Stihl 028 AV Super, stumbles at WOT.

[Gord404]

I would pull the carb and see if that little filter screen is not full of crap and pressure test it before you pull it down- put a new sprk plug in it as well- possably a compression issue as well, not enough to burn mix properly- pull the muffler and tak e a good look

 

[tlmartin84]

Under 140 compression is iffy on a lot of small older cc saws. 130 I would think is to low on an 028. My guess you have blow by your rings the gas coming back out the carb. Likely enough debris got through your air filter over time and wore things out in your cylinder. Probably at least need rings and make sure you have a good air filter and keep it clean daily.

Dude Im wrong...

10 pulls it is around 142
It maxes out around 160 at 15 pulls

 

[stihltech]

You guys and your compression gauges. Piston and ring visual inspection is much more important.
Stihl has not used that fuel filter since the late 80s. Noted for disintegrating and plugging the screen at the carb inlet.
May just be the picture but the plug gap looks off. I don't use clear plastic hose on the vent as it tends to melt into the threads over time.
Is the pulse hose providing a good pulse at the carburetor?

 

[tlmartin84]

Inside Carb....

 

[cookies]

You found your likely culprit, replace that fuel filter too...if the fuel hose is squishy replace it