Old Stihl 025. Cranks but won't run.

[N80]

I inspected the piston rings and side and they look amazingly good. Not sure about spark but right before I replaced the fuel line it was cranking and running but just for a second so assuming spark was fine then. Not a bad idea to replace plug anyway so will do that.

 

[N80]

I'm wondering if I didn't dislodge the rubber boot that connects the carb to the cylinder. Anyway, its all coming apart. Unfortunately the to-do list has intruded on my piddling time.

 

[dodge man]

There are some long screws that connect the carb to the cylinder. It’s possible it came loose but I doubt it. It could have a tear in it. It’s tough to check for spark. I usually take the plug out and try to hold it close to something metal on the saw and look for spark. Dim light can help. What usually happens is it shocks me instead. It sounds like your piston is good, I’d check for spark and try anew plug, I had a plug go bad once.

 

[dodge man]

A picture of the boot in the first pic. You can also see the corrugated line that could be a source of a leak hooked to the boot. The second pic shows the metal plate and long screws, the boot is hidden behind the saw body.

 

[PILOON]

I'll toss out another idea.
The weighted filter at the end of the pick up tank hose might just be crudded up enough to prevent fuel pick up.

 

[N80]

Sorry guys. Missed the last two posts. @PILOON , I have replaced the filter. No help.

I have torn the saw completely down with the exception of the crank case/piston assembly. Everything is thoroughly cleaned.

I can see nothing wrong.

I looked at all the cheap Chinese replacement carbs and rebuild kits and was about to pull the trigger on one of those when I ran across a new OEM Walbro carb for $40. That's about 3x the price of the knock-off carbs. Not sure if it was worth it but it is on the way. Most reviews said it worked perfectly with no adjustments. We'll see.

Will replace the spark plug and the charge tube (whatever it is called). The fuel line and fuel vent tube and fuel filter and air filter are all new.

If this does not work, I'm giving the saw to my son-in-law's brother who is a wiz with chainsaws and buying an electric one for home duty which is all this saw ever did since I got a larger Stihl for my property.

Will update when completed. Assuming I can get it all back together.

 

[N80]

Okay, got it all back together except the carb....a small miracle.... Should be quick and easy to pop the new one in when it gets here and see if I've wasted $40.

 

[N80]

Installed the new carb. It is OEM. After a few pulls it turned over. Switch choke to open. One pull and it fires up. Responds to throttle inputs and then 5 seconds later it quits and will not restart. I could cry.

That is the exact same problem I started with. Very disappointed and frustrated. So it was probably never the carb to begin with.

There are three things that I can think of to replace 1) The impulse tube (which looks perfectly fine. 2) The spark plug which is not old. 3) The carb gasket. It looks fine but a new one did not come with the carb.

I guess I could replace the magneto but I just don't see how that could be the case since it runs for a few seconds.

I'll do that and then I give up. Which is a shame. It is nice and clean and has a shiny new carb.

One other thing is the rubber elbow that attaches the carb to the cylinder. I inspected it and it looks fine. I wonder how hard it is to replace. It is very firmly attached to the cylinder.

 

[5030]

Sounds like a coagulated carb to me. Go get a replacement carb on Flea Bay and call it good and replace the fuel line and in tank strainer too.

 

[5030]

Read you last comment. You need to replace the in tank strainer too.

 

[BlackOps]

i have another brand saw but 2 weeks ago started and full run stalled. many times. tried everything. took it in and the guy said coil was gone. he is waiting for the part. that is all he said. the new kid is very unfriendly unlike the old owner who retired2 yrs ago. guy seems to not have parts or take forecer to get anything. just an off comment. so maybe that could be the issue with your saw.

might be so far off i sound ridiculous. but the symptoms seem very similar.

 

[N80]

@5030 Tank strainer replaced already. Only thing left in the fuel system to replace is the impulse tube.

 

[N80]

@BlackOps Could be the magneto. They're not expensive but if I keep replacing things I could have just used the money to buy a new saw. I'm already in about $80.

 

[BlackOps]

i understand. i have had to make that call 2-3x in my 70 yrs. better to buy a new and start again. i was just explaining what i am going through now. sounded similar to your experience.

 

[Ford850]

You might have done these, but they are the most common causes for your symptoms:
Check the muffler to be sure it isn't plugged.
Replace the impulse line as suggested earlier. (plenty of articles and videos online showing how to do this)

 

[dodge man]

I posted a pic earlier of the tube that connects the carb to the engine. It also shows the impulse tube. They just slide on but are probably on pretty tight. I reused mine on my rebuild. Get a new spark plug, I had one go bad once, but that’s probably not the problem. I’d say it’s the ignition module or a air leak.

 

[5030]

@5030 Tank strainer replaced already. Only thing left in the fuel system to replace is the impulse tube.

Think I'd do that (replace it) Don't take much in the way of a compromised impulse tube to starve that tiny diaphragm in the carb and keep it from pulsing. No pulse equals no fuel.

 

[N80]

I will replace the impulse tube. It is not hard to do but requires another tear down because it isn't very accessible. No big deal. New spark plug too.

Muffler is clear.

Couple of thoughts: When it cranks it cranks easily and runs normally for 10-15 seconds then stops as if flooded (has to sit for a while and then will restart). Pull the plug and it is wet. So it doesn't seem to me it is spark or fuel that is the problem.

So now I'm wondering if it is an internal issue. From the exhaust port the piston side and rings look great. But, maybe it is scored where I can't see it, or cracked or a hole burned in the cylinder?

Anyway, new impulse tube and new spark plug and then it goes to my nephew if still a no-go.

 

[BlackOps]

and then he'll have a saw that is no good too. heh heh

 

[N80]

He’s a bit of a wiz with saws. He rebuilds them and modifies them. So if there is an internal issue he’d find it.