Stihl 025 not even trying to start

[OneStaple]

Hey all,

My dad brought his 025 over for some help diagnosing a non-starting problem. He said it ran fine about 6 months ago and idled nicely, but hasn't been run since. He uses only premixed fuel/oil (from HD). He said it was serviced about 4 years ago, and it would appear that they changed some things like the fuel line (can't really see the impulse line to know without tearing it down more). He said they put a new carb on at the time. He's run it a bunch since that servicing.

Before going towards a tear down, vac/pressure test, etc, I wanted to see if you all had suggestions on things to try.

When trying to start it, it doesn't even attempt to start. No cough, nothing.

Air filter was very dirty. We fixed that right away. Compression is about 120 psi. So decent, but not great. Spark plug shows spark when held against the cylinder. I tried pouring a little gas in the carb throat, but nothing changed. Butterfly valve on the choke opens and closes as expected.

Thoughts? Things to check/try?

Thanks,
Tyler

 

[HarleyT]

First, dump out the old fuel that was in it. Then with the plug out, pull the rope a bunch and thoroughly dry it out, then try the shot of fuel/prime again, without putting fuel in it.
See if you can get it to hit, then we can go from there.

 

[Wat n Tarnation]

Check the flywheel key.

 

[Captain Bruce]

Hey all,

My dad brought his 025 over for some help diagnosing a non-starting problem. He said it ran fine about 6 months ago and idled nicely, but hasn't been run since. He uses only premixed fuel/oil (from HD). He said it was serviced about 4 years ago, and it would appear that they changed some things like the fuel line (can't really see the impulse line to know without tearing it down more). He said they put a new carb on at the time. He's run it a bunch since that servicing.

Before going towards a tear down, vac/pressure test, etc, I wanted to see if you all had suggestions on things to try.

When trying to start it, it doesn't even attempt to start. No cough, nothing.

Air filter was very dirty. We fixed that right away. Compression is about 120 psi. So decent, but not great. Spark plug shows spark when held against the cylinder. I tried pouring a little gas in the carb throat, but nothing changed. Butterfly valve on the choke opens and closes as expected.

Thoughts? Things to check/try?

Thanks,
Tyler

Spark tester, not engine block ground. Spark degrades.

 

[J D]

120PSI compression is pretty low... if that's accurate, even if you get it to run it won't run too well. Might just be your tester though.
If it was running well when last used the next thing I'd do is pull the muffler to make sure that's not full of some kind of nest & take a quick peek at the piston

 

[Kidneycutter]

Not an expert but does it fire with gas down the cylinder. If so I'd be getting into the carb and making sure the needle valve hasn't got stuck or gimmed up. I've had this on a few saws.

 

[rls383]

Did you get the 025 running.???

 

[OneStaple]

Did you get the 025 running.???

Yes/no. We ran out of time to keep working on it when my dad was here, so he took it back to his place. We didn't fully diagnose or fix it. After taking it home, he decided to try to start it a couple weeks ago and said it fired right up and worked for cutting some things.

Sooo, I'd say that there's still a problem that needs addressing. Not sure why it started working. I'll hoping we'll have more time to work on it over the upcoming holidays so I can spend a bit more time with it.

Thanks,
Tyler

 

[lone wolf]

120PSI compression is pretty low... if that's accurate, even if you get it to run it won't run too well. Might just be your tester though.
If it was running well when last used the next thing I'd do is pull the muffler to make sure that's not full of some kind of nest & take a quick peek at the piston

This, it may be scored with that low compression reading.

 

[OneStaple]

This, it may be scored with that low compression reading.

Yes, I think that's a reasonable expectation. But I'd think the saw could still run, even if compression is on the low end. If compression was closer to 100, I assume it wouldn't run at all. The condition of the piston is certainty something I'd want to look at in the future.

I believe my compression tester to be fine. I measure in the 165psi range on my saws.

Tyler

 

[lone wolf]

Yes, I think that's a reasonable expectation. But I'd think the saw could still run, even if compression is on the low end. If compression was closer to 100, I assume it wouldn't run at all. The condition of the piston is certainty something I'd want to look at in the future.

I believe my compression tester to be fine. I measure in the 165psi range on my saws.

Tyler

So pull the muffler and lets see.

 

[Bob Hedgecutter]

So pull the muffler and lets see.

May not tell the full story?
Read back through and the filthy dirty air filter part- could be ingested fines scored up the intake side and compression drop from there- not too visible from the exhaust side?

 

[OneStaple]

So pull the muffler and lets see.

May not tell the full story?
Read back through and the filthy dirty air filter part- could be ingested fines scored up the intake side and compression drop from there- not too visible from the exhaust side?

Agreed. I'd like to look at both sides of the piston and see what were dealing with. Wouldn't be surprised if there's some scoring.

Hopefully I'll get a chance to do this in the next month and a half. There just wasn't time last time my dad visited to dig that deep into his saw.

Tyler

 

[Pythagorus]

Spark tester, not engine block ground. Spark degrades.

Ht may fire in the open but not be strong enough to give an effective spark when under cylinder compression'"In the old days" before the fantasies of some of the modern test equipment there was 'analogue' equipment for viewing spark of a spark plug but tested under compression.

I agree with the suggestions you pull the muffler and check it for operational airflow.

Odd ball things come up on chainsaws..e.g. in EVL's a worn crank seal can let compression into crankcase rather than hold in cylinders .

I'm 'surprised' you tried to run the saw without even cleaning the airfilter. That would have been my first action. Another would be to check the pickup at flywheel is ok. One suggestion was the 'key' at flywheel...thing is...more likely to get no spark if that broken enough for flywheel to slip from correct timing...or fail to turn. Some pick-ups can be adjusted a little to get further into the lines of flux. Spark plugs also can fail on their own condition even when gap 'looks ok'....and ,anyway...did you check and adjust the gap...for a start.

If the aircleaner has not been maintained the saw may not have been maintained ...maybe there is also damp sawdust in the magneto area.

You may, also, have wet the plug when pouring 'a little fuel' nto the carburettor.....of course these are all speculative. On the outcome I'd say you is saying "I'll work if I want to and right now that's not for you! ....so buggar-off and leave me alone". Be grateful for small mercies!....

 

[torch]

Ht may fire in the open but not be strong enough to give an effective spark when under cylinder compression'"In the old days" before the fantasies of some of the modern test equipment there was 'analogue' equipment for viewing spark of a spark plug but tested under compression.

It sounds like you are referring to the Colortune plug, made by a UK company called Gunsons. Still readily available and very popular in the motorcycle tuning community. It temporarily replaces a sparkplug and has a glass top to give a view of the combustion in real time. (Mixture is adjusted to produce a "Bunsen blue" flame colour, with a bit of yellow on acceleration). And yes, the presence of spark can usually be seen if the cylinder is missing.

I've never tried one on a chainsaw. I suspect it would not be particularly useful, particularly on a small saw like the 025. The plug itself is hollow and therefore adds volume to the combustion chamber -- not much effect on a larger 4-stroke, but it might be significant on a small 2-stroke, particularly if the objective is to evaluate spark.

Compressed fuel/air mix is better insulator than uncompressed free air and tends to quench the spark. The higher the compression, the higher the voltage required to make a spark jump a particular gap. A weak coil that still produces a spark across a plug gap held against the block may not produce enough voltage to spark inside the engine under compression; it might only require 2 to 3,000 volts to spark in free air, but anywhere from 8 to 15,000 volts inside under compression. (Google "Paschen's Law"). The added volume of the ColorTune could mislead one into thinking a borderline ignition is adequate.

I would suggest a spark checker. There are two basic kinds. One works in free air, with a screw adjustable gap. If the spark can jump say a 3/8" gap, there's ample voltage available, but if it barely jumps a 1/16" gap, you have a problem. The other style is inserted between the plug and the plug cap. It contains a light bulb that flashes if the plug actually sparks. Both styles work best in the shade or inside the garage.

 

[Pythagorus]

It sounds like you are referring to the Colortune plug, made by a UK company called Gunsons. Still readily available and very popular in the motorcycle tuning community. It temporarily replaces a sparkplug and has a glass top to give a view of the combustion in real time. (Mixture is adjusted to produce a "Bunsen blue" flame colour, with a bit of yellow on acceleration). And yes, the presence of spark can usually be seen if the cylinder is missing.

I've never tried one on a chainsaw. I suspect it would not be particularly useful, particularly on a small saw like the 025. The plug itself is hollow and therefore adds volume to the combustion chamber -- not much effect on a larger 4-stroke, but it might be significant on a small 2-stroke, particularly if the objective is to evaluate spark.

Compressed fuel/air mix is better insulator than uncompressed free air and tends to quench the spark. The higher the compression, the higher the voltage required to make a spark jump a particular gap. A weak coil that still produces a spark across a plug gap held against the block may not produce enough voltage to spark inside the engine under compression; it might only require 2 to 3,000 volts to spark in free air, but anywhere from 8 to 15,000 volts inside under compression. (Google "Paschen's Law"). The added volume of the ColorTune could mislead one into thinking a borderline ignition is adequate.

I would suggest a spark checker. There are two basic kinds. One works in free air, with a screw adjustable gap. If the spark can jump say a 3/8" gap, there's ample voltage available, but if it barely jumps a 1/16" gap, you have a problem. The other style is inserted between the plug and the plug cap. It contains a light bulb that flashes if the plug actually sparks. Both styles work best in the shade or inside the garage.

Hi...sounds as though we are 'on the same page'...and I know the testers of which you write.....I'm thinking of a different type...much larger than those little critters....There was one 'way back' which tested spark under compressor pressure...haven't seen one for over 50 years. The colour of the flame changes somewhat under the various condiiton. Some may still not understand that the fuel-mixture burns, it doesn't 'explode' ( in proper running) . As well, carburettors reduce engine speed by incrementally (or rapidly)closing the butterfly. Idling occurs and is adjusted by the enginebeing deprived of the fuel-air mix the carburettor has the capacity to otherwise allow.

 

[OneStaple]

It sounds like you are referring to the Colortune plug, made by a UK company called Gunsons. Still readily available and very popular in the motorcycle tuning community. It temporarily replaces a sparkplug and has a glass top to give a view of the combustion in real time. (Mixture is adjusted to produce a "Bunsen blue" flame colour, with a bit of yellow on acceleration). And yes, the presence of spark can usually be seen if the cylinder is missing.

I've never tried one on a chainsaw. I suspect it would not be particularly useful, particularly on a small saw like the 025. The plug itself is hollow and therefore adds volume to the combustion chamber -- not much effect on a larger 4-stroke, but it might be significant on a small 2-stroke, particularly if the objective is to evaluate spark.

Compressed fuel/air mix is better insulator than uncompressed free air and tends to quench the spark. The higher the compression, the higher the voltage required to make a spark jump a particular gap. A weak coil that still produces a spark across a plug gap held against the block may not produce enough voltage to spark inside the engine under compression; it might only require 2 to 3,000 volts to spark in free air, but anywhere from 8 to 15,000 volts inside under compression. (Google "Paschen's Law"). The added volume of the ColorTune could mislead one into thinking a borderline ignition is adequate.

I would suggest a spark checker. There are two basic kinds. One works in free air, with a screw adjustable gap. If the spark can jump say a 3/8" gap, there's ample voltage available, but if it barely jumps a 1/16" gap, you have a problem. The other style is inserted between the plug and the plug cap. It contains a light bulb that flashes if the plug actually sparks. Both styles work best in the shade or inside the garage.

I've used Colortune on an old motorcycle years ago. I wasn't particularly impressed with it, but then again, that motorcycle had lots of "personality" (issues, really). I hated balancing the four carbs, and it seems like they always needed to be tweaked. I agree that Colortune likely wouldn't work well on a saw.

For the spark checkers, my assumption is that the in-line tester with the light bulb would probably work better since it's using the actual cylinder/compression conditions of the saw to verify spark, correct?

Tyler

 

[torch]

For the spark checkers, my assumption is that the in-line tester with the light bulb would probably work better since it's using the actual cylinder/compression conditions of the saw to verify spark, correct?

The light bulb is definitive -- there is a spark if the light flashes. There is not if the light does not. However, it does not reveal why there is no spark -- eg: cracked or fouled plug won't spark. The adjustable gap tester verifies that the ignition side is capable of delivering sufficient voltage and gives an idea how strong the ignition system is -- longer gap, stronger ignition. So both devices have their uses.

 

[torch]

In the interest of science, and since I own both an 025 and a selection of ColorTune plugs, I tried the 14mm motorcycle version in the saw this afternoon. The saw does run, rev and idle, although response is notably crisper with the regular plug reinstalled. Idle mix was fat (orange) and 4-stroking, leaned out (Bunsen blue) as it revved up and a touch rich (flecks of yellow) at WOT. Didn't have any wood handy to try it in though.

 

[ihookem]

The saw got flooded real bad and would not start. I did thin with my 441 a few weeks ago . I cleaned the air filter, put new plug in and new gas. It didn't fire at all. The next morning I was ready to take it to the dealer, ,,, just thought I'd give it one more shot . I took a pull and it popped like always. Another pull and it ran flawless. It is a fussy saw , but the only realistic problem was is that it was all flooded out.