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

[Okie]

3 things for a run.

Compression
Ignition (at proper time)
fuel

You say you give it a prime of gas into the carb throat? and no pop
You say it has good compression
You say the spark looks good (and you subbed a coil from a parts box???????????

I would give it a new spark plug and a new magneto. (I've seen such aggravation from ignitions)

 

[SteveSr]

3 things for a run.

Ignition (at proper time)

I vote ignition as well. Seen this symptom on MULTIPLE Stihl 4137 trimmer self-contained (i.e. point-less electronic) ignitions. Runs for 15 minutes and then just dies. Let it cool off... rinse and repeat. A lot of these ignition system have small microprocessors in them to control the spark timing advance curve. Who knows what the aftermarket does with these. After it dies you may still have spark but at the wrong time! The only way to find out for sure is to substitute a KNOWN GOOD Stihl OEM ignition. You can probably find a good used one on FeeBay or from a member on this site.

 

[rupedoggy]

I'm pretty good with small engines

That is a VERY good question. I have no idea.

what is the "pulse line?

What normally happens if you pull a grub

 

[HarleyT]

Any good used 029/ms290 coil fits just fine. Any shop should have a stack of them laying around.

 

[Okie]

If yours is electronic ignition type here is 3 links for you to review a NEW replacement 0000 400 1300 ignition module and a spark plug is enclosed. Very reasonable prices.

https://www.amazon.com/Hilom-Igniti...nition+coil+replaces+oem++0000-400-1300&psc=1


http://www.lilredbarn.net/product-p/0000-400-1300.htm


https://www.ebay.com/itm/Ignition-C...h=item4b586fa410:g:T6EAAOSwb2lZzgQu:rk:1:pf:0

I would give it one of these NEW mags so as to eliminate ignition. What you describe is a symptom of ign system, especially electronic type mag's.

 

[GeorgiaVol]

Just my 2 cents.
I've had similar issues before. 1 was the coil, the other the fuel screen in the carb had gotten blocked. I would open the carb up and check it.

 

[SteveSr]

Just my 2 cents.
I've had similar issues before. 1 was the coil, the other the fuel screen in the carb had gotten blocked. I would open the carb up and check it.

Yea, but a fuel screen doesn't unblock itself when it cools off to allow the saw to run some more!

 

[GeorgiaVol]

Mine did. It was weird.

 

[rupedoggy]

Yea, but a fuel screen doesn't unblock itself when it cools off to allow the saw to run some more!

Maybe not but it can trickle small amounts past a partial blockage and run again for a little. What is the harm in checking the screen? Why come on here and poo poo someones ideas to help with a problem? Many times I see well meaning guys suggest the flywheel has slipped. I know that isn't the problem but let the guys learn. Mike

 

[HarleyT]

The passage under the screen can get partially clogged, especially from crud from the deteriorating fuel filter, and allow it to run pretty good until it is into some wood, where the clog leans it out, as the fuel cannot be delivered fast enough.
Which is why he should also look at the piston.

 

[rupedoggy]

Hey Harley, I have a great idea for you. Patent a glass front muffler so that we can check our piston after every use. Kind of like those fire stoves with the see through door. Mike

 

[HarleyT]

Good idea!
That is the only way some of these folks will ever take a peek at their piston!!
But then again, it would still be a lot of hassle to hold the saw up and look at it....

 

[HarleyT]

This saw should still be under warranty still, I would take it back to where the saw was purchased from, if any of the folks there are still alive!!

 

[GeorgiaVol]

A piston peek is one of the most basic checks for 2 cycle engine diagnostics.
Use fresh fuel
Clean the air filter
Don't run it if it screams

 

[rupedoggy]

I can see it now "my new saw came with the see through window. Can I use flame color to tune my saw?" "What is the correct mix to use in the see through saws"? LOL

 

[president]

The passage under the screen can get partially clogged, especially from crud from the deteriorating fuel filter, and allow it to run pretty good until it is into some wood, where the clog leans it out, as the fuel cannot be delivered fast enough.
Which is why he should also look at the piston.

Just had that happen,foam insert degraded and went through the system
2 screens and a tank flush later

 

[dustyz]

A piston peek is one of the most basic checks for 2 cycle engine diagnostics.

You can say that again. Worked on a ms290 for what felt like days. Finally found the carb side of the piston was shattered. No idea how the thing even ran. :-|

It's just too easy to check. From now on, it will be one of the very first things I do.

 

[Natster]

Good idea!
That is the only way some of these folks will ever take a peek at their piston!!
But then again, it would still be a lot of hassle to hold the saw up and look at it....

Liability there. "Well, me saw was runnin 'b'bout 12000 rpm, an I was gonna check me pistun..." And so reads the insurance claim...

 

[thill]

Gentlemen,
Thank you so much for your help!

After removing the grub made the engine stop running, the fact that I know compression is perfect hot or cold, the fire is strong, hot or cold, all your suggestions about it being fuel related started making sense.

When I started digging into this saw, I realized that I gave bad information at the beginning of this thread. I had NOT rebuilt this 028 carburetor, but it was the 025 that had been rebuilt. I had mentally ruled out carb issues because it runs so flawlessly when it runs. So I decided to immediately rebuild the carb. While shopping for a rebuild kit, I saw a replacement carb online for $16, so what the heck, I ordered it, too. Worst case, I have a backup.

When doing the swap, I noticed that the pulse line was only pulled about halfway onto the barb. Interesting! I also went back to the original coil and I replaced the grub line.

Once back together, I pulled the cord. Started instantly and ran well, as usual. But this time, she kept running smoothly for 2 hours of hard use.

She is fixed. It was definitely fuel related. I'm 50/50 between suspecting the pulse line and where the carb connected to the intake. The new carb came with a gasket for that place, and the original one didn't, so I'm wondering if that wasn't opening up when the saw got hot.

Half of me wants to install the old carb with the new gaskets and see what happens, but right now, I have a lot of wood to cut before worrying about that.

Again, thank you for all your help, and sorry for the inaccurate information.

 

[grizz55chev]

What’s a “ grub line”?