Another Stihl 025 Mystery

[Fish]

Had a neighbor's saw the other day, he needed it bad, flywheel nut was loose.
Sheared the key. I thought, no biggie, I have a dozen or more of those saws on the shelf. Turned out, I reused his old flywheel, the other flywheels wouldn't even get the saw to pop. I just glanced at the keyways, the keyways were way off. Noted that the coil looked different too. Just lined up the keyway, torqued down his nut, and sent him on his way.

 

[Wood Doctor]

OK, I have made some minimal progress. First, I removed the pull cord cover and cleaned out the flywheel area of all grime. Then I checked the ignition module and it looked like the gap was too small. I removed it, cleaned it up, reset the gap at 0.01", reassembled, and checked again for a spark. Looks good.

Tried starting but still no pop. So I tried the old standby of adding a teaspoon of gas to the cylinder through the spark. This time it fired and ran 5 seconds but refused to keep running. So I tried the second standby of adding fuel through the carb with the air filter removed. Once again, it would pop and run about 5 seconds and then die.

So, I removed that carb and tried another one. Same exact results. When removing the previous carb, fuel jetted out the line like a siphon, so we know the carb is pumping OK. I let it sit for an hour and then checked the plug again. Plug is dry as a bone. Pulled several more times on choke and fast idle but again no pop. Removed and checked the plug again -- dry as a bone. Tried a third carb with the same results as the other two.

My conclusion is that fuel is making it to all of the the carbs but not one of them is sending the right mixture (or any mixture at all) to the combustion chamber. Is it possible that I have three bad carbs? Hard to believe, but that's my conclusion. Before I throw these carbs away or buy another, I may try them on a running 025 and see if they work, but at this point, I'm worn out.

Any other suggestions? Is it possible that the flywheel is loose or the timing is off if it ran for a few seconds when goosed?

 

[Onan18]

I would check the impulse line from the cylinder, they are a bone of contemption on this model.

Joe

 

[t4driller]

OK, I have made some minimal progress. First, I removed the pull cord cover and cleaned out the flywheel area of all grime. Then I checked the ignition module and it looked like the gap was too small. I removed it, cleaned it up, reset the gap at 0.01", reassembled, and checked again for a spark. Looks good.

Tried starting but still no pop. So I tried the old standby of adding a teaspoon of gas to the cylinder through the spark. This time it fired and ran 5 seconds but refused to keep running. So I tried the second standby of adding fuel through the carb with the air filter removed. Once again, it would pop and run about 5 seconds and then die.

So, I removed that carb and tried another one. Same exact results. When removing the previous carb, fuel jetted out the line like a siphon, so we know the carb is pumping OK. I let it sit for an hour and then checked the plug again. Plug is dry as a bone. Pulled several more times on choke and fast idle but again no pop. Removed and checked the plug again -- dry as a bone. Tried a third carb with the same results as the other two.

My conclusion is that fuel is making it to all of the the carbs but not one of them is sending the right mixture (or any mixture at all) to the combustion chamber. Is it possible that I have three bad carbs? Hard to believe, but that's my conclusion. Before I throw these carbs away or buy another, I may try them on a running 025 and see if they work, but at this point, I'm worn out.

Any other suggestions? Is it possible that the flywheel is loose or the timing is off if it ran for a few seconds when goosed?

Have you put carb kits in all the carbs and cleaned them very good. Without and ultrasonic cleaner sometimes you don't get it clean enough. Need to take apart and clean them again. Is the tank vent good?

 

[kyle.kipple]

Impulse or intake.

 

[Onan18]

Impulse or intake.

Impulse

 

[Fruecrue]

throttle linkage, master control lever all doing their thing? I had one once not close the choke properly and wouldn't start.

 

[Wood Doctor]

Choke lever is doing fine. Tank vent is fine. You find out very quickly when installing the carb that the choke has to be in the on position just to get the wire control lever in place. I'll check the impulse line from the cylinder as Joe recommended, but as he knows, that's a small bear because the saw has to be taken apart in order to get to it.

Say, I wonder if I could ship this to someone who loves working on 025's and 250's? I already have five or six saws in the same size and weight class that start and run flawlessly. Not even Ted Williams or Ty Cobb batted a thousand.

 

[kyle.kipple]

Choke lever is doing fine. Tank vent is fine. You find out very quickly when installing the carb that the choke has to be in the on position just to get the wire control lever in place. I'll check the impulse line from the cylinder as Joe recommended, but as he knows, that's a small bear because the saw has to be taken apart in order to get to it.

Say, I wonder if I could ship this to someone who loves working on 025's and 250's? I already have five or six saws in the same size and weight class that start and run flawlessly. Not even Ted Williams or Ty Cobb batted a thousand.

I'm always game for a project.

 

[Fruecrue]

With the carb off, if you roll the crank you should be able to tell if you have any impulse line....,um.... impulse.

 

[blueberrymuzik]

I'd be happy to help out on this one if you would like to send it here.

 

[Wood Doctor]

OK, Fruecrue, I'll try that. Carb is off again. If I'm not mistaken, the impulse opening to the carb is a hole in a small flap on the lower right corner of the manifold. The fiber gasket that covers it has a small opening that leads into the carb. These are all unblocked.

I pulled the starter cord and the engine actually popped with what little fuel was still in there. What am I supposed to notice happening with this opening as I turn the crank?

 

[Fruecrue]

You want alternating positive and negative pressure as the crank rolls

 

[Wood Doctor]

You want alternating positive and negative pressure as the crank rolls

Can this be done with the spark plug removed? The saw has lots of compression and turning the crank is tough.

Would there be enough pressure to blow out a wad of cotton? I need a sensor indicator of some sort.

 

[Fruecrue]

With piston at bottom, plug out, hold your thumb over the intake and roll the motor. That impulse hole in the manifold should move air in then out

 

[Wood Doctor]

With piston at bottom, plug out, hold your thumb over the intake and roll the motor. That impulse hole in the manifold should move air in then out

When the plug was in, the engine tried to run for awhile. Apparently there was still enough fuel in the combustion chamber left over from previous starting attempts to fire it for 10 seconds.

With the plug out and the intake blocked with my thumb, I notice no air moving at all through that small impulse opening. I placed a small chunk of paper towel over the opening and it never budged.

Looks like the impulse hose from the jug may be completely blocked or perhaps totally contaminated. Does that seem to be the problem? If it's blocked, is there any way to unblock it without taking the saw apart?

 

[Fruecrue]

I've also seen the 021/023/025 saws flood due to rich low jet settings. Even some that are stamped 1 turn out on the plastic require only 1/4 turn out on the low screw

 

[Fish]

Send it to me, I've got scads of old saws for any parts.

 

[Fruecrue]

That impulse line could be plugged, kinked, ripped or disconnected. I would disassemble as little as possible to get a view of what's going on. Was this saw disassembled before failure or just quit one day?

 

[Wood Doctor]

That impulse line could be plugged, kinked, ripped or disconnected. I would disassemble as little as possible to get a view of what's going on. Was this saw disassembled before failure or just quit one day?

It just quit. I've never had it apart. That's why I also agree that it's the impulse hose that gave up, likely blocked. I don't think it's flooding out. The only way any fuel is getting into the chamber is whenever I put it in there with a squeeze bottle.

The thing is, whenever I have run into a cracked impulse hose in the past, the engine will start and run but have no power. I've never seen a faulty impulse hose shut it down completely and prevent a cold start.

Unfortunately, any Stihl requires a major disassemble to get to that impulse hose -- even the professional line. Either the jug has to come off or the tank housing. So you choose your poison. Rats!