Expected compression numbers for 020AVP

[Mark71gtx]

I am working on one of my Stihl 020 AVP's and it does not want to run well. I pressure and vac tested it and it passed. It has a new coil, new plug, clean filter, new fuel line and filter, and I have tried two different carbs on it, the first is a rebuilt Walbro WA-1 and the second a Tillotson HU-9. Both have similar symptoms. It does not want to idle very well. Saw has electronic ignition. I did a comp test and it is reading 130# with my OTC tester. Piston has no scarring and the rings will push in when I touch them with my screwdriver. I don't think 130 is great, but what should this saw have? Any ideas on why it wouldn't idle? Fuel cap is new as well.

 

[Lone Wolf]

I am working on one of my Stihl 020 AVP's and it does not want to run well. I pressure and vac tested it and it passed. It has a new coil, new plug, clean filter, new fuel line and filter, and I have tried two different carbs on it, the first is a rebuilt Walbro WA-1 and the second a Tillotson HU-9. Both have similar symptoms. It does not want to idle very well. Saw has electronic ignition. I did a comp test and it is reading 130# with my OTC tester. Piston has no scarring and the rings will push in when I touch them with my screwdriver. I don't think 130 is great, but what should this saw have? Any ideas on why it wouldn't idle? Fuel cap is new as well.

130 is low. Are you pulling 12 times or until it stops rising? 145- 150 would be acceptable IMOHO.

 

[Mark71gtx]

I pulled until it stopped rising. Then I pulled it some more... I was thinking 130 was a bit low, but I just wanted clarification from someone else here. I guess a set of Cabers are in my future...

 

[Lone Wolf]

I pulled until it stopped rising. Then I pulled it some more... I was thinking 130 was a bit low, but I just wanted clarification from someone else here. I guess a set of Cabers are in my future...

Replace the whole piston if you can afford to it will make more compression that way. pistons wear out also not just rings. Does the saw hold idle and start easily? Maybe its the carb have you swapped it?

 

[angelo c]

I pulled until it stopped rising. Then I pulled it some more... I was thinking 130 was a bit low, but I just wanted clarification from someone else here. I guess a set of Cabers are in my future...

Might as well replace the piston and new rings as the set is like $10 more then a just set of rings alone.
check prices for both before ordering....(I would pull the jug before ordering either way)

 

[Mark71gtx]

The carb swap was due to poor idling and the proper gasket for the circuit plate not being in the new carb kits for WA/WT carbs. I have reused that gasket. Not sure if it would matter, but I prefer the Tillotson because the kits come with all of the appropriate parts. I can still see the machining marks on the piston. I would assume it was in good shape. There is no telling how long it sat before I got ahold of it. I know it has been on my shelf for several years. The rings are only about $13 for the Cabers shipped.

 

[jmssaws]

Sometimes a set of rings will raise compression but still not fix the saw.
Intake skirt wear will cause idle and spit back trouble.

The bottom of the skirt should be close to bore size.

Most of the time you can see one skirt thinner than the other.

 

[Mark71gtx]

I will certainly check the piston then. These saws only had a mesh air filter. There is no telling how much debris it has ingested in it's time. All of my 020's have the old Stihl logo, so I imagine they are all from the 70's. I just pulled apart a 660 that had a very thin intake side. The filter looked like crap and the element was separated from the top and bottom. Heck of a way to treat such a high dollar saw...