Stihl 026 dying after running fine for 5-10 mins

[johnbinsc]

Hi again experts,

I am a homeowner on a wooded lot who occasionally takes down his own trees.

My 30 year old Stihl 026 starts and runs great for 5-10 minutes.

Then it either dies on idle or I shut if off to do something, and when I go back to restart it, I cannot get it started.

But if I wait until the next day, I can get it to start easily and it runs for another 5-10 minutes.

It has had this problem for a while, so I did a carb rebuild, but it still has this problem.

I thought it might be vacuum lock on the gas tank, but I can remove the tank vent and then replace it and it still will not start.

So it seems to be related to the saw engine getting hot.

I saw one suggestion on another site that my gas line might be pinching off when it gets warm. It is the original gas line, and it is on my to-do list to replace it, but I have not yet.

What do you all think of that theory?

Is there anything else I should look at? What are the chances that the pulse line is failing when the saw gets hot (warm)? Of course, that is also the 30 year old original.

Thanks,
John

 

[Bob Hedgecutter]

Sounds like the symptoms of a dying coil.

 

[johnbinsc]

Very interesting!
Do you or anyone have the resistance specs on the coil so I can measure it? Part # 000-400-1300
Will that coil resistance measurement tell me anything, or is it always good, even for a bad coil?
The genuine Stihl coils are pricey!
Are the inexpensive aftermarket coils on Amazon etc any good, or is that just a waste of time and money?
And finally, is this heat related coil failure usually mean the coil itself is bad, or should I look for other ignition issues before I buy the new coil?

A lot of questions, I know. But you guys have the depth of experience...

 

[stihltech]

Coil resistance went by the wayside with ignition modules, which you have.
Get an in line spark tester. When it quits, see if you lose spark. The you will know.
Don't forget to check wiring. When it loses spark, disconnect the switch wire at the coil. That will tell you if it is the issue.

 

[Bob Hedgecutter]

Forget the testing this and that with meters and stuff.
Start the saw run it hard for 10 minutes till it cuts out and refuses to start and whip the plug out to check for spark- or have a spark tester in your pocket that fits between cap and plug to show a bulb lighting at each rotation of the flywheel- if no spark or very weak spark- coil is likely cooked.

Incidentally- what numbers and letters are on your spark plug?

 

[lone wolf]

Two things came to mind when I read this ,first
Pull the muffler and check the piston for scoring.
The coil!
Also
Are you cutting in very high temps, it could be vapor lock?

 

[Joepro]

Don't waste money on aftermarket coils either. Genuine only

 

[Old2stroke]

Can you check the compression? Starts cold but won't start hot could be due to low compression (less than 100psi)

 

[grizz55chev]

Fuel, comp, spark in that order. Fuel is easy, pull the air cleaner when it quits and give it a wiff of gas or starter fluid if it starts and dies, skip the spark theory.. Spark is also easy, as stated in earlier posts. Pull the muffler and check the condition of the piston-cylinder, and muffler itself for blockage . Good luck and post your progress .

 

[johnbinsc]

Thanks to all for all the expert advice.
I will try to do a spark test once it is hot and cutting out on Friday.

For the compression test, should that also be done while the motor is hot and cutting out?

I actually have a good compression tester, but I may or may not have the right adapter. We'll see.

I'll also get the numbers off the plug and report back.

Thanks again!

 

[stihltech]

Spark is number 1 test for a hot failure. Follow procedures above.
Diagnose first, buy needed parts later.
Save money (and frustration). Sorry Chickanic.

 

[StihlsawuserMS361]

Tips hat to StihlTech

 

[ZeroJunk]

If it was me I would put a $12 Chinese coil on it. If that solves the issue buy an OEM.

Just how much hair do you want to pull out. Cutting, scrambling around trying to check spark with an inline tester and a decent one is expensive. Or, burning your fingers on a hot plug.

PM me your address and I'll mail you one Monday free.

 

[newworld]

air leak

 

[guym3]

Getting some good advice here. If it runs for 10 minutes before it dies, then it probably isn't a fuel supply issue. Chinese coils can be fine (and are cheap). I've replaced one on my 026 and it's fine now. So I'd first replace the spark plug as that costs very little. Then the coil. After that I agree that an air leak is quite likely. Look at Vintage Engine Repairs on YouTube for how to pressure test your saw. Good luck.

 

[stihltech]

So it's easier to change coils than check spark? Spark checker? Plug with really wide gap.
Diagnosing is still cheaper.

 

[Old2stroke]

Be wary of AM coils, they seldom work. Might produce a spark but the timing can be so far off, the engine won't run.

 

[lone wolf]

Be wary of AM coils, they seldom work. Might produce a spark but the timing can be so far off, the engine won't run.

 

[ZeroJunk]

So it's easier to change coils than check spark? Spark checker? Plug with really wide gap.
Diagnosing is still cheaper.

I have a couple of those cheaper spark testers, but they are made in such a way it is impossible on some equipment to fold it back when the boot and plug are maybe an inch apart. Homeowner Stihl weed eater for instance. Also, he could cut with the Stihl in place and see what the fire does in real time. You can do it with the Stihl, but they are not cheap. And, there may be others. But, my cheap ones are not very usable.

So, if he wants to buy a good tester that is easier. If he doesn't, messing with the plug in a hot saw is no fun.

 

[stihltech]

I guess I am just trying too hard. All I know is an inline spark tester and a large gapped plug (mine has an alligator clip for ground) have saved a lot of time {and guessing} when diagnosing hot no starts and hard starts.