Stihl 020AV Super compression

[CTPhil]

I got my compression tester from Bailley's and gave it a go.

Before with my old tester: 110 lbs.

After with new tester: 170 lbs.!

Wow am I ever surprised. I guess it's on to other potential problems. I'll check the fuel system and ignition next.

I don't know what the difference was between testers, whether my old one is bad or the schrader valve is poorly located, but I'm sure glad I went the extra mile before pulling the cylinder off!

 

[Lakeside53]

Damn, another great saw I won't be able to buy cheap! :greenchainsaw:

Glad it all worked out.

 

[CTPhil]

Damn, another great saw I won't be able to buy cheap!

So that's you running up the parts saws prices on ebay?

 

[PES+]

After I took the banana out of my ear I understood what you were saying Andy.

For me I question the 170.
It is possible though pretty unlikely on a stock 020...more like 160 tops after running a couple of days

I'll post a way to calibrate the testers later.....I used to do several things to check pressure gauges and I have to sit and think on it with the gauges in hand.

I still have a whole lot od cheap testers in boxes and I can't find a one that does not have a valve in the end of the hose or in the case of the small push ins the end of the metal tube. I am not at all suprised that Sears would sell such a useless tool as they are just about sales numbers regardless of whether the item works for it's intended purpose or not.

Price point is everything

 

[PES+]

Now back to the original problem.

Can you post a pic of the saw and a pic of the gascap off of the saw Phil?

I am having trouble recalling the layout on the non top handle 20 but I am pretty sure the vent was in the cap.

 

[kd460]

Glad it's not the compression. So, where are you at with the saw? I'm guessing your problem is still not resolved? Sounds like a fuel issue, however, how is the spark? When having trouble with it running, remove spark plug and ground it to the head, give it a couple pulls and look for a nice blue spark, if thats OK, then pretty safe to move on to fuel related problem. But, to be safe, check themagneto and flywheel. They should be clean. If the flywheel has rust on the magnetic portion, clean it with fine grit sandpaper and brake clean. Same with magneto, make sure it is clean of oil and dirt (at the tips near the flywheel).

Probably could stand a rebuild of the carb. A kit is about 5 bucks, rebuild manuals can be downloaded from the internet. Give it a once over with lots of carb cleaner.

Your tank vent has me thinking. Is your saw designed to vent thru the cap or someplace else? I'm thinking someplace else. Need to locate the correct vent and see if it is clear. When was the fuel filter changed? Check the impulse line for a leak? Maybe fuel line has a leak and when tank drops to a certian level it exposes a hole in the fuel line? (just guesing at this point)

When the saw stalls out, remove the fuel cap, listen for any vacume. Try to restart and see if it runs now. That will tell you if it is a venting issue. Same thing with spark, check it after it stalls, sometimes coils or plugs can get flakey after they heat up. Another check would be after it stalls, prime it, then see if it runs.

Other thn that, look for carb or impulse line leaks by spraying wd-40 around the base of the carb, and the impulse line, if the way the saw runs changes when spraying, you found a leak.

Based on info provided, I'm thinking fuel venting problem, or carb needs a once over. Good luck, KD

 

[Ax-man]

Wow, 170 lbs, that does sound high for a stock 020, especially one that has some run time on it. I have one that will put out 165 lbs but it has had the engine altered.

The venting on an 020 is through the cap, either through a small hole in the top of the cap or through a small screw in the side of the cap, a Super will have the screw in the cap.

In addition to all the other pointers you have recieved, you might want to check the clutch side bearing to see if it is bad, no play in the bearing, if the bearing is bad it is almost certain the seal is leaking that could be a cause of hard starting. The clutch, sprocket and preferable the oil pump cover and the oiler gears must be removed. If you have never taken a clutch off they have a left handed thread, clutch removal is a whole different subject in itself.

 

[CTPhil]

Can you post a pic of the saw and a pic of the gascap off of the saw Phil?

I am having trouble recalling the layout on the non top handle 20 but I am pretty sure the vent was in the cap.

The saw:

Detail of the cap:

I'll start to look into the suggestions everyone's made. Fuel line problems make sense, I'll go over that. A couple of weeks ago I did check the spark, I think it's a little iffy, it was yellow/orange, not blue.

I ordered up a parts book, so as soon as I get that, I should be good to dig further in.

 

[PES+]

The vent is in the cap on that one.....you need another cap with a working vent. Maybe an Oregon dealer can get an aftermarket cap for low dollar.......ask Uwharrie

 

[CTPhil]

I did get another cap. For the life of me I can't figure out how that screw in the cap has anything to do with venting.

 

[Lakeside53]

The gap in the threads allows air to pass into the tanlk, but somewhat stops the gas from pouring out...

 

[Lakeside53]

I'll start to look into the suggestions everyone's made. Fuel line problems make sense, I'll go over that. A couple of weeks ago I did check the spark, I think it's a little iffy, it was yellow/orange, not blue.

I ordered up a parts book, so as soon as I get that, I should be good to dig further in.

Check your spark by bending up the grounding electrode - the large gap simulates the conditions in a cylinder where the pressure requries a much larger voltage to jump the spark gap.

 

[CTPhil]

Check your spark by bending up the grounding electrode - the large gap simulates the conditions in a cylinder where the pressure requries a much larger voltage to jump the spark gap.

What would I then be looking for?

Also, back to the gas cap, if the venting is through the threads on the screw, what would change to make it not vent?

 

[Ax-man]

What would I then be looking for?

Also, back to the gas cap, if the venting is through the threads on the screw, what would change to make it not vent?

Same thing a blue spark, if it doesn't jump a wide gap you have problems. With an inline adjustable spark tester a good ignition will jump almost a 1/4" gap, now that is a wide gap. You can have spark in a saw but it might not be hot enough, takes a certain voltage to ignite the air fuel mixture. You might be able to cheat a little and make the plug gap tighter like down to 10 to 15 thousands.

Dirt, dust and just plain old age, seldom is venting a problem but it does happen. Venting is a hard problem to diagnose unless you have a pressure and vaccumm tester which means another tool to buy, Maybe Lake has a way to do this without buying a tool. I can think of a way but it is not cool.

 

[kd460]

What about removing the vent screw, try to get some type of a tube in the hole (where the screw would go), run the tube up so fuel does not leak out and see what happens.

I'm not sure about that model of saw, but, does it leak fuel if say you have 1/2 a tank and you leave the cap a little loose?

After the saw dies, will it restart once you open the cap and reclose it? (equalize the pressure). KD

 

[CTPhil]

Same thing a blue spark, if it doesn't jump a wide gap you have problems. With an inline adjustable spark tester a good ignition will jump almost a 1/4" gap, now that is a wide gap. You can have spark in a saw but it might not be hot enough, takes a certain voltage to ignite the air fuel mixture.

Maybe that's why it's so hard to start.

I'm not sure about that model of saw, but, does it leak fuel if say you have 1/2 a tank and you leave the cap a little loose?

I haven't tried that.

After the saw dies, will it restart once you open the cap and reclose it? (equalize the pressure). KD

It did, but it's so hard to start now, I need to fix something before trying again. When it wasn't quite so bad, I actually used it by cracking the cap on the fly when the engine started to falter.