along with a couple other parts I need.
     
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  16. Tinman204

    Tinman204 ArboristSite Operative

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    So had to order a crank seal from the dealer today, it will be in stock in a week.

    In the meantime I think I'm going to pull the intake and give it a good inspection and reinstall it with some yamabond to make sure it is sealed.

    Maybe I'll do another vac test tonight and apply some heat to the flywheel side seal and see if I can get it to leak under pressure.

    got this saw for a friend price so no matter what is wrong I'm ahead for sure.

    I actually wanted to buy it in pieces but my buddy wanted to finnish the project.so at least i get to do some wrenching on her and get to know her a bit before we get to cut lots of wood. :)
     
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  17. Sam R

    Sam R 8mm Socket

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    I love a good project, helps to be able to suss out the problems though. I always rely on AS members when I get stumped. Haven't led me astray yet.
     
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  18. Tinman204

    Tinman204 ArboristSite Operative

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    Was messing around in the shop checking things over on the saw. Pulled the intake, impulse line and rechecked every bolt. Found nothing.

    I installed rubber behind the intake and did another vac test. Found nothing.

    Then removed the rubber and reinstalled the intake and carb this time putting rubber behind the carb instead of plugging the intake like i did the first time.

    Did a pressure test and could hear a leak at the carb flange. No matter what I did it would leak.

    And then it hit me like a sack of bricks.

    The support sleeve that fits inside of the intake where the carb bolts up isnt there.

    That could make an air leak I recon?
     
  19. Tinman204

    Tinman204 ArboristSite Operative

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    Just another update for anyone interested.

    I put a support sleeve in the saw and fired it up. It ran fine like normal for a couple mins then crappy again.

    I removed the clutch and oil pump sleeve and left the top cover off.

    I let it idle on the bench and sprayed starting fluid around the crank seals, base gasket and case halfs.. Saw ran fine no change in idle.

    Next sprayed the intake where it mounts to the cylinder, again nothing..

    So I gave a little shot at the left side of the carb mounting flange...... nothing!

    Was starting to wonder if maybe i do have a carb issue.

    Then I decided to spray the right side of the carb flange, the saw stumbled instantly and died!!!

    It seems the intake is a bit stiff and or the mounting flange is a bit warped meaning it wont seal.

    I think I'm going to order a new intake, support sleeve, mounting flange and screws.

    So glad I found my leak. It was starting to drive me nuts but with some paitience I found it.
     
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