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.

 

[Sidecarflip]

One thing I NEVER do is open my fuel or oil caps without using a small bristle paint brush to remove all the debris around the filler caps prior to opening them. I carry it in the pocket of my bib overalls. 45 years on my 028 and nothing in either tank except what is supposed to be inside. The 028 in my humble opinion was best saw Stihl ever produced. That and my 090 that I don't use anymore as it's too heavy. Interestingly, the 028 still has the original plug in it. I've cleaned it and gapped it a couple times but it's still the original. Could also be the canned fuel diet in receives as well.

 

[Hman1024]

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

Depends, kind of like growing a garden in my mind, I don’t make money, come close to break even but I know where the food comes from type of thing. I own a couple of the 028s and with some minor replacement of things you are encountering, saw might go another 20 years. My normal calculation is to spend up to half of its worth, but then again I might have a chainsaw problem.

 

[tlmartin84]

Depends, kind of like growing a garden in my mind, I don’t make money, come close to break even but I know where the food comes from type of thing. I own a couple of the 028s and with some minor replacement of things you are encountering, saw might go another 20 years. My normal calculation is to spend up to half of its worth, but then again I might have a chainsaw problem.

Mine seems to use an excess of bar lube. After cutting it leaves a pretty good puddle compared to my other saws.

Have you ever had to deal with that?

 

[stihltech]

So the question is do you want to spend 500 to 700 on a new saw, or do you want to put around 200 into this one?
Parts are getting less available for the 028 every day (OEM). I know they can be found on the internet.
I would do the things mentioned here. Clean up the carb and install a kit. I have seen that amount of corrosion still work.
Would I do it in the shop? No, because I could not guarantee it.
Would I try it my own saw? Sure.

 

[tlmartin84]

So, if I want to rebuild this saw....at this age where do I start?

If I pull the cylinder and split the case, do I replace bearings? Or are the older bearings better than new ones?

Clean the cylinder and re-ring? With it holding 160psi do I eve bother?

The carb is a walbroWT-16B, I bought it brand new 10 years ago so Ill try to rebuild it, not a fan of the Chinese stuff....

 

[oldercut]

Looking for where to start diagnosing....


Saw has had a lot of new parts in the past 10 years, carb, fuel filter and hose, vent hose, air filter, clutch etc.


Saw is stuborn to start after sitting for awhile, Ive found pumping the gas to pull it up prior to starting it helps.



Anyhow, used the saw about 6 months ago with no issues. Picked it up this evening to go work a tree, ran fine for about 10 minutes, blocked about 6 cuts in a 24" tree.



It started to bog almost as if the chain binding. Pulled it up, let it recover and it bogged again.



It idles fine, will pull to wide open throttle, will stay there for about 5 seconds and then bogs and stumbles.



Clean filter, sharp chain, good gas, the vent and pickup hoses are all good.

Your photo of spark plug looks very light. Have you tried enriching the
high speed mixture just a bit ?

 

[VinceGU05]

So, if I want to rebuild this saw....at this age where do I start?

If I pull the cylinder and split the case, do I replace bearings? Or are the older bearings better than new ones?

Clean the cylinder and re-ring? With it holding 160psi do I eve bother?

The carb is a walbroWT-16B, I bought it brand new 10 years ago so Ill try to rebuild it, not a fan of the Chinese stuff....

get it running right before worrying about replacing bearings etc. check spark plug gap, rebuild carby and filter as mentioned and try again.