stihl 025 difficulty

[Dexter]

My Stihl 025 (old version of 250) is acting up.

It is simply lacking torque. I've tried multiple chains. With a sharp chain it pulls through wood pretty well -- but slowly. It has a new spark plug. The fuel mix is fresh, and precisely measured to 50/1. It idles ok. Idle-throttle-setting and idle-mixture are adjusted (there is no high speed mixture adjustment.) The air filter is clean. I cut at high altitude (about 8500 feet) and have used the saw up there for the past 12 years.

But: Now, I have to put too much load on the saw before it "2-cycles" properly. Under no load, it revs to high rpm nicely, with light missing/4-cycling. This is as it should be; a fully revved saw that hits on every stroke WHEN UNDER NO LOAD is usually at too lean a mixture. But when I put the chain to the wood, it brings the rpm down too far before it "hits" on every stroke. I spend a LONG time per cut.

What'cha think? Magneto, maybe? Is that a big deal to do yourself?

Any suggestions would be appreciated.

Regards,

Dexter

 

[savageactor7]

hummm the 025 goes back to the early 80's when they made saws to last...those saws are almost bullet proof. I wonder if that's the original drive sprocket? Try replacing that if you don't know how, it easy, check back and someone will tell ya.

edit...it's only a $3 part...so buy 2.

I have an 041 I got back in '77 that's still cuts wicked excellent.

 

[fire_N_ice]

Fresh fuel. .How fresh? are you using octane of 89 or higher?. If it is brand new gas, it may be bad gas from the pump. . .Fuel line pinched, clogged? If it sat for a while did you dump the old gas and run till stalled?

 

[Dexter]

Well, I buy gas at high altitude where, for the low ambient air pressure, regular gas is cracked to an 85 octane rating. I know the manual says 89, but honestly, I bought the saw new a long time ago, and at 8500 feet it's run great on regular for at least 12 (maybe 17?) years. I've tried 89, a couple of times and could hear or feel no difference. No popping or detonation in either case. BTW, fresh fuel means out of the pump that week, and mixed. At the end of the cutting weekend, I put the remaining mix in the "beater" wood truck and mix a new batch the next time out.

"Savageactor7"'s fuel line suggestion might be worth looking at. I use carb cleaner occasionally, but I've never pulled and cleaned the line itself.

Does the magneto ever fail on these things? Could it be electrical?

Dexter

 

[Dexter]

Sorry, that was fire_n_ice with the pinched fuel line idea...

SavageActor7: Original sprocket with chain marks, but remarkably little wear.

I'm 'gonna take apart and clean the heck out of the fuel system. I'll mix up some 89 octane and try it. If it still has problems, I think I'll try the magneto. Unfortunately, they're about $60 at the local Stihl store.

Dexter

 

[Redox]

Before you go to all that trouble, pull the muffler off and check for carbon buildup. It may be that all those happy years of use has left a little residue.

It doesn't sound ignition related to me as that would probably show up more at idle, but anything is possible. Where's Cmonstart when we need him???

Chris

 

[savageactor7]

Dexter also fish out the fuel pick up in the tank with a wire. Carefully pull the filter up threw the cap and check that out, it'll unscrew, spray insides/outside of cylindrical filter with carb cleaner and blow clean with some compressed air...and blow out the vent in the gas cap too just in case.

 

[FatttFire]

I have tried the same thing except for the clutch/ drive sprocket. My Stihl 041 has seemed to have just lost its balls. I have tried almost everything and still no luck. Looking at a new o44, bu thats $750

 

[bill*67]

hows the compression? check the basic things first.

 

[cmonSTART]

Ya, compression and cylinder wall condition would be my first thing to check. After you know that's good I would be looking at the fuel system as others have suggested. If you have no high speed adjustment, a good cleaning/rebuilding may be in order.

 

[Dexter]

I have an old automotive "hold-against-the-plug-hole" compression tester which I had not thought about. But, if the compression is down -- and I don't know if the manual lists proper compression range -- is it a sleeved cylinder? Or will I have replace the cylinder/engine? AAHHhh!

 

[smokinj]

My Stihl 025 (old version of 250) is acting up.

It is simply lacking torque. I've tried multiple chains. With a sharp chain it pulls through wood pretty well -- but slowly. It has a new spark plug. The fuel mix is fresh, and precisely measured to 50/1. It idles ok. Idle-throttle-setting and idle-mixture are adjusted (there is no high speed mixture adjustment.) The air filter is clean. I cut at high altitude (about 8500 feet) and have used the saw up there for the past 12 years.

But: Now, I have to put too much load on the saw before it "2-cycles" properly. Under no load, it revs to high rpm nicely, with light missing/4-cycling. This is as it should be; a fully revved saw that hits on every stroke WHEN UNDER NO LOAD is usually at too lean a mixture. But when I put the chain to the wood, it brings the rpm down too far before it "hits" on every stroke. I spend a LONG time per cut.

What'cha think? Magneto, maybe? Is that a big deal to do yourself?

Any suggestions would be appreciated.

Regards,

Dexter

ok if you know how to tune your saw,and your not sure what to do next i would take it to the dealer most the time and can be chepier. I would also check the chain is it done right

 

[Jack33]

Lot of years on that saw, most likely worn ring/low compression. Still runs well without load so a simple and cheap ring swap will probably fix it up. Check your compression, ideal given the age would be 130ish psi or better. Less than 110ish probably wouldn't run at all.

I have an old automotive "hold-against-the-plug-hole" compression tester which I had not thought about. But, if the compression is down -- and I don't know if the manual lists proper compression range -- is it a sleeved cylinder? Or will I have replace the cylinder/engine? AAHHhh!

You need a screw in tester with a valve in the end. Check it hot and keep pulling till the gauge stops rising.

REPLACE the $3 fuel filter if it has not been done recently. This does not sound like an ignition problem. IMO, your $60 would be better spent on a proper compression tester, air and fuel filters, fuel line, impulse line, and a ring.

 

[Dexter]

I feel stupid: I totally forgot about rings. 'Sounds like sage council, Jack33. I assume 2-cycle pistons would only have one ring -- compression? At any rate, I'll do all but the ring before I cut this weekend, and change-out ring (if bad compression) next week. 'May get a shorter bar too, for blocking the smaller wood.

It's getting chilly in the mountains now. 'Nice cutting wx.

Best Regards,

Dexter

 

[cmonSTART]

Let's see, I think on that saw I would expect to pull somewhere around 120 to 150 psi. If things are indeed worn, they sell a cylinder, piston, ring kit for it.