Stihl 025 has me stumped

[Tim Berframe]

I have a 18 year old Stihl 025. Has less than 75 hours of use (3 cords / year for 10 years then basically nothing for past 8 years). Always started 3 pulls after sitting for a year or more - not this year. It started but ran terrible and was unusable. Opened the carb and it was plugged with green slime.

Assuming ethanol troubles, I just bought a new carb. Wouldn't start.

Changed fuel line, filter, checked intake boot(it is fine). No start.

Spark seemed weak so I changed coil, plug, and spark plug wire. Strong, hot blue spark. No start.

Changed base seals and sealed up bottom real carefully, new impulse line. No start.

Did compression test. 1 pull 60psi; 2 pulls 90 psi; 3 pulls 120psi; by 10 pulls 150 psi (this may be because of fuel now in the cylinder?) So, I have at least 120 psi.

I have good fuel supply - a nice white vapour with every pull.

The piston and cylinder look brand new. I can see cross hatch on the cylinder and the piston skirts have no wear or even discoloration on them. I didn't measure the ring gap cause I couldn't find a spec. Tiny bit of carbon on top of piston.

So, I have fuel, compression, and spark. That only leaves timing. The key on the flywheel is cast into the flywheel and is fine.

Pouring gas into the cylinder or into the air intake with a new, dry plug doesn't even try to kick. Dry base with choke and start lock etc etc like usual doesn't even try to kick.

So, my question is : Is it possible that the new coil is mismatched to the flywheel so that ignition timing is off? I have spent hours trying to find anything on line that would list specific pairs of part numbers. Unfortunately, I tossed the original so can't check part number. The replacement Stihl coil # is 400-1306. The book says the factory flywheel is 1123_400_1203. Is there a different flywheel to get me going?

 

[L34]

I would say a spark problem.If you have comp and put fuel down Carb,if spark OK it should at least pop.Even with timing out I think it should pop,may pull rope out of your hand.
I just got an 038 to fire by putting fuel down Carb and it hadn't been going for 5 years.
Is the plug wet after you try and start it?
Cheers,Chris.

 

[rd35]

If you are getting a white vapor from the exhaust it sounds to me like the carb is set so rich it won't fire. I'd run the H and L needles all the way in and then back out one turn only, pull the plug and crank it a few times to dry out the cylinder AND crankcase, re-install the plug, and crank it with no choke! May take several pulls, but it should eventually pop if this is the problem. I would even consider setting the saw on the bench turned upside down with the spark plug out and the piston at bottom dead center for a few hours. (I did just this and got a problem saw to start once when nothing else worked....after a couple of hours there was a puddle of gas on the bench....but she fired right up!)

 

[jltrent]

When on choke to start make sure the choke is fully closed.

 

[backhoelover]

Ring gap for all stihls is 1mm

 

[backhoelover]

That information is in the stihl Engine fault manual

 

[Tim Berframe]

If you are getting a white vapor from the exhaust it sounds to me like the carb is set so rich it won't fire. I'd run the H and L needles all the way in and then back out one turn only, pull the plug and crank it a few times to dry out the cylinder AND crankcase, re-install the plug, and crank it with no choke! May take several pulls, but it should eventually pop if this is the problem. I would even consider setting the saw on the bench turned upside down with the spark plug out and the piston at bottom dead center for a few hours. (I did just this and got a problem saw to start once when nothing else worked....after a couple of hours there was a puddle of gas on the bench....but she fired right up!)

No, its not out the exhaust. With plug out to check spark, I get a good fuel vapor spray out the spark plug hole. Carb screws were factory set at 1 turn out. I did try at 1/2 turn out. I've never flooded this saw or any of my other equipment at 1 turn out before.

 

[backhoelover]

Try a diff plug

 

[Tim Berframe]

Ring gap for all stihls is 1mm

Thank you, good to know. I should have measured it while I had it apart and found the spec later....

 

[Tim Berframe]

Try a diff plug

Not the plug. I have used 3 or 4. They all yield a hot blue spark.

 

[Tim Berframe]

Ring gap for all stihls is 1mm

So, is 120 psi compression low enough to cause a non-start? My old ski-doo rotax 2 strokes would struggle to life at 85 psi (ran terrible but would definitely pop) and 120 was the new compression they started at.

 

[Tim Berframe]

I would say a spark problem.If you have comp and put fuel down Carb,if spark OK it should at least pop.Even with timing out I think it should pop,may pull rope out of your hand.
I just got an 038 to fire by putting fuel down Carb and it hadn't been going for 5 years.
Is the plug wet after you try and start it?
Cheers,Chris.

Yes, fuel flow is fine. White vapor out the plug hole plus blue spark on plug equals a little fire ball in my face.

 

[Bobby Kirbos]

Could it be the plug wire?

With the plug pulled, the wire is in a position where everything in the wire assembly makes correct contact. Once you put the plug back in and connect the boot it is possible that the wire no longer makes contact with the clip at the plug, or perhaps there is a spot on the wire that is worn out and the wire is shorting to the saw body.

? ? maybe ? ?

 

[Conquistador3]

So, is 120 psi compression low enough to cause a non-start? My old ski-doo rotax 2 strokes would struggle to life at 85 psi (ran terrible but would definitely pop) and 120 was the new compression they started at.

All 025/MS250 I've seen ran between 120 and 150psi. It's not a high compression engine and will "easily" come to life at 120.

 

[HarleyT]

There are different flywheel/coil combinations, you might not have them matched properly.

 

[a. palmer jr.]

Very possible the key in the flywheel might be sheared, you'd have a nice spark but not at the right time.

 

[Tim Berframe]

Could it be the plug wire?

With the plug pulled, the wire is in a position where everything in the wire assemble makes correct contact. Once you put the plug back in and connect the boot it is possible that the wire no longer makes contact with the clip at the plug, or perhaps there is a spot on the wire that is worn out and the wire is shorting to the saw body.

? ? maybe ? ?

I don't think so - its all brand new... The cap snaps on real tight and makes a good connection.

 

[Tim Berframe]

Very possible the key in the flywheel might be sheared, you'd have a nice spark but not at the right time.

As stated in my original post, flywheel key is fine...

 

[Tim Berframe]

There are different flywheel/coil combinations, you might not have them matched properly.

So this is my very question. I have spent hours searching online for anything that shows paired part numbers. The replacement coil is Stihl genuine part number 400 1306. The parts book pdf I have shows the same for the saw. So, what would be the flywheel part number that matches? (The baffling thing is that one would think if the new coil has same # as original, then the original flywheel should match)

 

[a. palmer jr.]

Every saw I worked on and squirted a little fuel mix in the cylinder would start if it had a good spark unless the compression was low (below 90). I've sometimes had to take a timing light to check for the spark being on time.