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I have a Stihl MS460 Artic chainsaw it will run strong for 20 minutes then it starts bogging out looses power and cuts out.
This all started after I put a 36" bar and a ripping chain on this saw. I am using it for my Alaskan Chainsaw mill that I built.
After the saw cuts off if I let it sit for two minutes it will start back up and run for another twenty minutes before it cuts out again.
So far I have pulled and cleaned the carburetor some micro fine saw dust in there, checked the piston and rings both looked good so I did not do a compression test.
Cleaned the fuel tank and filter ( filter was put in last year). I did find a lot of fine saw dust clogging the tank vent removed and cleaned it out with carb cleaner and compressed air.
I thought for sure this would be it, but it was not.
The impulse and fuel lines are the new green ones they look OK very soft and flexible.
Normally I would think it was a coil but a bad coil has to cool down before it will start again I can restart in a few minutes.
Air filter and spark plug are clean
Any ideas on what to check next? Or how to trouble shoot this problem?

I would check for spark when it dies. Sometimes a coil doesn't have to cool much to start working again.

If you are ripping logs lengthwise, it seems to me you are putting this saw to pretty extreme use. Most chainsaws get a break fairly often, whereas yours might not.

I wonder if it could be overheating if it starts right up again after a short rest.

Wouldn't hurt to check to see if the cylinder fins are all clear and any filter that it might have to keep sawdust out of the cooling air stream is not restricted.

Check the clearance (tooth profile) on the chain teeth. I suppose you would be aware of an overheated saw chain, but... Also is the lube feed working. On my Husky you can watch the spray by holding the chain tip next to a log or branch. The two strokers produce torque a ways up the RPM scale and are weak down low so will stall out if tooth profile or lube are not right. You know this already...just some thoughts.

ILENGINE said:

I would check for spark when it dies. Sometimes a coil doesn't have to cool much to start working again.

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I checked the spark before I started the saw it was white/blue the saw cut off after 7/8 of a tank of fuel rechecked the spark and it was the same refueled and it started right up again ran for another ten minutes and cut off again still the same spark.
I am thinking the carburetor diaphragm is causing it it was a little stiff when I cleaned it.

motoman said:

Check the clearance (tooth profile) on the chain teeth. I suppose you would be aware of an overheated saw chain, but... Also is the lube feed working. On my Husky you can watch the spray by holding the chain tip next to a log or branch. The two strokers produce torque a ways up the RPM scale and are weak down low so will stall out if tooth profile or lube are not right. You know this already...just some thoughts.

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New .63 skip tooth chain on a new 36" bar
Oiling on saw is great also have a additional auxerilry oiller on the saw mill that drips oil on the nose of the bar.
No dirt or debris in fins on the cylinder head
I could hook up a single wire tachometer to the saw to check the RPMS
Picked up a new fuel filter and spark plug yesterday on my way out to wire a friends barn so I had no more time to check on the saw.

To beat on the teeth profile. I remember that teeth are ground "chisel tooth" for lumber milling, not angled. Does this sound familiar? Try another coil. Lots of stuff inside to fail from heat and vibration.

motoman said:

To beat on the teeth profile. I remember that teeth are ground "chisel tooth" for lumber milling, not angled. Does this sound familiar? Try another coil. Lots of stuff inside to fail from heat and vibration.

Click to expand...

I will try a new coil I just won one on EBay for $4.25 cheap trouble shooting for a OEM coil
When you break it down the saw is only cutting out when hot.
You need fuel, air, and spark to run.
Being hot would not effect the fuel or air so it would have to be spark
Normally when a bad coil gets hot the insulation breaks down and will start to short out when it cools it will work again until it gets hot.
This may be a coil just starting to go bad. It has never been a issue before because regular cutting the saw would get a break.
My only other thought would be the fuel or impulse lines are too soft and could possibly be colasping restricting fuel flow.
Thanks all for the help I will post back and let y'all know what I find.

More than insulation breaks down. It's the little chips in the circuit. IMO a $5 coil is not likely to last unless it is somehow a used Stihl. What does a new Stihl coil cost? I hope it works out for you.

The trick to working this one out is how does it "cut out" ?
If you are having fuel starvation it will tend to rev faster but loose power.
If you are loosing spark it generally misses a little then dies.

You may have marginal rings as well that loose tension when they get too hot then a few seconds of contact with the bore cools them enough to make a reasonable seal again.
A partially blocked muffler will do the same, eventually the little bit of exhaust that does not make it out of the muffler each stroke builds up enough to choke the saw.
I have had a couple of these, they had me jumping through hoops for weeks.
One was a partial blocked exhaust port, that saw would run at idle all day but cut out after about 5 minutes of WFO load and the other was a carbon build up inside the muffler

I replaced the tank vent and the fuel cap, I had the saw in the back of the pick up it got warm gas was shooting straight out of the center hole. I had suspected a fuel issue because it was cutting out as described above the saw is running great now with no issues.
My best guess is that micro mine sawdust that I had cleaned out of the tank vent was getting stuck closed
Thanks all who posted great advice