High Quality Chainsaw Bars Husqvarna Toys

Another Stihl 025 Mystery

Wood Doctor

Edwin
Local time
6:04 AM
User ID
846
Joined
Feb 9, 2016
Messages
2,399
Reaction score
8,360
Location
Omaha, Nebraska
Country flag
These Stihl 025 engines really stump me. I imagine the MS 250's do the same thing now and then. Here's the problem and associated observations:

(1) The engine has great compression -- over 145 psi. Rings are fine.
(2) The engine has a good spark but will not start and not even pop.
(3) Four carbs have been tried, including one that has no hours on it at all.
(4) The spark plug is getting fuel -- always damp when removed after several starting attempts.
(5) The carb gasket is new, fuel line is new, fuel filter is new.

What do you suggest?
 

kyle.kipple

Get busy living or get busy dyin...
Local time
7:04 AM
User ID
2445
Joined
Jan 9, 2017
Messages
120
Reaction score
261
Location
Ohio
You need spark, compression and fuel. You say you have great compression with a wet plug. How are you checking for spark? If the flywheel key checks out good, then I'd be looking for a donor coil to test on it.
 

Wood Doctor

Edwin
Local time
6:04 AM
User ID
846
Joined
Feb 9, 2016
Messages
2,399
Reaction score
8,360
Location
Omaha, Nebraska
Country flag
Simple, traditional check for spark: Jumper wire from plug threads to cylinder with plug inserted in boot. Good spark, plainly visible. It's there, believe me. Flywheel key is also intact and nothing is loose. This saw ran a whole year and then stopped suddenly during a buck cut, dead as a mackerel.

Frankly, I have never seen any other Stihl saw do this. Give them enough compression, a spark, a good carb, good pickup body, and a good fuel line, and they all run. Even with a lousy impulse hose or bad carb gasket, they will at least start. This one does not.
 
Last edited:

big t double

You can call me Teddy Eastwood.....
Local time
6:04 AM
User ID
372
Joined
Jan 1, 2016
Messages
1,359
Reaction score
6,985
Location
.
Vac/pressure test performed?
 

DELETED (Struggle)

Pinnacle OPE Member
Local time
6:04 AM
User ID
265
Joined
Dec 26, 2015
Messages
596
Reaction score
1,577
Location
iowa
If it was vac tested someone forgot to remove seal between muffler and head

Provided timing is correct and a different spark plug has been tried
 

brushwacker

Super OPE Member
Local time
7:04 AM
User ID
2485
Joined
Jan 18, 2017
Messages
246
Reaction score
338
Location
NW IN, USA
Country flag
+1 timing is way off or when you reconnect to the spark plug some thing could be pulling apart the circuit or could you be pinching a wire somewhere ? Surely the switch is on ? No 2 bare wires being pushed together by a cover being reinstalled ? Probably not as complicated as it seems.
 

Chainganger

Super OPE Member
Local time
6:04 AM
User ID
994
Joined
Mar 5, 2016
Messages
297
Reaction score
646
Location
Minnesota
Spark arrester plugged burn it with a torch

Could be flooded, I have 2 of these and they flood super easy and even with the plug out will not dry up for hours
 

kyle.kipple

Get busy living or get busy dyin...
Local time
7:04 AM
User ID
2445
Joined
Jan 9, 2017
Messages
120
Reaction score
261
Location
Ohio
You've eliminated compression being an issue so I would focus on spark and fuel delivery. youve tried several different carbs so I would like to think its not that. But for sh*ts and gigs, try to un hook the fuel line from the carb and block the end off. Squirt a drink down the throat and try to start it. That will rule out the carb feeding to much and flooding if it doesn't pop.
 

blueberrymuzik

Lesser Known OPE Member
Local time
6:04 AM
User ID
52
Joined
Dec 23, 2015
Messages
82
Reaction score
110
Location
SW Missouri
Sounds as if it is badly flooded. Take the carburetor off. Crank the engine until the piston is at or near the top of its stroke. Tip the saw up and see if fuel runs out of the intake port. Then take a blow gun and blow air through the intake for about 60 seconds. Put a dry spark plug in the cylinder and try to start. If it was badly flooded there will be enough residual fuel to get a pop. You should be able to put the carb back on and go from there.
 

Onan18

OPE Sponsor
GoldMember
Local time
7:04 AM
User ID
344
Joined
Dec 30, 2015
Messages
4,444
Reaction score
24,735
Location
Georgia
Country flag
Simple, traditional check for spark: Jumper wire from plug threads to cylinder with plug inserted in boot. Good spark, plainly visible. It's there, believe me. Flywheel key is also intact and nothing is loose. This saw ran a whole year and then stopped suddenly during a buck cut, dead as a mackerel.

Frankly, I have never seen any other Stihl saw do this. Give them enough compression, a spark, a good carb, good pickup body, and a good fuel line, and they all run. Even with a lousy impulse hose or bad carb gasket, they will at least start. This one does not.


It takes four times more energy to fire a plug under compression than atmosphere. You need an adjustable air gap spark tester, with the plug in the cylinder and the tester in line it should be able to jump a 6mm gap with a good blue spark.

Joe
 

angelo c

Coal Member
Local time
7:04 AM
User ID
362
Joined
Dec 31, 2015
Messages
2,919
Reaction score
11,552
Location
Peoples Republic of North Jersey
Edwin,
Take a look behind the carb mount and confirm the impulse line is connected. Damn things act funny if they are a little loose or leaking. Beyond that if you wanna play "endless swap" I have a couple good running 250's just sitting that you can mix and match parts with till your heart finds the true meaning of love.
lemme know where to send one ifn ya want.

Im betting on flooding though. this series is a known "NO BURP" saw.
 

jmester

Pinnacle OPE Member
Local time
7:04 AM
User ID
1769
Joined
Aug 28, 2016
Messages
1,144
Reaction score
3,386
Location
MD
Country flag
As mentioned above. I would look into the ignition module. Have seen those modules come loose and rub the flywheel causing them to run funny or not run at all. But still show spark. I have also noticed on that series that the shim behind the carb will deform if the carb is over tightened and cause an air leak. Hope it helps
 
Top