576xp won't start, bad coil?

[brad ruch]

Key signs
Saw is running hot and won't start with the decomp on.its cause to (low compression)

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[Tinman204]

I went back and read this whole thread again.

As above im going with a new cylinder is needed.

That old piston seems way too loose for that cylinder to still be good.

I could see honing marks in the bore in the picture so perhapse someone honed that cylinder a bit too much and its now out of spec causing low compression and pour running.

 

[mbrick]

Saw is running hot and won't start with the decomp on.its cause to (low compression)

Ok, I'm listening. Why would low compression cause the saw to run hot? It does show 140+psi, I would have expected it to read lower.

Also, isn't the cylinder plating very thin so I would be able to see through it if it was worn? Yes I also still see honing marks.

What do you mean by transfer lines? Yes I cleaned it up with scotch brite, no honing though.

I'm not opposed to ordering a piston/cyl kit, just want to understand it is the correct next step because I don't have a lot of experience with saws and knowing what problems a new top end fixes. I would hate to bolt that on and still be in the same place I am now.

I don't think the new piston was a waste, I can still use it in the new cylinder.

 

[brad ruch]

Top end from Husqvarna is 167.00
https://www.ahupd.com/search.asp?keyword=575257406
I could see the lines down the intake and exhaust side in the cylinder.if that won't clean up.then it's in the plating and that will cause some loss in compression.and low compression the saw won't get the heat out like it should.i just did a 394xp with this similar thing happen.i had the cylinder cleaned up good with new piston and rings.compression seemed good.but ran not to great and lower on power.got hit enough to melt the paint on the muffler.put a new cylinder and piston in it and problem solved.

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[brad ruch]

The cylinder kit comes with a new piston also.so I guess you could just sell one piston.[emoji6]

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[brad ruch]

Here is for the metering lever arm also.

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[mbrick]

Ok, I ordered the OEM top end kit. $150 via Amazon Prime. Will update once I get it installed.

As brad mentioned I will keep that piston as new and use the current 'new' one that has about 3 minutes of run time on it unless you think the rings will not break in to the new cylinder.

Thanks for the metering lever, that matches what I found in the service manual. It's currently set at just under a hair below flush.

 

[mbrick]

I put on the new top end. Passes vacuum and pressure test. It seems to run smoother. Still a little laggy off idle.

It is still topping out at about 10.5k rpm with 3T out on the high screw. This is with no bar and chain.
I adjust low speed and when turning in reading the tach for peak rpm. It peaks at about 1/2T and then stays constant until the screw is all the way in. So I went back to where it first peaks, then out 3/4T per the manual.

It will still not start with decompression on. It "runs" with the button still down then dies if I touch the throttle. I cleaned the button when I moved it to the new cyl and it actuates well and has a nice click to it.

Using pre mixed 40:1 in a can to rule out all variables. It is still pretty oily around the exhaust so I am going to remove the carb and move the metering lever down a tad and try that per some earlier comments that even at flush it does not run well.

The ring gap for new OEM P&C 575257406 was .011" at the base.
Now that it's been run in a few minutes I will check the compression when cold.

Maybe I need to try cutting with it?

The "new" piston I ran in the old cylinder looks like it was already getting beat up per the shiny area on the exhaust side (photo below). So I'm glad to go with a new top end.

 

[brad ruch]

I would check that metering arm.thats running very rich.which is the cause from all the oil,gas mix around the exhaust.10,500 is way to rich.

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[brad ruch]

New cylinder should have come with a decomp plug.just plug the decomp for now.I usually don't use them unless your doing a base gasket delete and increasing compression then yeh.

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[mbrick]

New cylinder should have come with a decomp plug.just plug the decomp for now.I usually don't use them unless your doing a base gasket delete and increasing compression then yeh.

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It did come with a plug yes. I kept the base gasket and added a thin layer of 1211 on each side, the machining marks on the bottom of the new cylinder were a bit coarse.
I moved the decomp over because I use it on my 550xp and it works well. I can just ignore it for now. I was not sure if the larger saws generally just don't work well with them?

Ok I'll check on the metering arm. It is flush so I will bend it down a tad. Glad you confirm it is rich, I was not 100% sure.

I am out of town the next few days but will update when I am back and get to adjust it.

 

[Tinman204]

If the saw is running good enough to cut I say run it and see what it does.

It does look super rich from the pictures, it seems these zama carbs are very sensitive to metering lever adjustments.

Mine sure was. Literally a couple thou on the lever height made my 576 go from leaning out after a cut to running nice and rich. I've never had a carb so picky and my carb was a brand new from zama, never been opened.

 

[mbrick]

I was on vacation and then away for work but spent some more time with the saw today.

I lowered the metering lever to the negative side of the spec at 0.3mm below the carb surface based on feedback that it could be too rich.

It runs about the same. Not well. Sluggish to rev up, and still sputters around 10k rpm.
Idle screw all the way in past the taper and it idles most of the time, but not well. I can see a wear mark where it was at one point and it's only about 1/3 up the taper on the end of the screw. It also still seems to run a bit hotter than I expect.

If I hold it WOT and turn the H screw all the way in and then out to 3T, it starts out barely revving up, then gets a little better, then gets sputtery at 3T. It is never screaming at 13k rpm.

Same result between the original rebuilt carb and new carb. I also checked the hi speed jet check valve in the original carb and it is present and functions by holding vacuum.

I just compared it side by side to my 550 and this revs up instantly right to the ignition limit. Let off and it drops right back to idle. After WOT for a bit it seems cooler in comparison.

I'm not sure if I just really don't know how to tune it or if there is something wrong?

I'm close to throwing in the towel.

 

[Tinman204]

Dont feel bad, my own problem 576xp has also been a 4 month saga.

Thought I had my issues beat until a couple weeks ago when the saw started running like crap again.

I through it under the bench and am taking a break. Im tired of throwing parts at it and i suspect the problem is with the brand new carb thats on it.

 

[mbrick]

It does seem like it is the carburetor but I don't know how I could have two duds.
Are you using the Zama C1M-EL28 or C1M-EL50? I don't know what the real differences are based on the ending digits.

I wonder if the autotune carb is better? I see it listed as Zama C1M-EL40C.

The autotune carbs on my 550xp and 555 are both absolutely perfect. The 550xp is a Walbro, and the 555 is a Zama C1M-EL46.

 

[Tinman204]

I'd have to check but C1M-EL28 rings a bell.

My plan is to probably make my saw auto tune as my buddy has all the parts. I'm 99% sure its my carb..

My saw runs completely different then yours though so im not sure if we have the same problems.

 

[mbrick]

I'd have to check but C1M-EL28 rings a bell.

My plan is to probably make my saw auto tune as my buddy has all the parts. I'm 99% sure its my carb..

My saw runs completely different then yours though so im not sure if we have the same problems.

I'm interested in your result if you convert. Does it only require the stator, autotune generator, and carb?

I can't decided if I should convert it to autotune or buy another saw to use for troubleshooting parts. But that would really be diving in.

 

[Tinman204]

I'm interested in your result if you convert. Does it only require the stator, autotune generator, and carb?

I can't decided if I should convert it to autotune or buy another saw to use for troubleshooting parts. But that would really be diving in.

Yep thats all it takes and it becomes an auto tune.

My biggest issue is my saw was AT and the generator screws came loose and they broke off. So i cant just bolt a generator to my cases.

So if i want to go AT I have to swap cases. Really its a couple hour job and at that point I can install new bearings and seals.

Id really like to be cutting firewood with my 576 vs constantly working on it.

 

[Numb arms]

Hi Mbrick I am a couple of years too late it just read your saga obviously having issues with my 576xp as well won't fire. Anyway from what I read the idle screw was unresponsive and the saw would max out at 10 . For the idle screw to be unresponsive too much fuel or too much air or turbulent flow of both. Did you ever replace the intake boot.?

 

[mbrick]

Hi Numb arms... after many part swapping and time spent on it the issue ended up being related to timing. The flywheel spun and the timing was from what I estimate 45 degrees or so advanced.

The flywheel must not have been tight enough and then spun when I was pull starting it. The integrated key sheared (soft aluminum), but once I realigned it fairly close to the original position it fired right up.