576xp won't start, bad coil?

[mbrick]

Saw won't run, and I think it may need a new coil. I have not experienced a dead coil before to understand symptoms. I know, air / fuel / spark.

I bought it not running. I put in a new spark plug when I got it and ran it for a few minutes before taking it apart — plug that came in it was missing the aluminum nut. I idled and rev'd it a few times but did not hold it WOT.

I finished reassembly (separate thread), changed one crank seal to fix a leak, verified it passes a vacuum test of 15 inHg for 15 min, didn't move at all. New Zama rebuild kit for the carb.

It fired up but seemed a tad rough. I haven't owned a saw this large for reference though. I let it idle for several minutes while adjusting the L screw. I held it WOT and it ran for a few seconds then it just shut off. Would not restart and won't start now.

I am fairly sure it is getting fuel, it is wet in the cylinder. I sprayed some premix in the spark plug hole and it still didn't start. Disassembled the carb twice and looked it over, all passages appear clear and it holds pressure. Compression is still 140psi.

It is sparking but it looks weak to me. I changed the new BPMR7A OE plug for a non-resistor plug and it fired up and blew a TON of smoke and oil. Wouldn't quite idle though. I put the BPMR7A back in and it will not start. It seems like it is trying (can feel it a bit on the cord) but it just won't start. Weak with a resistor plug makes me think the coil is bad?

I do not have another saw I can borrow a coil from, only have AT saws.

Here is a shaky video of the spark, best I can do while pulling the recoil over:

 

[Tenderfoot]

Is your gap set right? you said you did crank seals so I assume the flywheel came off at some point. It may have too much or too little gap between the coil and the flywheel.

 

[mbrick]

Is your gap set right? you said you did crank seals so I assume the flywheel came off at some point. It may have too much or too little gap between the coil and the flywheel.

Yes the flywheel and coil were removed, I completely stripped it down.

I followed the service manual for the gap at 0.3mm. Just double checked and it is 0.38mm at the middle and 0.50mm at the bottom, doh. I can't get them both to be the same because the arc on the coil laminations is larger than the diameter of the flywheel if that makes sense, so the gap at the top and bottom will be more than the center. Also the flywheel has a bit of runout so it is tough to shim on the non magnetic side and get the correct value on the magnet side.

I will readjust it now and try to get the middle at 0.30mm.

 

[mbrick]

Ok, I adjusted it to 0.3mm at the bottom and just under 0.3mm in the middle. It will start with the NGK BPMR7A but runs pretty crappy.

I had to turn the idle up quite a bit, and it still hiccups a bit at 2700rpm. I went back and forth with the low speed and sometimes it suddenly dies. Doesn't seem to rev very smoothly.
I am at stock screw settings at 1 1/4T low and 2 1/2T high.

It also won't start with the decompression on. It seems like it won't fire strong enough to close it. If I pull it closed it will start.

 

[mbrick]

Coil resistance is 85 ohm primary 1500 ohm secondary. It's within an order of magnitude but not the same as what is listed in post #2 here:
https://www.arboristsite.com/commun...-resistance-measurements.180482/#post-3152852

The trailing magnet passes the middle of the coil at TDC so as a rough gauge it seems ok. I also reinstalled the flywheel and the molded-in key was still there.

The saw was sold as not running so other than the plug that may have just been stuck in for shipping, and the loose cylinder bolts, there should be an issue somewhere so maybe it is the coil?

 

[mbrick]

My saw has coil 510 11 57-03 (blue). I can't find this part number in any google search or IPL which is weird. It says 2010 on it and my saw is a 2011.

2010 IPL 510 11 57-01 (blue) $42
2011 IPL 522 79 54-02 - no results
2013 fiche 510 11 58-02 (gray) $51. Might be autotune only.
2017 IPL 522 79 54-02 - no results

For $42 if anyone else thinks this sounds like a coil I'll order a new one.

 

[Brent Nowell]

Spark,proper fuel/air mixture and compression is what’s needed to start an engine. I always go back to the basics and go from there.
It seems we know we have spark, so goto fuel/air mixture.
Check the carb/boot/air horn mounting screws, make sure they are tight. I have seen these loosen up over time causing small air leaks which cause issues like you describe.
Your set screws for fuel are correct, or at least close enough to get the saw to run properly.
Make sure cylinder head bolts are tight.

Now compression,
Check your decomp valve, make sure it isn’t leaking when you pull the starter cable slowly. I’ve seen these leak and cause missing when the saw is running.

Pull the exhaust and make sure the piston looks ok, again part of the compression factor.

If those are not it, we need to examine more complicated issues in the fuel/air catagory. Probably a cracked boot, or carb needs a rebuild. Leak down test will need to be done at this point too

Process of elimination and we will get it.

 

[Tenderfoot]

I would look for air leaks and loose fuel lines before throwing a coil at it. It sounds like you are on the right track.

 

[mbrick]

Brent, I just tore it down for a rebuild so I saw the pistons and ring. Compression is still 140 after about 8 pulls when it peaks.

I also vacuum tested after reassembly and it passes 15 inHg for 15 min (doesn't drop at all). Decomp valve sealed even when I twisted it.

I used block off plates where the carb goes so I know the intake boot to cylinder is good. All bolts still tight on intake and cylinder.

Should I remove the exhaust and carb and leak test it again?

New fuel line and filter. Carb is definitely getting fuel, each time I open it it is full of fuel on the pump and jet side. I blew carb cleaner through it and the pilot and mains are clear from what I can tell.
I could put the old carb parts back in?

 

[Brent Nowell]

Brent, I just tore it down for a rebuild so I saw the pistons and ring. Compression is still 140 after about 8 pulls when it peaks.

I also vacuum tested after reassembly and it passes 15 inHg for 15 min (doesn't drop at all). Decomp valve sealed even when I twisted it.

I used block off plates where the carb goes so I know the intake boot to cylinder is good. All bolts still tight on intake and cylinder.

Should I remove the exhaust and carb and leak test it again?

New fuel line and filter. Carb is definitely getting fuel, each time I open it it is full of fuel on the pump and jet side. I blew carb cleaner through it and the pilot and mains are clear from what I can tell.
I could put the old carb parts back in?

Well it’s most likely not an air leak. You should however do a test of vacuum and pressure on the hoses. If this saw has an impulse line for pumping fuel to the carb, test that too. If it does not make sure that the the hole is not blocked on the intake manifold and that it is sealed properly to the face of the carb.
If that is not working it is possible and likely that you are getting an improper fuel amount from the carb, due to a stiff diaphragm or needle/spring issue. This is not really my area for rebuilding testing carbs so I cannot give you specifics. I can say however that the diaphragm must not be stiff at all and should be extremely pliable with no tears or cracks.
Good luck my friend

 

[mbrick]

I did the vacuum test through the impulse line with the spark plug and carb blocked, and I think the carb nipple is mating with it correctly (I can see it when installing the carb).
The new diaphragm was very soft and pliable. I can try putting all of the old parts back in the carb to see if that makes a difference.

When I removed the carb the first time I did double check the impulse line was not blocked by blowing air through it.

 

[Sam R]

Do you have another BPMR7A you can use? A bad plug can do you like that, too.
Have you done any testing of the carb outside of the rebuild? Pressure testing the inlet, check for side-to-side play in the throttle shaft. Check the hi speed circuit for proper sealing.

 

[Brent Nowell]

Holy moly.. alright heh this one seems to be a doozy.. ok
Just to be clear at this point the saw does run but runs poorly?
Describe how it runs in the best detail you can, better yet post a video.
Is the plug fouling when the saw dies?

 

[mbrick]

It does run at this time, but poorly. I don't think the plug is fouling, it looks ok to me and is not oil soaked or anything. I went and got fresh gas today to rule that out, no change.

Ok, took a bit to provide an update as I did a few things:
1. Leak tested again from exhaust to carb boot through impulse hose. Still pass 18 inHg vacuum with no drop while rotating crank.
2. Compression 140psi.
3. Reinstalled all old parts in the carb (pump side, needle, lever, diaphragm, spring)
4. Tested tank vent, and it seems to meet the 150mbar vent and 115mbar vacuum spec. It is not plugged and is venting.
5. Put in a non resistor Bosch spark plug I had. 0.5ohm from electrode to lug.

It runs only with the Bosch plug, so maybe the NGK is bad. I can see by eye a brighter spark with the Bosch.
It will not start with decompression on and pop the decomp closed as expected. The decompression has a nice click in/out and is not sticky either.

The carb shaft is not worn. Everything in the carb looks clean and the screen was clean when I first opened it. I can spray carb cleaner through the main jet passage and the pilot comes out of the three holes in the bore.

Here is a video in the current state. I have the idle turned far in about 2 turns from where I can see a wear mark on the screw. At first in the video I start it with the decomp on and you can hear it run but as soon as I touch the throttle it died. I tried adjusting H from about 1.5-3.5 turns and it still peaks around 10.8k rpm and sounds crappy. The blue coil is 13300 limited (says on the side). After running in the video the cylinder is 200F and front of the exhaust 400F.

 

[Brent Nowell]

To me that totally sounds like an air leak or fuel delivery issue. I know you have vacuumed and pressure tested the case from the exhaust to the boot. Have you examined the boot carefully? The 576 I believe has three separate air channels made of rubber. Examine the rubber carefully , there has to be a crack of some sort on it, it’s the only place left. Bend it in all areas to try and find it

*edit I see you did check the decomp

 

[Brent Nowell]

Also did you try pressure instead of vacuum? 18hg is plenty good btw I had to look it up cause I was not familiar to it. Thought it was similar to inches of water column which would be way too little, but it works out to like 8psi

 

[TRTermite]

Also did you try pressure instead of vacuum? 18hg is plenty good btw I had to look it up cause I was not familiar to it. Thought it was similar to inches of water column which would be way too little, but it works out to like 8psi

HG stands for mercury... inches of HG is measuring how High a vacuum will pull a given amount of HG in a given area (Laymen terms) Psi is pound per square inch as Pressure so one is sucking and one is blowing Can't help you with your problem but reading your posts hoping it will help me with mine..

 

[Plan-b]

It looks like a fuel issue, go threw the carb again or try another one. Remember that a saw with an air leak will respond to the mixture screws being turned. (It may not be consistent, but it does respond) This one is not.

 

[mbrick]

Ok, I tore it down again and pressure tested it to 8psi and vacuum to 15 inHg again. While under vacuum and pressure I squeezed and poked at the intake boot and pulse line. Yes it has three air channels. No leaks anywhere. I thought maybe the pulse line wasn't getting a good seal on the carb nipple so I put some leak detector solution and cranked it over and no leaks.

I took the carb apart again and looked everything over carefully. I also left the diaphragm side off, and cranked over the engine while holding down the lever. It pumps a LOT of fuel and jets out around the needle.

It runs kind of crappy right now but starts consistently.
If I stab it and give it full throttle it will bog and die. If I give it partial then full it will rev up. Will not start and run using the decomp. It does not seem to respond well (almost none) to the mixture screws.

With the air filter off, it sprays back some fuel when I grab the throttle. It is definitely getting fuel?

I bought a new carb and will try it when it arrives. I don't know what the issue is with this one.

 

[Old2stroke]

If there is a lot of spray back from the carb, that is suspicious. Is there a chance the saw had a bad porting job done before getting rid of it? Maybe the wrong piston installed?