Help... Stihl 028 AV Super

[Dale]

Just found the site and have been browsing around, you all seem to be extremely knowledgable and rabid chainsaw fanatics. Boy can I use some help with my 028 Super.

A little background. I'm a weekend warrior, and probably only cut 2-3 cords per year, but I am very careful and courteous when it comes to TLC for my saw. I bought the saw used for $170 in 1991 and boy do I LOVE IT. Well my pullcord broke, so I buy a new one, and notice the tension spring (for the pullcord) is a bit rusted and worn so I replace it also. Now mind you, up until this point the saw has been running like a top (for 14 years now). Well I yank on the new cord and after a bit longer than normal, it starts, runs for 10 seconds or so, and dies out. I choke it, throw it on start and it does the same thing, runs a bit then dies out. OK, I figure it's been a while since I cleaned the carb, so I get a kit and redo it (gaskets, needle, spring), I also replaced the fuel hose as it had some wear cracks, and fuel filter. Fille er up with gas and SAME THING. Now I was told to close noth the H and L screws on the carb, and then back them off 1 full turn. I did that, and it won't start at all now. I've seen mention of some kind of ignition coil, could this be a problem ? Oh, I also replaced the spark plug. I may try to mix a new batch of fuel since it may be "bad" for some reason, but I really doubt that is it. Well do you fellas have any suggestions ????? I am really frustrated, and I just love this saw to death.... it's always been one heck of a dependable worker for me. Thank you.

 

[Dale]

Oh forgot to mention. The dealer sold me a new cloth type air filter, as mine was what he called "outdated" being the original mesh screen type.

 

[Grande Dog]

Did you change the plug before or after the starting problem? I've run into a few bad new plugs over the years.

Grande Dog
Master Mechanic
Discount Arborist Equipment and Tree Care Supplies

 

[Dale]

After Grande. I figured it would be a cheap $2 fix if indeed it was the problem, but no such luck. What baffles me is that it ran fine up until the pullcord snapped, no tampering at all with carbeuration. Well the next "cheapest" step is to get a new mix of gas and try it. A dealer said do a compression test, but the saw did not just die while I was cutting, which if it did, I would think it may have blown up, and would be worthy of doing a compression test. Besides, this is the only saw I have, it's not my living, and I don't want to spend $$$ just for a compression gauge that I'll use one time.
While we are on the subject, what is an acceptable range on the compression test, just in case I take it to have it done ? Thanks.

 

[Mange]

I would squirt some fuel, or ether in it and see if anything happens, if it does then there is hope.

 

[Lawn Masters]

It sounds like it may be an air leak, quite possibly. does the engine idle slightly faster than normal when you start it? if it does, then an air leak is a very likely source of your troubles.

 

[Dale]

oldsaw,
it doesn't stay running long enough to actually idle, so I'm not sure, but... tell me more about an airleak. Where might I look for the "leak", keeping in mind that I changed the fuel line, fuel filter, carb gaskets (yes the carb is tightened down very secure). Could it be on the muffler side of things ?

You fellas don't seem to be leaning towards the ignition coil, which I had suspicion about. Thanks for all the replies so far.

 

[Lawn Masters]

The air leak is most commonly a crankshaft seal leaking, which can be tested by spraying wd40, or ether around the seal, and turning the saw over by hand, if it isnt leaking you will see nothing, if it is, there will be bubbles forming where it is leaking. on a second thought, have you also replaced the fuel filter in the tank?

 

[DirtTroll]

If it's dying out after you just after start it, then I seriously doubt it's the electronic ignition. That makes it a fuel issue.

Sounds like a worn out diaphram. Or missing spring behind the diaphram. Did u forget to put in the spring behind the diaphram. I've done that before and gotten the symptoms you are describing.

The next thing I would check would be the impluse line. A cracked impulse line will not actuate the diaphram enough and will cause it to die out. You said you replaced the fuel line, but I doubt you replaced the impulse line. I've had more issues with impulse lines than fuel line, but thats just my experience.

I rarely bother with the needle valve. I have never seen one go bad. Typically the saw will totally sh*t the bed before you will have a problem with them. The needle valve just keeps the saw from flooding and thats not your issue anyway. You aren't getting enough fuel.

 

[stihltech]

028

replace the pulse hose from the carburetor to the case, below the cykinder.

 

[Mange]

Do you know if there is spark more than one pull. I still think the ether test is good, if you get it to run 2-3 times with ether there is good chance the coil is good. You can have spark a while with a bad coil. But after what you write, I go with fuel system. Squirt some gas down the throat of it, or spray with ether, that way you will not have too think about many things at the time. You can not check everything at once and have to start some where.....

Has it been stored cold? I do not know your climate, but here is a common problem with Firewood-saws at winter: Ice plugs!!! The saw is not operated regularly and there get condense in tank, then freeze in the tubes or carb. I had one today. He let it get worm then it fierd up like usual.

 

[Dale]

Guys your suggestions are great.

Mange... No ice problem, but I will try the ether and see what happens.

Oldsaw... Yes I replaced fuel line and filter. Question, where do I spray the
WD-40 and check for bubbles, what do I have to have removed in order
to do this ?

DirtTroll and Stihltech.... what is this pulse or impulse line that you speak of.
Exactly where do I find this ? Does it somehow carry fuel ?

Fellas pardon the ignorance, but I am just a basic guy. I don't get too deep into maintenance, but I am fairly smart.

The reason I was mentioning coil is that I have a farm tractor (Ford) that would conk out after 15-20 minutes or so due to bad coil. Let it cool down and bingo, run it for another 20 min.

 

[coyote556]

the impulse line comes from the crankcase, below the intake, and feedes positive/negitive pressure to the carb, to make the diaphraghms pump fuel.

 

[DirtTroll]

The impulse line takes the air pressure from the down-stroke of the cylinder to pulse the diaphram and the spring pushes it back. The oppisite side you will have the (for lack of a better term) the rubber/plastic checkvalve. This pumps the fuel from the tank to the carburator. This line runs from the diaphram side of the carburator to the bottom of the cylinder.

Electronic ignitions typically work or don't. The older style points/condenser system have diaelectric condensers as they aged (dried out, the dielectric is oil wrapped paper) the spark would get weaker.

 

[Mange]

Electronic ignitions typically work or don't. The older style points/condenser system have diaelectric condensers as they aged (dried out, the dielectric is oil wrapped paper) the spark would get weaker.

There is a number of things that happens to new style ignition systems.
I have seen many that has been too hot, and after a pull or two they short circuit them self. Another thing that is common is cracks that allows water to enter.
When I change a coil I try and figure out what happened, many of them are cooked. And the coil is a common problem on all models and brands.

Rule out one system at the time, to begin with, not one component at the time. Checking every part is timeconsuming and confusing.

 

[TonyM]

Did you put the new carb kit gaskets and and diaphragms back in the right order. I just put together an 028 carb I had apart several times, and mistakingly put the metering diaphragm on the carb first, and then the gasket. It is supposed to go gasket first. The saw would fire and die, and the I could crank until my arm fell off, but it was simply flooding out. On the other side, the fuel pump diaphragm goes first, then the gasket. Just the opposite. Also, did you change the welch plug, and if so, are you sure it is sealed. If it is not sealed the idle circuit will not work correctly, as the low speed needle is by-passed by the leak. Do you have a tilloston HU carb? I down loaded the service manual from the tilloston website, and it was quite helpful. I just fixed a very stubborn 028 that ended up having a bad crank seal, non working choke, air leak at the carb, plugged low speed carb adjustment, and leaking welch plug. Talk about a pain to troubleshoot!

 

[Al Smith]

It's a fuel thing

First of all,check the impulse line.Secondly,check the setting of the fuel shut off lever[connects to the shut off valve],should be flush with the body.Set too high,and it will flood,too low,and it will die for lack of fuel,this is critical.It most likely has a Tillotson Hu,or Walbro Wt carb.Both have excellent web sites,for info.

 

[stihltech]

hose

Two things I find bad on over half the 028s I repair, fuel and pulse hoses. Replace the pulse hose.

 

[Dale]

Phew !!! you fellas have been at this a while. I'm not relating the terms you all speak of to the part on the saw. Since I bought the saw used, It didn't come with a service or parts manual, but I do have one on order. Here's where I'm at:

-- it's not "bad" fuel, as I made up a new batch (I still run 40:1).
-- it's probably not electrical as I had great spark to the plug.
-- I'm very confident the diaphragm and gaskets went on correctly on the
carb. tune-up, as I marked them as they came off. This must be a mini
tune-up kit as they only supplied gaskets, diaphragm, 1 needle and the
clip for it, and screen. I was expecting to change needles for the H an L
adjustments, but they didn't supply them.
-- This impulse or pulse line you speak of, I'm still not getting where it's at.
By the sounds of it it's not in the carb. Someone said "crankcase". Now
there is a small hose that fits over what looks like a plastic breather that
comes out of the gas tank itself. The hose is about 2" long and attaches
over said nipple, and just vents out of a hole. I'm assuming it is merely a
vent, am I wrong ? The hose does have what looks like 2 small spring
inside it... why I don't know. Ayhow, EXACTLY where do I look to locate
this pulse line... what needs to be removed to find it ?
-- Someone spoke of a fuel shutoff valve. Where the beejabbers is that ?
I'm used to seeing petcocks on various machines, but I didn't see one on
this. Like I said, I had the carb completely off, and there was a fuel inlet
stem, and an exhaust port, and that's it. So, EXACTLY where do I look to
locate this fuel shutoff valve... what needs to be removed to find it ?

I'm leaning towards this pulse line IF I CAN FIND IT... Or maybe a "stuck" High Low needle. Like I said I must've bought the GENERIC kit since it didn't contain needles for the H and L.

Oh, I had the muffler off to inspect the piston and rings (looked ok, not seized). I used the old gasket when putting Muffler back on. Is that OK ?

Also, is it routine maintenance to replace piston rings, I know Motocross racers replace them after every race. Don' know the schedle for a saw.

Well guys thanks a bunch. I would really appreciate you fellas picking out the questions I asked and giving me specific answers (hand-holding...LOL).

Oh fwiw... my carb is a WALBRO 16A.

.

 

[TonyM]

There are two nipples on the carburetor. The fuel line hooks to one. The other nipple faces straight towards the cylinder, parallel to the carb mount bolts. As you slide the carb onto the bolts, this nipple engages the impulse hose. It is located near bottom of the carb towards the right side of the saw. The hose fits tightly into a hole in the wall between the carb and the cylinder. I took the handle off from the saw when I changed it. It might be a good idea to remove the handle anyway, so you can inspect the rubber boot between the carb and cylinder for cracks or holes. Good luck.