Stihl 028 AV wont stay running

[psquared]

Stihl 028 AV

I am working on a neighbor’s 028 AV. It was running poorly and appeared to have fuel system problems. There was a lot of fine saw dust in the fuel tank When I disassembled the carb, I found a piece of foam gas filter on the end of one of the needle valves.

I cleaned and flushed the fuel system including tank vent and fuel line. Replaced gas filter, disassembled and soaked carb in cleaner, reassembled set at factory settings and started it with with fresh gas. The saw runs but as time passes it seems to starve for fuel and stall after 30-40 seconds.

The standard adjustments don’t seem to be working. I did not replace any carb components since they all looked to be in good shape. The screen is clean.The tank vent was plugged but is working now.


Any ideas would be appreciated.

 

[Mad Professor]

Carefully check fuel/impulse lines for cracks/leaks, sometimes you need to bend the lines to see them. From there intake boot and it's connection from carb to cyl.

If all this checks out could be crank seal if pis/cyl is in good shape.

Some bad ignitions fail when hot too. When it dies see if you still have good spark.

 

[jeeptj19992001]

did you remove the welch plugs?

 

[psquared]

did you remove the welch plugs?

No

 

[jeeptj19992001]

then you did not completly clean the carb, and those thing are a ##### to replace

 

[psquared]

then you did not completly clean the carb, and those thing are a ##### to replace

I have rebuilt several carbs without removing welch plugs, all with good results.

I think that others have recommended avoiding removal. I'll have to research it.
If there is more debris in the carb, that could explain my poor results.

Any additional input would be helpful.(welch plug removal) I'll check the things Mad Professor suggested also.

 

[jeeptj19992001]

I have rebuilt several carbs without removing welch plugs, all with good results.

I think that others have recommended avoiding removal. I'll have to research it.
If there is more debris in the carb, that could explain my poor results.

Any additional input would be helpful.(welch plug removal) I'll check the things Mad Professor suggested also.

had he same problem it came down to replacing those dame plugs, pulled them there was crap in there, put the new plugs in, they would not seal correctly, so i got a professional rebuilt carb and it did the trick.

 

[NDtreehugger]

The trick there is to keep the edges of the plug and the hole smooooooth

 

[Fish]

Did you remove the lever/spring/needle? Remove it again and hold the carb
up to a light, look through the passage. Then blow it out, look again.....
The screen on the fuel pump side will probably stay, but make sure you can
see light through that passage. The fuel filter breakup clogs up all of the passages. But, I would do this first, before messing with the welch plugs.
A lot of potential problems there....

 

[Rookie1]

Fish you are always talking about blowing.

 

[Mike Van]

I'd have put a kit in that carb - Those diaphrams may look o.k., but they do lose their elastisity, and if carb. cleaner gets on them they seem to shrivel up.

 

[psquared]

had he same problem it came down to replacing those dame plugs, pulled them there was crap in there, put the new plugs in, they would not seal correctly, so i got a professional rebuilt carb and it did the trick.

I had a professional work on 2 carbs for me. After about $70 he gave my saw back "fixed." When I showed him how it wouldn't cut without the choke half closed, he told me I needed a new carb. It turns out that he hadn't cleaned or replaced one of the screens in the carb. I soaked the carb a day or 2 reassembled it (he did put a kit in it, or at least part of one) and it ran fine.

The second carb he cleaned, (no kit available), he advised me to get a new carb. I later soaked that carb in cleaner and reassembled it and it ran fine.

Sometimes a newbie with ingenuity and determination gets past where an unmotivated "pro" leaves off.

Did you remove the lever/spring/needle? Remove it again and hold the carb
up to a light, look through the passage. Then blow it out, look again.....
The screen on the fuel pump side will probably stay, but make sure you can
see light through that passage. The fuel filter breakup clogs up all of the passages. But, I would do this first, before messing with the welch plugs.
A lot of potential problems there....

I did, but I'll do so again and look for more debris

If an additional attempt to clean it out doesn't work I'll pick up a kit and go the welch plug removal route to be sure I get it clean. I found another thread that detailed the disintegrating filter on another 028.

Thanks for the tips, I'll let you all know how I make out.

 

[psquared]

Stihl 028AV runs now

I pulled the carb apart again, including welch plug, soaked it in cleaner again blew it out and reassembled it.

It runs fine now but as the owner's manual says, is very sensitive to minor needle valve adjustment changes. Each adjustment seemed to require a balancing adjustment on the other needle valve or idle screw to maintain acceleration, idle speed, and power in the cut.

The welch plug removal seemed to make the difference thanks NDtreehugger for the diagram.

Thanks for the tips guys they all helped.


You guys are great! :yourock:

 

[pioneerguy600]

I pulled the carb apart again, including welch plug, soaked it in cleaner again blew it out and reassembled it.

It runs fine now but as the owner's manual says, is very sensitive to minor needle valve adjustment changes. Each adjustment seemed to require a balancing adjustment on the other needle valve or idle screw to maintain acceleration, idle speed, and power in the cut.

The welch plug removal seemed to make the difference thanks NDtreehugger for the diagram.

Thanks for the tips guys they all helped.


You guys are great! :yourock:

Now that is what a real carb rebuild is about, I have never come across a carb that could not be rebuilt ,even when a saw comes in to me with the owner saying the dealer/ service center had told him he needed a new carb, that carb would work fine after I did a thorough cleaning and replace all components with a full rebuild kit. A thorough cleaning is not spraying carb cleaner into the orifices and blowing it off with compressed air, it works sometimes but leaves a lot to be desired. IMO
Pioneerguy600

 

[Mad Professor]

Now that is what a real carb rebuild is about, I have never come across a carb that could not be rebuilt ,even when a saw comes in to me with the owner saying the dealer/ service center had told him he needed a new carb, that carb would work fine after I did a thorough cleaning and replace all components with a full rebuild kit. A thorough cleaning is not spraying carb cleaner into the orifices and blowing it off with compressed air, it works sometimes but leaves a lot to be desired. IMO
Pioneerguy600

I agree, unless a Gorilla seated the hi/lo screws..........:censored:

 

[pioneerguy600]

I agree, unless a Gorilla seated the hi/lo screws..........:censored:

I agree somewhat on that point but I have worked carbs that required me to use both hands on the screwdriver to remove the overseated mix screws and replaced the needle screws with new ones and even that carb works a 1 even to this day. I have even removed broken off screws and the carb worked properly after a rebuild. Guess that I have been lucky , did my first rebuild at 15 years old and by now have done many hundred, over 35 years working on all types of engines, two and four stroke.
Pioneerguy600

 

[Scandy14]

Now that is what a real carb rebuild is about, I have never come across a carb that could not be rebuilt ,even when a saw comes in to me with the owner saying the dealer/ service center had told him he needed a new carb, that carb would work fine after I did a thorough cleaning and replace all components with a full rebuild kit. A thorough cleaning is not spraying carb cleaner into the orifices and blowing it off with compressed air, it works sometimes but leaves a lot to be desired. IMO

+1 I agree as well. I just rebult a carb on an 024 that a local shop said needed to be replaced. I put a kit in it and after the kit did not cure the problem, I removed the welch plug, cleaned it again, reassembled and the saw works great now. It was the first welch plug I had ever removed and was not too difficult.

 

[Dale]

I know I'm resurrecting an old thread here, but I have the same symptoms. Question, where does the "welch plug" shown on the 1st page reside on the carb ? Pretty sure my carb is a Walbro if memory serves. Is it on the body ?

 

[psquared]

They are on the carb body, but all carbs don't have them. If you get the make and model # detailed parts lists are available on line.