Stihl O-28-AV what to try next?

[sanmigmike]

It was running fine and then it slowed a few times and stopped. New spark plug, new air filter, new fuel line (old one was rotted) seem to be getting spark, air, fuel and when I hold my finger in the spark plug hole I get some compression. Thinking of putting my compression gauge on it, any idea on what I should see? Any ideas on what to try next? I got wood to cut and beer to drink, and I have to cut the wood first!!

New here, so if this is in the wrong place and all that I am sorry, did try to look at old threads as well....

 

[retoocs555]

If you've got a compression gauge try it. Hopefully you'll see at least 110 psi or so. 160 would be better.

 

[Wood Butcher]

Have you tried getting it to fire by giving it a 2 second spray of WD40? Or if you get desperate 2 seconds of WD40 and 1 second of starting fluid.

Remove the muffler and look inside, can you see scoring at all?

 

[Lakeside53]

Have you tried getting it to fire by giving it a 2 second spray of WD40? Or if you get desperate 2 seconds of WD40 and 1 second of starting fluid.

Remove the muffler and look inside, can you see scoring at all?

Just use your fuel mix. WD40 worked fine until they changed the formula a couple of years ago and now propel it with Carbon Dioxide...

If it fires and runs for a few seconds, it's likely your carb or impulse line.

 

[Wood Butcher]

My favorite way of applying 2 stroke fuel is with an oil squirt can, that way you can use it as a penetrating oil too, albeit a somewhat flamable one. Also, with a can you can keep squirting it to keep a motor running. Sometimes that helps with a gummed up carburetor, if something has sat for a few years with gas in it you can get it started and keep it running for a few minutes to see if it can work the varnish out of the carb.

 

[Sprig]

Agree with Lakeside, had a similar prob not too long ago, turned out to be carp (slag-like build up) blocking the teeny hole in the float bowl where it enters the maze into the carb throat. (don't even know if you have one on yours lol), seems you have done most of the elimination already, I'd start by pulling the H/L needle valves and cleaning them before anything else, use that losable red straw that (supposedly) comes with the WD and give em both a short blast too (the holes I mean), I stand to be corrected. Have a feeling it is simple as maybe a small blob of the old line getting in there but I am far from a pro, just gut reaction.
My 0.02$ worthlessness

 

[Fish]

Remove the muffler cover and look at the piston, that will likely tell you a
lot. The foam insert on the fuel filters break up with age, and the remains
stay in the carb screen like a small pinch of snuff, so going through the carb
would be a good idea, but like I said, look at the piston first.

 

[sanmigmike]

What an exercise in MY stupidity, got the compression checked.

Got the compression check done, seems to indicate about 50 psi.!!

Looking through the plug hole the head of the piston has a fine even layer of carbon and not sure but think I might see some scoring or a funny wear pattern around the ports on the other side. Assume tearing it down next?

Given the price of Stihl parts how far do you have to get into rebuilding one of these before it is cheaper to buy a new one?

Have a GRIP brand compression tester that never did work quite right. The hose from the gauge is supposed to have a fitting like a female quick connect fitting on an airhose. Never did fit right. Never could find an address for GRIP to complain about it. Bought a fitting and a new female fitting now works okay. Should learn to stay with decent (name brand?) tools!

Thanks for all the help so far!!

 

[THALL10326]

Got the compression check done, seems to indicate about 50 psi.!!

Looking through the plug hole the head of the piston has a fine even layer of carbon and not sure but think I might see some scoring or a funny wear pattern around the ports on the other side. Assume tearing it down next?

Given the price of Stihl parts how far do you have to get into rebuilding one of these before it is cheaper to buy a new one?

Have a GRIP brand compression tester that never did work quite right. The hose from the gauge is supposed to have a fitting like a female quick connect fitting on an airhose. Never did fit right. Never could find an address for GRIP to complain about it. Bought a fitting and a new female fitting now works okay. Should learn to stay with decent (name brand?) tools!

Thanks for all the help so far!!

50LBS of compression,yikes, she tant gonna run. Yank that muffler off and you will see whats wrong. Jug/piston run around 200-250 depending what area your in. Worth fixing, hmmm, yep. A new saw of that size will run over 400.00....

 

[Finnbear]

028 pistin/cyl sources

These are on evilBay right now
Item number: 7756675744 (new)
Item number: 7756192772 (used)
Item number: 7756409839 (new/used)
Item number: 7756409839 (new)

Another source for new aftermarket parts-whole set $120
http://www.mfgsupply.com/m/c/44105.html?id=yvkHBo7y

If you don't want to fix it you might think about selling it to me.

Finnbear

 

[GASoline71]

Get a second opinion on that compression test, 'cause it doesn't sound like you are too sure of the one you did. Also check the impulse line like Andy said. Impulse lines are always overlooked and can usually be the culprit. Good luck

Gary

 

[sanmigmike]

Tried squirting fuel and starting fluid in it and

it doesn't even show an interest in starting. I have doubt about the exact number on the compression test but I am sure it is in that area. Tends to indicate a little high when I last used it on a car (the number I got was great for a new engine and a bit high for one with 200,000 miles but possible?) but it shows the same value when you repeat the test.

Going to rebuild it as soon as I have the time to take it apart, might use evil-bay for the parts or go the aftermarket way.

Is the MS 280 Q-CS the current replacement for it? Thinking of something just a touch bigger since I have a small Homelite that is running well, or was the last time I used it.

Cleaning up slash and a lot of stumps on eight acres, stumps about 36 in. in dia. and cutting up the waste logs for firewood. Open to other brands aside from Stihl but tend to buy stuff that will last a few years when I can afford it.

Thanks for all the help so far.

 

[Freakingstang]

if that compression gauge is an automotive gauge, it probably doesn't have a check valve, so that 50psi might be 100 or 150.... Look at the inside of the hose and see if it has a valve

 

[Allan.K]

Yes rebuild it..The 028 is a heck of good saw..I had one for many years..Never had to rebuild it tho..Stay with factory parts (Stihl)...Don't use aftermarket ones they don't hold up as long as Stihl replacements...Or trade it in on a MS260 I think that is what repalced the 028 not for sure tho..


Allan

 

[sanmigmike]

Has a schrader type valve on the tube and one on a block below

the gauge, it goes back to zero each time before I do a test. Good point.

if that compression gauge is an automotive gauge, it probably doesn't have a check valve, so that 50psi might be 100 or 150.... Look at the inside of the hose and see if it has a valve

 

[GASoline71]

I've got an 028AV Wood Boss... trust me dude, one good little saw. Been lucky enuff to not have to do a rebuild yet.. Owned it since 1985.

Try this... take the air filter cover off, and pull the filter. Check the black wire that leads to the Master Control Switch. It can become loose and also get clogged with junk, making a poor connection. If it grounds out, the saw will not start or sometimes sputter and die. There is a small screw that holds the rod of the Master control switch. Remove it and the switch and then you will notice that the wire rotates on the switch in a brass "housing". Give it a shot of electrical contact cleaner to get any crud out. I had to give mine a small pinch with a pair of needle-nose pliers to make a good contact.

Reinstall the switch (it's a PITA) and give it a crank. The same symptoms happened to me, where I thought it was what you describe. But it ended up being a bad contact from the wire to the switch. Hope this helps. Good luck, because this is a great saw to have.

I'm not sure if i described this very well... maybe Lakeside (Andy) can elaborate.

Gary