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

[Okie]

If it's fuel related the gas line and pulse line are dirt cheap. (and have those formed ridges on the lines creates a place for hairline crack that gets worse as the line warms. The lines are probably around 15 plus years old.

Give it a prime of gas when it quits for a re-start test.
Just giving you some insight as to what you are looking at carb wise. Kit costs around $20 so best to just get a replacement carb. Look on your carb for type, etc. I think those 028's used about 2 or 3 different type carbs and the parts place may ask you what type is on the saw now. Carb on those is easier to change out (replace) than it first looks if you have not been into such before. (watch a you tube video about removing the kill wire and the throttle linkage area)
I think you can get a OEM Stihl carb for around $30. (do not go with the cheapo $10 CHINA clone carb for your own saw) Ok to use a clone carb on Bro in Laws saw)

Really don't sound like a bad carb yet. (and maybe not a manifold boot)

 

[HarleyT]

Still, take a peek at your piston.......

 

[Wood Doctor]

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

I've run into that also with McCulloch and other saws. However, OP said he replaced the fuel line and the fuel filter (pickup body). As an experiment, he might try running a short while without the tank vent stem at all. The vent is supposed to just get rid of a pressure build up in the tank that fights the carb so that it cannot deliver fuel to the intake manifold.

Only other thing I can think of is a crankshaft seal that gives up after awhile, but that seldom happens on an 028 and usually it prevents startup.

 

[thill]

If it's fuel related the gas line and pulse line are dirt cheap. (and have those formed ridges on the lines creates a place for hairline crack that gets worse as the line warms. The lines are probably around 15 plus years old.

Give it a prime of gas when it quits for a re-start test.

Really don't sound like a bad carb yet. (and maybe not a manifold boot)

I replaced the gas pickup line and stone last year, but what is the "pulse line?" That sounds like something that has potential.
I'm very familiar with 2-stroke outboards, and in those, the pulse line draws vacuum from the #1 piston to drive the fuel pump. Is it similar on a chain saw? When those crack on an outboard, it causes all kinds of funny issues, some similar to this one.

Choking did work for a while today, which was encouraging.

Still, take a peek at your piston.......

What am I looking for on the piston? Signs of scoring?


Thanks.

 

[Mad Professor]

I replaced the gas pickup line and stone last year, but what is the "pulse line?" That sounds like something that has potential.
I'm very familiar with 2-stroke outboards, and in those, the pulse line draws vacuum from the #1 piston to drive the fuel pump. Is it similar on a chain saw? When those crack on an outboard, it causes all kinds of funny issues, some similar to this one.

Choking did work for a while today, which was encouraging.




What am I looking for on the piston? Signs of scoring?


Thanks.

Impulse line transfers vacuum from crankcase to operate diaphragm in carb that pumps fuel. Hooks up just below intake boot on the case and connects to the tank to passage to carb on an 028.

 

[Okie]

Actually called impulse line. You can see such on ebay for a 028 and review how to change on you tube.

The impulse line operates the fuel pump in the carb from crankcase pulses. It's the rubber line on the right side underneath the carb and has a snug friction fit when the carb is pushed into place. (when new)

AND YES, pull the muffler and check the piston. (for scoring) If a spark arrestor in the muffler is clogged it will cause the same symptoms. If you see a spark arrestor screen just leave it out and a clogged spark arrestor screen will eventually cause your piston to score, so you need to make sure it's ok.

Was typing at same time a the Professor

 

[rd35]

Make sure the bolts holding the cylinder to the crankcase are not loose. That could cause an air leak when the cylinder gets hot.

 

[Okie]

thill:

What cha tinkin or doin about the 028?

 

[devo20]

I suggest doing a pressure vacuum test. It is very hard to do when the saw is hot but I would want to rule out the possibility of the crankcase leaking when the saw heats up and all the parts expand. Its a possibility, I would rule it out by testing COLD and if it passes that test, re test when the saw dies.

 

[thill]

Guys,
Today, I went out and pulled the saw that's been sitting for a long time. Swapped ignition module with good 025 saw, just to be sure.

She fired right up and took down a small dead tree and cut it up like butter. After about 20 mins, she died, right on cue .

No amount of priming even got a bump. .

Pulled air filter and shot in some starter fluid, but not even a bump. Strange!

I'm thinking it time to find this pulse line and check the head gasket.

Really hate this!

 

[HarleyT]

An 025 coil?????

 

[HarleyT]

How did that happen?

 

[thill]

An 025 coil?????

Yes. Same coil on both machines, so i just swapped to eliminate that part from the equation.

Definitely not a spark issue, and compression stays same, and spraying fuel has no effect.

Could it be flooding? Good question!

 

[HarleyT]

Are you sure?

 

[thill]

Are you sure?

Sure of what?

Right after it died, I checked spark, (good and hot) checked compression, (160 psi) and i sprayed starting fluid into the carb, (No ignition) and i put in a new spark plug. (No ignition)

No change, not even a slight cough.

 

[HarleyT]

How does an 025 coil fit?
I'll admit that I never tried, but I am sure that the holes don't even line up.
Can you take a pic of your saw's flywheel/coil??

 

[thill]

Harley,
I actually had pulled the coil out of the box of parts I have collected between all the saws. I thought it was an 025 coil, but it turns out, it was one of the extras I bought for this 028 in past years. I wasn't trying to be misleading, just thought they were the same.

Good call!

But I'm still in a strange place. Have spark, compression, and I even supplied fuel after it died, yet it remained as dead as can be. It's been awhile, and it's probably cooled off, so I'm going to check to see if it starts back up.

What is so strange, is that it works flawlessly right up until it dies. Smooth, good idle, and very powerful. Then, blub, blub blub and then nothing.

Going out to check it again. I'll put on a headlight and cut up some wood and see how long it runs this time. Will report back in a while.

 

[thill]

Okay, we might be onto something...

Out of curiosity, I removed the top grub before starting, and the saw just does not want to run. It's kicked and run for a few seconds, but not well at all. Normally, it starts and runs flawlessly when cold, so this is a first.

Going back out to put the grub back in and see if anything changes....

 

[thill]

Went back, and pushed the grub back in, and it still doesn't run. Coughs 2-3 times, then shuts off. Not able to get it to rev at all.

It's getting too late, but I need to test everything tomorrow.
Here are questions I have:
1. Was pulling the grub what started this latest problem, or is a progression of previous problem?
Q- What normally happens if you pull a grub?

2. Where did this extra coil come from, and is it any good? Is this the original coil?
I'll reinstall the previous coil, and see what happens.

UGH.

 

[trains]

Post up a picture of the piston as HT has asked.

When you did the carby kit, how was the screen ? Have you taken the carb apart again, and checked for more bits that could block it up ? Did you remove the main metering jet, if not do so and check underneath it.

Still think that its the coil thats at fault, not unusual to have a problem with a new part if its aftermarket or not.
Edited to add, if your putting on old bits with unknown history, or forgotten history, how do you know that coil is ok, and that it was not doing exactly the same thing, as its classic ignition module failing symptoms.

Impulse line should also be checked as already mentioned.