Stihl 028 runs great, then dies after 15 mins or so, every time...

[thill]

Have a Stihl 028 that I picked up used. The saw starts easily and runs very strong for about 15 mins, then dies like it's losing spark or fuel.

Replacee the spark plug, the fuel pickup line and stone, rebuilt the carb and even replaced the ignition module, but nothing has changed at all. Still runs great for 15 minutes, then dies. Let it cool completely, and it will do it all over again.

I'm almost at my wit's end with this one, and I need firewood for this winter!

Any thoughts or suggestions are greatly appreciated.

Thanks!

-Tony

 

[SEAM]

Defective ignition module (coil) or clogged fuel tank vent would be my first guesses...

 

[burnses]

boschitis strikes!

 

[Mad Professor]

When it dies give it squirt of gas w/AF off. If it pops/runs its fuel. Check vent. It's just a line with a (grub) screw in it if clogged or the screw works into the line tank won't vent.

If you've replaced ign. module, still check for spark right after it dies. Bad coils go bad , but sometimes they start going when they heat up, saw dies. When still HOT check your spark.

Has to be fuel or spark. Don't throw parts at it until you know where to go.

P.S. just for a check, pull muffler and have a look at P/C

 

[Okie]

When it dies give it squirt of gas w/AF off. If it pops/runs its fuel. Check vent. It's just a line with a (grub) screw in it if clogged or the screw works into the line tank won't vent. Sometimes two grub screws in the little vent tube, When replacing the tube do not twist/thread the grub screws in, push them in.

If you've replaced ign. module, still check for spark right after it dies. Bad coils go bad , but sometimes they start going when they heat up, saw dies. When still HOT check your spark.

Has to be fuel or spark. Don't throw parts at it until you know where to go.

P.S. just for a check, pull muffler and have a look at P/C[/QUOTE]
Take a gander at the Piston/cylinder.

Make sure that the saw is NOT getting hot usually due to running lean and quitting. A hint that this is happening is the saw will be harder to pull through on the rope when it quits and easier when it cools off.
When it's harder to pull through it's mainly because the piston skirt is swelled and rubbing on the cylinder and rapidly scoring the P/C.

 

[LoveStihlQuality]

Not sure if flooded or starved? Choke is the little spring loaded flap inside of air filter. Try running without.?

Sent from my SM-N900P using Tapatalk

 

[HarleyT]

I agree, look at that piston!!

 

[dmb2613]

 

[thill]

Gentlemen,
Thanks for the good suggestions! I will use the saw tomorrow, and when it acts up, I'll run some tests.

I'm pretty certain it's losing spark, not fuel, but I'll definitively find out tomorrow. I thought the replacement coil would have fixed that problem, but it still remains, which is very puzzling.

Should I do compression tests, or is there something I can look for/see with the muffler off? The saw is NOT harder to pull when it dies, BTW. It just gets weaker and weaker, and then won't start until it cools off.

And the saw does NOT feel like it's particularly warm in the hand. More like it's gotten up to normal operating temps, and then it shuts off. I thought maybe a cracked head, and making the fuel mix more rich would compensate, but in this case, the more fuel, the less it runs, once it starts to die.

I thought of a blocked vent, so I loosened the fuel cap to compensate, but it didn't make any difference. Removed air filter when it acted up, but no difference. Did the things listed in the original post, but no difference

I'm pretty good with small engines, but this one has me scratching a bald spot on my head!

-Tony

 

[Okie]

Yes, remove the muffler and gander at the piston. Do a cold compression test and another when the saw quits.

Have everything ready to do a spark test when it dies.

Does the engine stay smooth as it gets weaker? Does it just shut off like you flipped the kill switch?

Do you have a Infrared temp gauge?

Is that a old model 028 that has points and condenser? (under the flywheel)

I would do a compression test cold and compare to hot reading. The compression will go down on a warm/hot engine and the Stihl is getting weak if it's at or below 100 hot and suspicious if 125 hot or cold, but I have an old 028 in 125-130 area and it still starts/cuts good and rope pull feels good compression and piston not scored so I just keep on running it. It's a 30 year old saw.
You may know this: BUT you cannot use a automotive compression gauge, you will need a good accurate small engine compression gauge.
If when checking a chainsaw's compression and the gauge is lazy and low check another saw and see if the gauge will read correctly before going further. (quite common for small engine compression gauges to lie to you especially if you are not familiar with your tester and how to get a correct reading)

 

[thill]

Quote:
"Does the engine stay smooth as it gets weaker? Does it just shut off like you flipped the kill switch?"

It runs perfectly, then starts losing power, and within a minute or two won't restart. After maybe 10 minutes or so, I can get maybe a minute or so with it, and then it dies. After maybe 30-40 minutes, it will run flawlessly again until it repeats the symptoms, a but quicker than the first time from full cold condition.


Quote:
"Is that a old model 028 that has points and condenser? (under the flywheel)"

That is a VERY good question. I have no idea. If that is the case, then I will know what to do. I think this saw is from the late 1990's, but that is another good question for me to research.

I will pull my spark neons, temp gun and compression gauge out and test everything before and after. I have used the same comp gauge for everything, and it seems to read fine. It just takes a few more pulls for small motors to get a good reading, but it seems to work fine, as far as I can tell.

I'm feeling encouraged from all the helpful comments. Even if the saw is dying, at least I will know why.

I'll post after I get the testing done this evening.

Thanks!

 

[thill]

OK, have some baseline data on the saw:

Spark: Nice, hot spark. In fact, she started up for a sec on the first pull
Compression: 165 PSI after 5 quick pulls, but is an automotive type comp tester.
Temp: 89.3 F

I have to run out to a meeting, so it might be later tonight or tomorrow before I can run the saw long enough for it to die out, but I'll post as soon as I do with temp, compression and spark tests.

-Tony

 

[Kenskip1]

Gas tank vent clogged?

 

[Wood Doctor]

Gas tank vent clogged?

Yep, replace that tank vent tube. I ran into this five years ago. That was the problem. Could be cracked, loose, missing, clogged, or any of the above. That plastic tube and the set screw inside could be 25 years old or more.

 

[Okie]

Quote:
"Does the engine stay smooth as it gets weaker? Does it just shut off like you flipped the kill switch?"

It runs perfectly, then starts losing power, and within a minute or two won't restart. After maybe 10 minutes or so, I can get maybe a minute or so with it, and then it dies. After maybe 30-40 minutes, it will run flawlessly again until it repeats the symptoms, a but quicker than the first time from full cold condition.


Quote:
"Is that a old model 028 that has points and condenser? (under the flywheel)"

That is a VERY good question. I have no idea. If that is the case, then I will know what to do. I think this saw is from the late 1990's, but that is another good question for me to research.

I will pull my spark neons, temp gun and compression gauge out and test everything before and after. I have used the same comp gauge for everything, and it seems to read fine. It just takes a few more pulls for small motors to get a good reading, but it seems to work fine, as far as I can tell.

I'm feeling encouraged from all the helpful comments. Even if the saw is dying, at least I will know why.

I'll post after I get the testing done this evening.

Thanks!

Do not rely on neon spark testers, they will lie to you. Have another spark plug ready and a good method of grounding the body of the spark plug to see spark and set the gap at about .060 or pull the existing plug and look for spark. If you haven't already install another correct type spark plug.

Here is the type of spark tester I use, you can even rig this one in-line with your existing spark plug and watch the spark jump the gap or ground and watch. I've never tried to run a chainsaw with it in-line but I have on all kinds of Briggs engines. It is a Briggs 19051 or 19368. $8 with free shipping.

here is a link to view
https://www.ebay.com/itm/SMALL-ENGI...880083&hash=item1ea7ca19d0:g:rQkAAOxyqUpQ6VKQ

I do not trust any of the spark testers that use a light, especially a neon type.

AND you say the saw is a 90's model, it most likely is the magnetron ignition, no points. You say you replaced the ignition coil.
If you see a wire coming from under the flywheel connecting to the coil it has points. The non-points just has a spark plug wire and a kill wire. No wire connecting to the coil coming from under the flywheel. This indicates a electronic ignition and it's quite common for the electronic type coils to have yours symptoms.

Another thing. Pay real close attention to the spark gap jump both cold and when engine don't start. Look at it in a darkened place instead of bright sunlight.

I've got into two different NEW electronic magnetron coils for small engines in last few months, one would act like yours and the other would not even fire at all. Appears China is getting back at us Americans

Does your saw have the grub screw type vent tube? There are usually two grubs inside the tube. If so have you removed both the grub screws and tested or just remove the vent tube for a test?

 

[thill]

QUOTE:
"Do not rely on neon spark testers, they will lie to you. Have another spark plug ready...
...Another thing. Pay real close attention to the spark gap jump both cold and when engine don't start. Look at it in a darkened place instead of bright sunlight."

I've had some awful neons in the past. But for the last couple of years, I have used both the neons and the gap-type testers by CDI, and both work well. In general, I have found that these particular neons are very good for diagnosis, as they work while the engine is running, and the color changes depending on how "hot" the spark is. So I can often watch as an engine misses or dies out at a certain RPM. Very helpful, especially with more complicated systems that have power packs and EMM's.

But because of your suggestion, I'll use the gap-type tester instead of the neons, and check the jump distance before and after.


QUOTE:
This indicates a electronic ignition and it's quite common for the electronic type coils to have yours symptoms.... I've got into two different NEW electronic magnetron coils for small engines in last few months, one would act like yours and the other would not even fire at all. Appears China is getting back at us Americans

Now THAT is interesting! It WAS an aftermarket coil I used from Ebay, no doubt from China, after my Stihl dealer gave me a price of $145 for a factory coil, which seemed outrageous.

QUOTE:
"Does your saw have the grub screw type vent tube? There are usually two grubs inside the tube. If so have you removed both the grub screws and tested or just remove the vent tube for a test?"

Yes, it has the vent tube with grubs. No, all I have done so far is loosen the fuel cap when it died, to make sure it wasn't causing a vacuum. If the saw still has spark after it dies, I will pull the grubs out and try again. I hope it's that easy!

Again, thanks. I can't wait to get into this tomorrow after work.

-Tony

 

[Mad Professor]

Grubs/vent are easy to fix. Use quality line made for fuel if OEM is not handy/available. Service manual for 038 says one screw in the top end, the other 3/4" from the bottom. As mentioned, push do not screw them in place

Lots of used OEM coils about. Stihl used to lifetime warrantee them. A better bet than Chi-Com. Should be a lot of other model stihl coils that will work ( any that take universal # 0000 400 1300), might have to change/trim coil/kill wires.

 

[thill]

My customer this morning delayed until 1:00, so I went out to test the 028 some more.


Put saw on the gap tester and it would jump 3/8", but not 7/16" or 1/2".
170 PSI on the comp tester
I did NOT pull the grubs or vent line.

It started right up 2nd pull, and ran for a good half-hour this time, running smooth as silk through a large white oak. This really is one of my favorite saws. Then it started losing power, and within a minute it was dead and wouldn't restart.

Thinking about the fuel issue, I loosened the gas cap and tried to restart. Nothing. So I took over to the shop to see how things compared...

Temp on the head was 193 degrees, 187 on the spark plug.
Neons showed... Good spark???
Gap test showed it jumped 3/8" gap. HUH!?!?
Compression was 160 psi
No unusual tension when I pulled the cord.

With this information, I re-filled the gas and oil, (in case it's a cracked pickup line) hit the choke, and she started up for a second. HUH! I ran over to the wood pile, restarted and tried cutting. She ran, but felt a little weak, so I cracked the cap open and cut sideways, and she immediately shut down and wouldn't restart. Closed the cap and eventually got her restarted AFTER hitting the choke again. She kind of surged between more power, then less, then shut off again.

This time I ran over to do a temp and comp check. Temps this time were around 240 degrees on the head and plug, but apparently, it cools off pretty fast, because it dropped very quickly to 190 then 140. Compression still at 160 psi.


I seem to have good spark at all times, and the compression seems very good and consistent. It appears that this is a fuel issue, not a spark issue, which is a little surprising to me, since I have tried all of this before, and never got this far.

I have to run to my job now, but when I get back, I'm pulling the vent grubs and will re-test.

Here are some pics this time. The saw is in average, used condition, as you can see. Not beat up, but not super clean either. One shows the plate and what I think is the serial number. Is the number all the way to the right the serial number? Would 0000 967... mean it was made in July 1996?
Sorry for all the noob Stihl questions. I've run a Homelite Timberman 45 for the last 20 years, (has been a great saw!) and this is my first Stihl, although I have an 021 for limbs, and it runs flawlessly since I replaced the fuel pickup hose and stone.

Very appreciative of the encouragement and knowledge you guys have!

-Tony

 

[alabamatriker]

I have a Husky 51 that had same problem. Had it for years and ran great. One day started surging when hot and then would shut down. When I checked the fuel line, if broke in half in my hand. New line and it ran great again.

 

[Kenskip1]

How about a fuel line that is pinched in the bottom of the tank?