Stihl 020AV Super compression

[CTPhil]

I'm trying to figure out what's wrong with my Stihl 020AV Super.

About 3 years ago it became harder to start, and when it got fully warmed up (5-10 minutes of use) it would stall out. I repeatedly tried carb adjustment, it helped a little, but not enough.

I finally gave up and took it to the local dealer/hardware store for repair. They said it had no spark (it did) and replaced the coil and plug. They also put a carb kit in. $150 later I got it back and it doesn't run any better. It seems to me that they just repalced some parts and hoped for the best.

So I'm going to spend the time to get it right myself.

I started with a compression test, 115 lbs. Is that too low? I see saws on Ebay talking about 140-150 lbs. compression. The cylinder/piston looks fine from what I can see with the muffler off.

I'll start there, and work up from that. One other thing worth mentioning is that when using the saw, I need to regularly crack the gas cap to keep it running.

Thanks in advance.

 

[PES+]

It appears that you have low compression. Even with a less than optimum compression gauge it should show more than 115....you may have stuck rings or the rings may be worn out. The needing to crack the gas cap to keep it running is an indicator of a blocked tank vent which can over time cause lean running and engine damage. If you are up to disassembling the saw there are plenty here to help you fix it....if not find another dealer by calling around and ask how much they would charge for a crankcase pressure/vacuum test and a compression test. I doubt the hardware store even knew how to check compression properly and I would not return there for service.

First I need to remember where the vent is

 

[PES+]

Does your fuel cap have an air bleed hole in it?

 

[CTPhil]

Does your fuel cap have an air bleed hole in it?

My fuel cap has a small screw in it, I took it out but couldn't see what the function of it was. I did the compression test with an automotive screw-in tester, so I think the reading is reasonably in the ballpark. I've already got as much unfruitful labor expense as I'm willing to stand into the saw, so from here on out it's all me, for better or worse.

Thanks for the quick reply!

 

[PES+]

Oye.....

Most likely someone put the screw in the cap to stop the vent from leaking....it should not have the screw.

Does yours have the removable recoil? The early 020s did not

 

[CTPhil]

Most likely someone put the screw in the cap to stop the vent from leaking....it should not have the screw.

The cap came with the screw in it, it is threaded into a metal pin that is cast into the plastic.

Does yours have the removable recoil? The early 020s did not

I believe that it does.

 

[Lakeside53]

Does your compression tester have the schrader valve at the screw-in tip?. If not, it will read very low...

 

[CTPhil]

Does your compression tester have the schrader valve at the screw-in tip?. If not, it will read very low...

I don't think it does, if I understand what a schrader valve is. It has a pressure release valve like a tire valve on a block just under the dial.

 

[Lakeside53]

In that case, your reading is not valid. You need a valve at the tip (most also have a release valve just below the meter - the volume of the tube is being added to the compressed cylinder volume...

 

[CTPhil]

Do you have any recommendations for a tester?

 

[Lakeside53]

Do a quick search on AS for "compression testers". This problem comes up every few weeks - about half of the testers in stores are correct... Mine is just a no-name local autopart store tester. If you can see the valve in the tip and it has no adapter for the chainsaw thread, it will work fine.

 

[CTPhil]

Thanks! I guess I'd better get that sorted out before going further.

 

[Lakeside53]

Yep.. lot of saw get torn down because of the wrong compresson tester!

I'm an expert... a long time ago I tore down my first 034 because that... oh well...

 

[CTPhil]

I'm most grateful to be able to benefit from your experience,

 

[CTPhil]

Well, I think that I may be back to being screwed. I more closely examined my compression tester, and there seems to be a schrader valve at the end of the hose, where the quick-coupler screws on. So it's not right at the tip, but about 1 1/2 inches up. At any rate the valve is before the hose.

 

[PWB]

I don't think it does, if I understand what a schrader valve is. It has a pressure release valve like a tire valve on a block just under the dial.

Chances are there's a shrader valve in it somewhere then. Looks just like a tire valve somewhere farther down between the sparkplug hole and the guage. If the pressure stays up after it builds, there's a valve in it somewhere. Crank the thing over until the pressure stops building, even if it's a dozen pulls.

 

[Ax-man]

I don't know if anyone has ever posted a picture of quote " the proper compression tester " here is mine, it is a deluxe automotive type but has the valve in the bottom of the hose and a valve at the bottom of the gauge.

Good compression on an 020, 150 lbs, doesn't matter weather it is a super or not, much less than that your wasting your time on it trying to get it to run. If the saw does start and run the compression is probaly OK.

CT, change out your fuel line for starters, it makes a difference in these saws because the inlet to the carb from that goofy flange the carb is mounted onto has to mate to the fuel line in the tank, a bad or not so perfect seal in this area will make them hard to start, also if the fuel line is extremely soft it can collaspe down resticting fuel flow. It is a cheap fix. While the thing is apart check the boot that fits over intake port if isn't on right it too can give you fits.

 

[CTPhil]

Thanks for the pictures. My guage is like that but has an air compressor type quick coupling fitting at the end. The valve is where that fitting screws on. Hard to believe the short distance between the plug hole and that valve could skew the reading so much.

I was planning to change the fuel line, I searched other posts looking for ideas and that was suggested, thanks for the reinforcement. But it sounds like there's no way around biting the bullet and addressing compression. The saw is very hard to start.

 

[treeclimber jul]

Hang on to the starter handle and let the saw drop. If the saw drops fairly easly than it might have low compression.


S.P. not sure if this works with the top handle tree saws

 

[Lakeside53]

Thanks for the pictures. My guage is like that but has an air compressor type quick coupling fitting at the end. The valve is where that fitting screws on. Hard to believe the short distance between the plug hole and that valve could skew the reading so much.

I was planning to change the fuel line, I searched other posts looking for ideas and that was suggested, thanks for the reinforcement. But it sounds like there's no way around biting the bullet and addressing compression. The saw is very hard to start.

Think of it this way (and I'm making up the numbers so the math is easy...)... If you have a compressed cylinder volume of 6cc, and you add 2 cc's of hose or coupling before the schrader valve, then your reading will be 33% low.. or is it 25%? but whatever, you get the idea..