# Stihl O28WB chainsaw running poor



## InstantLegend (Jun 5, 2005)

Hi,

I have a Stihl 028WB chainsaw that will start right up, idles, but when you pull the trigger it speeds up like it should, but runs uneven and lacks power. It almost sounds like it speeds up, slows down, speeds up, slows down type sound. 

I have tried the following list and have had no success in getting it running right. After each step I started it up and tried it.

Adjusted carb high screw
Replaced spark plug
Replaced fuel filter
Replaced air filter
Replaced gas/mix
Removed carburetor, disassembed and cleaned
Adjusted carb high screw again
Checked spark arrestor screen, it was clean
Checked compression, it is very good
Removed muffler and checked exhaust port for carbon build up, it was clean
Cleaned and inspected fuel line, it is fine
Removed carburetor, disassembed and cleaned again
Replaced spark plug again
Put a carburetor kit on the carburetor
Adjusted carb high screw again
Removed carburetor kit, soaked carb in cleaner, and reinstalled carb kit
Adjusted carb high screw again
Replaced carburetor

I don't know what else it could be. 
Please help!

Thanks


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## billsmowers (Mar 21, 2008)

There Is A Air Leak Some Where Posably Around The Carb Mount Presure The System To No More Then 7 Psi And Get Some Soap Solution And Squirt It Around All The Seals And Gaskets F You See Bubbles This Is Where The Leak Is

Hope This Will Help


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## InstantLegend (Jun 5, 2005)

Thanks for the quick reply.

How do I pressure the system?

There is also a second air/vac hose that comes from the crackcase to the carb. I also inspected this hose, although very difficult to get to, and it looks good. Could this hose have anything to do with the problem?


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## billsmowers (Mar 21, 2008)

To Presurise The System Remove The Fuel Line From The Tank Remove The Filter And Conect The Presure At This Point Then Remove The Muffler Get A Piece Of Rubber Th Cover The Muffler Port Then Refit The Muffler Applt The 7psi Presure And See Where It Leaks The Other Hose Is A Breather It Should Have A Duck Bill Valve If I Remember Right Long Time A Way From Saws


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## InstantLegend (Jun 5, 2005)

Won't the air just come out where the air filter connects to the carb?


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## geogrubb (Jul 28, 2006)

With the saw running bad spray carb cleaner along the mating surfaces behind the carb and along the engine block, if the engine tempo changes you have found a leak and can take the proper action. I would also suggest replacing the fuel lines if you haven't done so already. Have a good one. Geo


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## paulr44 (Oct 14, 2008)

geogrubb said:


> With the saw running bad spray carb cleaner along the mating surfaces behind the carb and along the engine block, if the engine tempo changes you have found a leak and can take the proper action. I would also suggest replacing the fuel lines if you haven't done so already. Have a good one. Geo


An 028 is probably at least 10 years old. "Rubber" components dry out, especially if left near lime or fertilizer. I've seen many fuel hoses rot out because of this or old age - don't overlook it.
Stihl saws will change RPM usually when you tip the saw in one direction(nose down or to the right), when it has a crank seal leak, which is what I feel you probably have. FWE seal is the one that usually goes.
The fuel pump impulse line from the CC to the carb. you mentioned is one other area to look.
As Geo says, you have a leak somewhere, finding it is the hard part. With a new carb., it should run gangbusters but doesn't, so the problem is elsewhere.
A local Stihl dealer can pressure-test the crankcase, if they charge you book flat-rate it's 1/2 hr. labor.


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## 30yearTech (Sep 14, 2006)

Many of the older Stihl chainsaws utilized a rubber intake boot, these boots get soft and tear or crack and leak. There fuel pump pulse hose must also be good with no cracks or you will have an air leak into the crankcase and the fuel pump will not work properly. Physically inspect all the rubber components to insure there are no air leaks.


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## InstantLegend (Jun 5, 2005)

How do you get to the rubber intake boot or what do I need to take off to get to it? I can see it, but can't access it to check it for cracks.


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## paulr44 (Oct 14, 2008)

InstantLegend said:


> How do you get to the rubber intake boot or what do I need to take off to get to it? I can see it, but can't access it to check it for cracks.


It's easiest on an 028 is to remove the gas tank / handle assy. You could also pull the cylinder, but that's tough to re-install without special tools and then you'd need a new gasket. The tank/handle assy. is held on via rubber mounts connecting to the crankcase assy. Depending on age, the mounts have plastic plugs in them, and torx screws behind the plugs. You'd have to remove the wrap handle too, and feed the kill wires through as you pull the tank. You also have to remove the metal ring inside the face of the "boot" and kind of nudge the lip through with a blunt screwdriver or similar tool. It sounds hard, but having done them a lot I can tell you it saves a lot of aggrevation trying to fit your fingers into that cramped area.
Of course, you'd have to have the carb. off first too.


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## InstantLegend (Jun 5, 2005)

I finally got a hand pump and pressure tested this saw. There isn't a vacuum leak. I pumped it up to 7 psi and let it sit. A hour later it hadn't changed at all. Now what should I try? What else could it be? Please help.


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## Friggs (Dec 10, 2008)

Try this...
Sometimes the fuel line where it connects to the carb is slightly loose and air is sucked in along with fuel, this will make your saw run like crap.

Friggs


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## paulr44 (Oct 14, 2008)

InstantLegend said:


> I finally got a hand pump and pressure tested this saw. There isn't a vacuum leak. I pumped it up to 7 psi and let it sit. A hour later it hadn't changed at all. Now what should I try? What else could it be? Please help.


I trust you tested both pressure and vacuum - the crankcase must seal in both directions. Are there any physical symptoms, like excessive spit-back from the carb. while running at full throttle? This would indicate a worn piston skirt.
Also - if this has points and condensor, believe or not ignition can create fuel-like symptoms such as slowing down, surging etc. Homelite's 150 was known for that, and I've seen it on other units too.


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## InstantLegend (Jun 5, 2005)

I only pressure tested it. If there was a leak wouldn't it show from a pressure or vacuum test? There is no spit-back or anything like that.

What is the piston skirt? I did a compression test and the compression is 140 psi.

I just put it back together today. I replaced the pulse line because it didn't fit tight on the carb, but unfortunately it still won't run right. I'll take a look at the fuel line.

I just got new points and condensor and am planning to try that next. I don't think the points have ever been replaced. Anyone know of a way to get the flywheel off without a Stihl puller?


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## dennisg (Mar 4, 2009)

I Had A Saw That Did This All I Did Was Replaced Fuel Line Inside The Tank & It Worked.


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## Pudgie (Jan 22, 2009)

To get the flywheel off, Back the nut off but don't remove all the way. using a brass or lead punch and a hammer, smack the end of the crank shaft sharply and the flywheel will come loose. Don't try a gear puller, you will bend or break the flywheel


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## InstantLegend (Jun 5, 2005)

I finally solved the problem with this saw today. I replaced the condensor and it runs as good as new.


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