Stihl 025 won't continue running

[skippymud]

Hello All

Stihl 025 will not stay running. Requesting assistance, words of advice

Has spark, and compression of 112. No visible scoring from intake or exhaust sides. I have two carbs; one ORIG, one bought on eBay that includes a high-speed ADJ jet. Neither will get this one running. Low miles after inspection of the clutch teeth and bar but they could have been replaced at some point. On partial choke, it runs for just 5 seconds then dies. Start again on partial and I get another 5 seconds. Choke off no run at all. Tried both carbs and same *exact* result. Got to be something else, but what?

Your points will be well-taken. Give it to me

 

[Woodslasher]

Your tank vent looks kinda funny so that may be part of it, and have you pulled out the fuel line and checked for cracks, checks, etc?

 

[Junk Meister]

Coils ban be ELUSIVE.

 

[drf256]

Sounds like it’s starving for fuel. I’d swap out the fuel line and filter.

I recently had an oem filter crack at the neck. Issue was found after many hours of work on the saw.

Your tank vent, it looks odd. If the saw runs for a bit and then leans out it could be the vent. It should run for more than 5 seconds though, then run normally again after you open the fuel cap If it’s the vent.

Coils are usually all or none and get worse when saw gets hot.

 

[Junk Meister]

Sounds like it’s starving for fuel. I’d swap out the fuel line and filter.

I recently had an oem filter crack at the neck. Issue was found after many hours of work on the saw.

Your tank vent, it looks odd. If the saw runs for a bit and then leans out it could be the vent. It should run for more than 5 seconds though, then run normally again after you open the fuel cap If it’s the vent.

Coils are usually all or none and get worse when saw gets hot.

My 025 saws were the unusual. The 2 with the Black plastic throttle control rod seemed to break down slowly. I bought a used OEM (bay) and it faded the same way and after a few years I had forgotten the frustrations of the first coil. The second 025 black control rod had the coil fade the same way. The old red rod one is still going without issue as is the MS250. This all spanned over several years, and these saws aren't used a lot. I Agree with coils are like light bulbs. and these two 025s' are the reason for my post #3

 

[hacskaroly]

Your tank vent looks kinda funny

Your tank vent, it looks odd

The vent tube should be fine, it is missing the grub screw that lets air in and prevents fuel from coming out when the saw is on its side or upside down. Grub screws are only a couple of dollars a piece. Most of the time when the old line breaks, rots or is pulled out during repair and lost, people don't think about the little screws and just replace it with a piece of tubing. I did this once and fuel leaked all over the place when I put the saw on its side to work on it.



I have this set up on my 066. My 046 on the other hand has two different fuel tanks and both of them have something different than this. Some IPLs will show multiple options that may have been used through out the years the saws were manufactured.

 

[Brad Button]

Your compression is pretty low, and the piston skirt is worn which is what pulls the fuel. Besides that have you done a leak-down test to see if it is sucking air someplace? It also could be the impulse line, on the 025 they look like a fuel line that goes from the bottom of the cylinder and plugs onto a nipple under the engine housing. I have seen those come off the nipple. I would do a leak-down test first if you haven't already.

 

[Junk Meister]

The vent tube should be fine, it is missing the grub screw that lets air in and prevents fuel from coming out when the saw is on its side or upside down. Grub screws are only a couple of dollars a piece. Most of the time when the old line breaks, rots or is pulled out during repair and lost, people don't think about the little screws and just replace it with a piece of tubing. I did this once and fuel leaked all over the place when I put the saw on its side to work on it.

View attachment 407390

I have this set up on my 066. My 046 on the other hand has two different fuel tanks and both of them have something different than this. Some IPLs will show multiple options that may have been used through out the years the saws were manufactured.

When you put/install the grub screw DO NOT screw/thread it in. it will cut its' own threads and seal off the venting . PUSH the screw in so air is able to pass ...

 

[skippymud]

Hello All

Thanks much for your words of advice!
Compression is low. And yep, the breather tube does look funky. Found the grub plug/SCR and installed
What I failed to mention. I replaced: impulse line & filter, coil, plug, fresh fuel mix
So I tore this puppy down last night just to see more. Found a wasted flywheel key. Go figure. Should have checked that upon my initial inspection
My plan now is to clean the grime, replace the crank seals while I'm here, reassemble w/new key and do leak down and compression tests. Will let ya'll know the outcome - Ken

 

[Canadian farm boy]

Since you have the saw torn down and with that low compression you might wanna check your ring gap and inspect the piston skirt wear.

 

[skippymud]

Ring Gap - Good point - Got it, CFB. Piston skirt and crown look really good by the way

When I first started wrenching on this 025, I noticed clearly that pulling the recoil was VERY difficult, which yes(?) could be attributed to the busted key. Is that possible or probable? Compression should be upwards of 160psi. Let's see

In cleaning mode while I await crank seals and key from AMZ

 

[drf256]

Does your compression tester have a shrader valve?

 

[skippymud]

Hi DRF. It does not. Why? Curious Ken

 

[Canadian farm boy]

Your compression tester should have a shrader valve in the end that screws in to the spark plug hole. If the shrader valve is at the gauge end of the hose essentially the air volume in the hose is then part of your combustion chamber and you’ll get a low reading.

 

[skippymud]

Hmmm, that I understand. Keeps the compression reading close to the chamber, hence a more accurate figure [from/in] the chamber

Right now, what I am looking for is a more/less figure, to know how far to go in my rebuild with 110 being quite marginal. Though the skirt and chamber really look pretty and not scored at all. Me happy so far and so excited to get this running

At this point, I will get the key and see where this goes. I love this *s-word. Keep it coming

Did you see the dart in my previous picture. Nice touch, uh?

 

[drf256]

It’s pretty rare to have a saw with a non-scored oem top end and very low compression. Figured it was your tester.

 

[Chainmale]

Your compression is pretty low, and the piston skirt is worn which is what pulls the fuel. Besides that have you done a leak-down test to see if it is sucking air someplace? It also could be the impulse line, on the 025 they look like a fuel line that goes from the bottom of the cylinder and plugs onto a nipple under the engine housing. I have seen those come off the nipple. I would do a leak-down test first if you haven't already.

I've seen them come off due to bad av buffers and/or being yanked on when pinched

 

[Czed]

Hi DRF. It does not. Why? Curious Ken

My tester just like that one is wildly inaccurate
I'd personally replace seals and at least rings since your that far into it.
Meteor has a nice piston kit for those
10 year's ago i rebuilt a 025 for my 84 year old neighbor
He's 94 now and still running it.

 

[skippymud]

Hiya Czed. If I do rings, need I hone the cylinder or may I leave that alone?

 

[Czed]

Hiya Czed. If I do rings, need I hone the cylinder or may I leave that alone?

Scotchbrite or similar just break the glaze
Don't hone it can ruin the cylinder.