Stihl TS 400 quickie saw bogging out

[Gwiz]

Borrowed saw from work; as I was leaving, boss said it bogs out. He was right.
Ran great for 8 or 10 minutes, then lost power, had no throttle response and finally died as I was pumping the throttle. I thought it was only when hot. I started it again in a few minutes, ran great for 1-2 minutes before bogging again. Couple minutes later, same thing. Doesn't seem to have to cool down to run good again, just won't run very long.
What causes bogging out like that?
Seemed to be 'four stroking' when it was running good. I have a tach, but haven't used it. I'm not going to rebuild anything, but would adjust the carb to tach or change the tank filter or something small.
I dumped the fuel out as soon as I got home, it looked somewhat milky. I put good gas in it.
Thanks for input
James

 

[PES+]

Check the fuel filter and the fuel line.

Best to replace the filter.

The fuel line if it is not soft or have holes will be OK

If the filter is off the end of the line in the tank you will need to open the carburetor and clean it out.

 

[pioneerguy600]

Got a fuel tank vent on it?
Pioneerguy600

 

[Lakeside53]

4-stroking? na -that's the igntion limiter. Set the H screw (it it has one) to 1 turn out and forget it.

Tank vent - check it.

Compression - check it...

Air filters (three). Make sure they aren't blocked and some fool tweaked the H screw leaner and leaner to compensate.

Ignition... the auto advance fails and they can get stuck in full retard...

Later TS400 have a second tank and filter - catches "fumes" but eventually fills and needs cleaning out. There is a second filter in that tank...