576xp won't start, bad coil?

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Did you ever squirt a little fuel into the spark plug hole and fire it up? If it pops right off and sounds healthy it might provide a clue to your “situation”.
I did try dripping some premix in at first when it at first was not running. It didn't help. Which made me initially think it was the coil...

Derrick that is a good question, I think it is an illusion and it is not running backwards. I also just confirmed the starter is pulling it over in the correct direction (counter clockwise when looking at the flywheel).

Here is a video of the piston fit skirt first and crown first. It seems loose, does it seem like enough to keep it from running? $80+shipping for a piston kit.

 
While it does seem loose, i am not sure if that would cause the symptoms you see. Though it could prob use a new piston/rings, i think i would first get a cheap unlimited black coil since they are helpful to tune the saw anyway due to the cutoff of the blue coil. If there was an air leak or a too little fuel i would expect rpm to surge not be limited to ~10K. I wonder if anyone has an extra to sell or lend you that they know works, like from a 372xp.
 
Mystery continues. The ring end gap is definitely a bit big, nominal gap should be .004" per 1" of piston diameter, so .008" for your saw. Piston doesn't sound too bad so that large end gap could be what is causing the spray back through the carb but I don't believe this could be the main cause of how the engine is running. When you installed the new carb, did it respond at all to the setting of the "L" screw? By process of elimination, it looks like trying a new coil is the best move. These coils are really an ignition module with semiconductors and a simple resistance test of the terminals in not conclusive to how good the coil is. As this is a strato engine, it would be great if someone with experience would join in as there might be some issue with the timing of the strato throttle opening relative to the main carb throttle.
 
Ok, I will order a piston kit and coil. It could probably use rings anyway, so I am just going to get a piston kit since the piston is also visibly worn.

I was going to order the blue/limited 510115701 coil listed on the fiche because I know it will fit. I'm not sure which unlimited coil would have the correct length wire, and on the 372xp fiche I see 510115701 which is also blue/limited.

The new carb barely responds to L, it takes several turns, I think it is responding to almost full closed when it dies and 2-3 turns out. It seemed the same as the old carb. I don't have a gauge as to how sensitive it should be.
 
Mystery continues. The ring end gap is definitely a bit big, nominal gap should be .004" per 1" of piston diameter, so .008" for your saw. Piston doesn't sound too bad so that large end gap could be what is causing the spray back through the carb but I don't believe this could be the main cause of how the engine is running. When you installed the new carb, did it respond at all to the setting of the "L" screw? By process of elimination, it looks like trying a new coil is the best move. These coils are really an ignition module with semiconductors and a simple resistance test of the terminals in not conclusive to how good the coil is. As this is a strato engine, it would be great if someone with experience would join in as there might be some issue with the timing of the strato throttle opening relative to the main carb throttle.
Good point, particularly about the coil test. I don’t think the coil test will show if say the timing advanced portion of the coil is working properly. I’m pretty sure this is micro processor controlled to some degree, it has to be if the timing is changing during rpm transitions.
Check this thread particularly post #16
https://www.arboristsite.com/community/threads/ignition-coil-spark-advance.265075/
 
Brent, that thread has a few useful data points and bad coils. I may try a timing light on this coil once I get a new piston in.

I ordered a new OEM piston kit, wrist pin bearing, coil and coil boot. I will check back in when they arrive in a week or so.
 
Just a word of caution from the video. It's risky to run a saw for any length of time without the top cover on. The cover has to be there to properly concentrate the cooling air from the flywheel through the cylinder fins or the saw will quickly overheat. NEVER run the saw under load without the top cover on, shocking how fast the saw will overheat and self destruct.
 
Brick I find it very odd why it doesn’t respond to the low jet... idle screw should just touch throttle cam, the. Open so it’s just cracked. Reset L jet to 1.25 turns out. Sorry if that sounds dumb just throwing ideas out
 
I cant help much on this thread.

I will say though Ive been dealing with a 576xp that is leaning out after a cut. I found a leak at the carb.

My carb L screw can be turned right in before the saw dies and on the high end even with a major leak at the carb my L screw is only 1.5 to 2 turns max.

Any more then 2 turns and its smoky and loads up idling..

2 to 3 turns out on the L screw seems like too much to me.
 
He already tried to new carb though. My 576 accelerates fine with L screw out to 3 turns without any smoke but its set around 2 turns out now (1/4 out from max rpm at idle). the H side was tougher to adjust but also around 3 turns out. I had to swap in a 372xpw coil to make it easier to tune. It four-strokes fine and cuts/idles well but the plug is a little more light/yellowish than i prefer. I tried a new plug and it was the same. I
 
New parts arrived. Still runs like crap. Gah.

New OEM piston/rings 575 25 73-04, wrist pin bearing, coil 510 11 57-01.
Leak test passed under vacuum after re-assembly. I also left the spark arrester screen out even though it looks clear.

I was running it with the cover on and even after a minute or so messing with it, the cylinder is too hot to touch by hand. Idle needs to be turned almost all the way in and it pops/sputters/backfires when holding it WOT. I didn't want to hold it open for too long because it seems hotter than normal and is immediately obvious something isn't right.

I think tomorrow I will try 3 turns out on both screws just to rule out that it is lean based on what Derrick said.

For those curious, here are measurements with the new parts:
New OEM Piston (Mahle, Made in Germany):
50.72mm top
50.83mm below rings
50.93mm bottom
50.86mm on the sides
11.994mm wrist pin diameter
Ring gap: .013" at the base and above exhaust port
Compression immediately after assembly: 143 psi
New coil: 89hm kill switch side, 1600 ohm primary at boot

Old piston (identical part compared to the new one so it wasn't a 575 piston):
50.66mm top
50.79mm below rings
50.86mm bottom
50.82mm on the sides
11.991mm wrist pin diameter
Ring gap: .017" top ring, .013" bottom ring
Compression: 140 psi
Old coil: 85hm kill switch side, 1500 ohm primary at boot



IMG_20190506_174025.jpg IMG_20190506_171054.jpg IMG_20190506_172352.jpg
 
Yikes, how frustrating, there was another 576xp post where the metering lever in the carb was not at the correct height, even a new one, I wonder if its flooding the saw.....the choke plate isn't sticking or anything? These could explain low max rpm too
 
I did check the metering lever height in both carbs. A hair below flush with the body. It was correct in the new carb but pretty far off with the genuine rebuild kit parts I was first using.

I don't have enough experience tuning to know if it is too rich or too lean.
 
Yikes, how frustrating, there was another 576xp post where the metering lever in the carb was not at the correct height, even a new one, I wonder if its flooding the saw.....the choke plate isn't sticking or anything? These could explain low max rpm too

That was my saw. Darn thing gave me some gray hair.. i checked and rechecked everything, saw ran like crap.

My metering lever is flush with the base now, with it slightly low my saw ran like crap.

That was a brand new zama carb with maybe 5 hours on it max..

I was actually shocked at how a few thou on the meter lever height had such an impact on how the saw runs.
 
The only thing he hasn’t replaced is the coil!!!! Lmao what a doozy,

Are you going to try replacing the coil?
 
If a new coil doesnt fix that saw then its cursed!!!
I already did replace the coil in post #21, with a new OEM coil. I first ran it with the new piston and old coil, and then put in the new coil. It ran exactly the same with both coils.

As a side note, it was a PITA to put the spring terminal and boot onto the coil wire but I finally got it by pushing the wire through the boot, putting the spring on, and then pulling it back into the boot.
 
How well is that coil grounded? Makes you wonder if maybe the posts or the ground wire washer is dirty and or loose
 
I think your problem lies in the cylinder.those transfer lines don't look to good.did ya happen to try and clean the cylinder up before putting in the new piston?if not the rings probably won't seat good.kind of bad thing ya spent 80 some bucks on a OEM piston.ya could have had a hole new top end for 167.00 I doubt your problem is with spark with a new oem coil and what you have done.i know it sucks becomes a money pit.[emoji16]

Sent from my Pixel 2 XL using Tapatalk
 
I already did replace the coil in post #21, with a new OEM coil. I first ran it with the new piston and old coil, and then put in the new coil. It ran exactly the same with both coils.

As a side note, it was a PITA to put the spring terminal and boot onto the coil wire but I finally got it by pushing the wire through the boot, putting the spring on, and then pulling it back into the boot.

Jeez man, and I thought my 576 was a PITA!

So you've changed the carb, piston, coil and it passes vac and pressure test and it still doesnt run???

Hmmmmmm, cylinder maybe???
 

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