Help? 028 AV Super spitting gas out the carb

[Cascadium]

Hi folks,
I have a Stihl 028AV Super that I inherited from my FIL. He said it never let him down.
Well I had to buy a new coil, and rebuild the carb, and change all the hoses.....but I've used it a lot since, and it was working great.
Compression is good, stiff. He was a contractor, not a fire-wood cutter etc, so i don't think it's worn out.
It got stolen too, and the cops brought it back to me. Which made me happy 'cuz I think about him whenever I use his 028.

But trying to use it this season... it won't rev out. It starts & idles OK, but this is full throttle.
It can't be coaxed to rev past this point.

I took the filter off and it spits back thru the carb.
Does anyone have any tips what to do next?

Here's a video. You can see my had is wet with gas.
View attachment Stihl 028 spitting back thru carb.MOV

 

[hotshot]

Best guess is that you set the metering lever way too high, pull the carb off & recheck it. It sounds super rich, also check the setting of the H mixture screw. Should be about a turn out CCW from fully seated in.

The second guess is a busted off section of the piston skirt, or it’s simply too worn out to seal off the intake port.

Had he ever ran the saw without an air filter?, or one that had holes where the flocking had fallen off?

 

[mountainlake]

Thats my guess also, worn out piston skirt letting the mix blow back through the carb. Steve

 

[Mad Professor]

Check the spark screen in the muffler. From there I'd suspect carb problems. Needle/seat dirty/not sealing, or metering level.

That is assuming the piston skirt is not overly worn.

 

[Cascadium]

Problem is, it's about 3 hours from me right now - dangit I shoulda brought it home to work on it.

I will take the carb off and peek at the skirt. Yeah thats a reasonable theory why it might chuff out of the carb.
I bet the piston is perfect. Just a guess cuz I don't think it even wore out one saw bar.
I will post pics of the skirt when I can..

Also will check the position of the mixture screws.

Excess exhaust pressure is a feasible cause to puff out of the carburetor.
Yes I will check that. I did not know it had an exhaust screen.

It has a 24"bar on it and was working good for awhile.
Then started too have trouble pulling the chain and seemed to lose power.
I thought it was the long chain but the power continued to lessen.
So the exhaust plugging up is feasible for the lost power and back-pressure too.
Its kinda quiet too, I'm betting the exhaust screen is the problem.

Theres another recent thread regarding an 028 AV Super https://www.arboristsite.com/threads/stihl-028av-super-rebuild.367009/#post-7981965

 

[aokpops]

I would check the flywheel key.

 

[Captain Bruce]

Hi folks,
I have a Stihl 028AV Super that I inherited from my FIL. He said it never let him down.
Well I had to buy a new coil, and rebuild the carb, and change all the hoses.....but I've used it a lot since, and it was working great.
Compression is good, stiff. He was a contractor, not a fire-wood cutter etc, so i don't think it's worn out.
It got stolen too, and the cops brought it back to me. Which made me happy 'cuz I think about him whenever I use his 028.

But trying to use it this season... it won't rev out. It starts & idles OK, but this is full throttle.
It can't be coaxed to rev past this point.

I took the filter off and it spits back thru the carb.
Does anyone have any tips what to do next?

Here's a video. You can see my had is wet with gas.
View attachment 1104179

Its junk. Spare yourself the long-winded emotional history. Its a chainsaw needing a new engine, that isn't worth the cost.

 

[Cascadium]

Its junk. Spare yourself the long-winded emotional history. Its a chainsaw needing a new engine, that isn't worth the cost.

My heart bleeds for you.... having to read that. You poor thing..

 

[Cascadium]

Best guess is that you set the metering lever way too high, pull the carb off & recheck it.

I don't know what the metering lever is.
But, I installed the carb rebuild parts, gas filter and new hoses - and it ran good for awhile, but seemed to be losing power each time I used it.
Like last cut was slower than the first, each use.
And short usage too, like just a few cuts. So then I would try to tune it, adjusting the mixture screws.
But then when it's running that bad the response from mixture screws doesn't tell you much.
So I bet the mixture screws are pretty far off too.

So it doesn't seem like a "metering lever' (if I knew what that was). This was a few years ago.
I haven't used it much, especially after it wasn't satisfying to use.

It does seem like a plugged exhaust screen.
I hope it's that cuz I need it to cut some 24" trees soon!

 

[hotshot]

I don't know what the metering lever is.
.

Tillotson calls it a control lever, it’s critical to adjust it’s height during a rebuild.

Which manufacturer & model of carb do you have? OEM kits are a must.

 

[Mad Professor]

I don't know what the metering lever is.
But, I installed the carb rebuild parts, gas filter and new hoses - and it ran good for awhile, but seemed to be losing power each time I used it.
Like last cut was slower than the first, each use.
And short usage too, like just a few cuts. So then I would try to tune it, adjusting the mixture screws.
But then when it's running that bad the response from mixture screws doesn't tell you much.
So I bet the mixture screws are pretty far off too.

So it doesn't seem like a "metering lever' (if I knew what that was). This was a few years ago.
I haven't used it much, especially after it wasn't satisfying to use.

It does seem like a plugged exhaust screen.
I hope it's that cuz I need it to cut some 24" trees soon!

Take off muffler and post a picture of the piston. Could be the saw is on it's way out. If so and you keep running it will trash the cylinder too.

 

[ZeroJunk]

Make sure the little cotter pin that holds the choke spring is not missing, or the spring that holds the choke flap back is not loose or gone.


Sorry, I was thinking spitting out muffler . Still something to keep in the back of your mind for future reference.

 

[Cascadium]

Take off muffler and post a picture of the piston. Could be the saw is on it's way out. If so and you keep running it will trash the cylinder too.

I will take pics for sure, to keep up the thread.
If the piston is not perfect I probably won't fix the saw.

But the saw is 125 miles away.
I'm gathering info and tips for when I go back to the woods.
Dangit I shoulda brought it back to town to work on it.

 

[Cascadium]

Make sure the little cotter pin that holds the choke spring is not missing, or the spring that holds the choke flap back is not loose or gone.


Sorry, I was thinking spitting out muffler . Still something to keep in the back of your mind for future reference.

Yeah I saw that somewhere, how the choke flap inside the filter can close. I wish it was that simple.
Plugged exhaust screen is my current wish.

 

[Cascadium]

Which manufacturer & model of carb do you have? OEM kits are a must.

carb is OEM.
rebuild kit is from eBay.
I can't remember if rebuild parts are Stihl parts.
Normally I look for OEM whenever possible for critical engine parts. But it was a few years ago.

 

[hotshot]

carb is OEM.
rebuild kit is from eBay.
I can't remember if rebuild parts are Stihl parts.
Normally I look for OEM whenever possible for critical engine parts. But it was a few years ago.

OK. Good luck with the repair, that’s an old school easy saw to troubleshoot & take apart.

 

[mountainlake]

Also check for a clogged exhaust before anything else.. Steve

 

[Vintage Engine Repairs]

Worn intake skirt

 

[leaf]

FWIW, an 028 is fundamentally a pretty good saw. (I have owned and used two over long periods of time. I gave up on one of them, because it was a case split for bearings, and I got distracted and lost patience, but the other one has a relatively recent top end and crank seals - and is a friend.) The only comment I would make is that I regard a 16 inch bar about right for the saw, for balance, for happiness, for rightness of power. 18 ... okay. Longer ... not so much. I convert (without even thinking about it) from spur to rim drive. I use "full chisel" / "high corner" (whatever you want to call it) chain, sharpen with Oregon using "chain tilt." And then, just for personal view, I have a saw that I like and use pretty "hardy" and respect...

 

[Cascadium]

Also check for a clogged exhaust before anything else.. Steve

That’s currently the lowest hanging fruit….and of course the first thing I will check.

I posted this for the hope of low hanging fruit, easy repair…. and was rewarded!!
It’s plausible but its just a theory. If I can just burn a screen…..

I won’t know until I can get back to the saw ~ Aug24