Stihl Magnum 038 will not start

[fobicboy]

I own a Stihl Magnum 038 saw that has recently stopped and will not start. I checked for spark and I am getting one, I went ahead and replaced the spark plug to insure that it is not defective. I removed the air filter to confirm the at the saw is getting air. I bypassed a fuel flow check by simply spraying ether into the spark plug hole. When I attempt to start the saw I get nothing, not even a back fire or pop. I sprayed ether into the carb throat and had the same result.

Since I know I am getting spark this behavior is baffling, the saw should at least backfire or pop when the ether is introduced. I do not have the service manual so I am ignorant of the ignition system, no idea if there is a timing problem. I checked for spark in two ways, first I grounded the spark plug again the block and I saw it fire, then I connected a tool in series with the spark plug that lights a neon bulb when spark is present. Both tests show spark.

Does anyone have an idea what might be going on here?

 

[Justin Taylor]

You could take the flywheel off and see if you have a broken key if you thing it’s timing but do u have compression?

 

[merc_man]

Pull muffler and look for scoring.

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[merc_man]

And dont use ether. Its hard on stuff.
My 2 cents

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[KMSwr]

And dont use ether. Its hard on stuff.
My 2 cents

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Carb cleaner is safer.

 

[fobicboy]

Thanks for the input, Hmm fly wheel key & compression...that should be easy to check.

Does anyone know if the flywheel nut is reverse thread? That is clockwise to remove?

 

[Mad Professor]

Thanks for the input, Hmm fly wheel key & compression...that should be easy to check.

Does anyone know if the flywheel nut is reverse thread? That is clockwise to remove?

regular thread

don't use ether/starting fluid, use a thimble full of mix.

Make sure it's not flooded/wet plug.

Can be hard to start if choke don't close, it's inside air filter. But a shot of mix should get around that

 

[merc_man]

Carb cleaner is safer.

I use a spray oiler with some mix in it. Then its getting the lube it needs

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[Justin Taylor]

Thanks for the input, Hmm fly wheel key & compression...that should be easy to check.

Does anyone know if the flywheel nut is reverse thread? That is clockwise to remove?

Normal thread I would use a impact so you don’t have to use a piston stop

 

[merc_man]

Thanks for the input, Hmm fly wheel key & compression...that should be easy to check.

Does anyone know if the flywheel nut is reverse thread? That is clockwise to remove?

I would pull the muffler first. Thats easyest place to start.

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[fobicboy]

All,
Thank you for the suggestions. I was able to check the compression, on the first the pull of the starter rope it goes to 40psi , after the 3rd pull it peaks out at 60psi. Not sure if these values are within specification.

The flywheel key is not exposed, usually on other small engines I've worked on the key is visible once the fly wheel nut comes off. I took a picture, not sure how normal this is. Does anyone know how to pull the flywheel off? Regular 2 to 3 jaw puller work?

 

[cbfarmall]

Those are bad compression numbers. Pull the muffler, have a look.

Stihl makes a special puller that threads into the flywheel to pop it loose. I think it's available aftermarket, inexpensively.

Chris B.

 

[Mad Professor]

Probably not correct type of compression gauge for a saw. As mentioned a look in ex port will tell you if it's really only 60 psi of compression (scored piston/stuck rings).

Stihl makes a nice puller that threads into the flywheel. Not too expensive but knockoffs are cheaper.

The keys usually don't shear unless flywheel has been removed then not put back on correctly.

Make sure your plug is not fouled. It might not be sparking under compression.

Also look over ignition lead. They can get pinched if not routed properly and/or AV mounts worn out. If insulation is bad it can short when saw is in certain positions

 

[fobicboy]

Gents,
Thanks again for the insights. Ok, compression is low, pulling the muffler looks to be straight forward. Pulling the fly wheel is not, need to shop for a puller. Looks like I am going to need a service manual also so I'll start my request/ search.

Mad Professor... the ignition is giving spark and the spark plug is brand new. When I prime the cylinder it just does not fire, not even a pop or backfire. What are the AV mounts?

 

[Mad Professor]

Gents,
Thanks again for the insights. Ok, compression is low, pulling the muffler looks to be straight forward. Pulling the fly wheel is not, need to shop for a puller. Looks like I am going to need a service manual also so I'll start my request/ search.

Mad Professor... the ignition is giving spark and the spark plug is brand new. When I prime the cylinder it just does not fire, not even a pop or backfire. What are the AV mounts?

If saw was full of unburnt fuel a new plug can foul when you put it back in. Is it wet when you take it back out?

AV mounts are the rubber buffers that connect the powerhead to the fuel tank assy. They isolate engine vibrations from the tank/handles. When they wear out, the two assys can pinch the ign coil wire and the kill switch wire.

If you have a bare spot it might not short when you have the wire off for testing, or just short when you pull the recoil.

I had a 038 that started running ragged in a big cut. The coil wire was getting shorted when the AV mounts flexed. I changed the rubber in the AV mounts, then used liquid electrical tape and shrink wrap to fix the coil wire insulation.

Also check your kill switch wire/switch. It should only ground when switch is on off position.

 

[merc_man]

Gents,
Thanks again for the insights. Ok, compression is low, pulling the muffler looks to be straight forward. Pulling the fly wheel is not, need to shop for a puller. Looks like I am going to need a service manual also so I'll start my request/ search.

Mad Professor... the ignition is giving spark and the spark plug is brand new. When I prime the cylinder it just does not fire, not even a pop or backfire. What are the AV mounts?

Av is anti vibration mounts

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[KarlD]

Gents,
Thanks again for the insights. Ok, compression is low, pulling the muffler looks to be straight forward. Pulling the fly wheel is not, need to shop for a puller. Looks like I am going to need a service manual also so I'll start my request/ search.

Mad Professor... the ignition is giving spark and the spark plug is brand new. When I prime the cylinder it just does not fire, not even a pop or backfire. What are the AV mounts?

Anti vibe mounts; normally black rubber and if worn can cause excess flexing within the saw that can cause other problems

 

[Justin Taylor]

Gents,
Thanks again for the insights. Ok, compression is low, pulling the muffler looks to be straight forward. Pulling the fly wheel is not, need to shop for a puller. Looks like I am going to need a service manual also so I'll start my request/ search.

Mad Professor... the ignition is giving spark and the spark plug is brand new. When I prime the cylinder it just does not fire, not even a pop or backfire. What are the AV mounts?

No no no no don’t buy a puller all u need to do is hit the crankshaft with a hammer well that’s what I do

 

[Justin Taylor]

Take the muffler off and sends some pics

 

[fobicboy]

Muffler off and here are the pics. The cylinder walls look shiny, pretty much no serious scoring. One shot is from the spark plug hole the other is from the exhaust port hole. The piston has fine vertical scratches no deep scoring.