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

 

[tlmartin84]

How much money do I stick in this thing while I have it apart?

 

[SteveSr]

Did a compression test....right at 142 psi.

Here's some pictures....not seeing anything in the fuel delivery...some trash in the tank but filter and hose looks good.

Any chance this could be an ignition problem? Plug looks good, correct gap, and lights up when pulling rope.

View attachment 1214113

These types of fuel pickups have a piece of foam in them that is KNOWN to disintegrate over time and plug up the inlet screen in the carb.

Time to pull the bottom off of the pickup and look in the carb screen for debris.

 

[cookies]

How much money do I stick in this thing while I have it apart?

View attachment 1214225

oem hose and filter...35
aftermarket carb of decent quality 40-60 bucks or try your local dealer possibly 80 for oem or the version they can get you?

 

[buzz sawyer]

How many times should you pull it for the test?

I pull until the gauge stops moving. Maybe it's the picture angle but that plug gap looks very wide. I had a problem with an 028 bogging but only when hot - it was the coil.

 

[SteveSr]

Inside Carb....

View attachment 1214136

I don't see the carb screen in that 1/4" diameter hole in the top right. Without a screen a passage could be blocked with crud or decomposed foam from the pickup screen.

 

[tlmartin84]

How much money do I stick in this thing while I have it apart?

 

[tlmartin84]

How much money do I stick in this thing while I have it apart?

 

[Jay Hansen]

I'd pressure test the fuel line, p&v test the engine. Assuming that tests ok, clean the carburetor, change the filter and put it back together.