HELP! Stihl 076 AV Super- Bogs and Dies When Hot

[Steck]

Hey guys. I have an 076 AV Super that has been a fantastic saw the last couple of years. I use it primarily for milling but it gets used for really big firewood stuff now and then. I was finishing up a job today so last night I did the usual prep, sharpened the chain, etc and it ran fine. I only ran it a few seconds just wanted to make sure it would start and it fired right up. Today I got about 2/3 through my first slab and it started acting up. It bogged down and would bog or shut off if I tried to give it throttle off idle. I was also really concerned because there was white smoke coming from the fan/electrical side. I knew the saw wasn’t running lean or hot so that it would cause that. I changed the plug and let it cool down. I finished the pass and started another one, saw was running well. But it wasn’t long before it did the same thing. Bogged down and wouldn’t come off idle. This time it was done. I can get it to idle but that’s about it. Even after letting it cool off, it runs ok for about 10 seconds and then craps out. I couldn’t finish the cut. One thing I noticed in addition to the hot white smoke coming out the fan side vent, was that the usual RPM governor seemed to be non existent. If you can coax it into running, it would spin free, higher than the usual governed 9-9400 and then it would crap out. So I think I have an electronic ignition issue. Sadly I don’t know much about this governor and electronic ignition system on this saw. What do you guys think it could be? Can I get parts? If I can’t find the exact NOS parts, what will work? I wanted to keep this thing original but I’m open to scrapping the governor system and just doing what will get me back milling asap.

 

[av8or3]

Fuel (lack of it) would be my guess. Since it started and ran, it’s not ignition. There is something causing it to run lean, it may have damaged the saw already, but I would bet on a lean condition being the cause of your pain.

 

[Steck]

When I pulled the plug it was dripping wet. I think it’s actually the opposite. I don’t think it’s a lack of fuel to burn I think the module or coil is bad and not igniting the fuel. When it idles it does ok, when you touch the throttle it wants to die right out and mostly does. I will, however, check the carb and intake to make sure all is well. I’m going to remove the saw from the mill and fire it up. I need to be able to test the ignition while it’s cold (presumably it’s still ok while cold) and test it while hot. I’m hoping it wasn’t running lean and I have now screwed it up. However, I’m not the best with electronics and meters, etc. my dad does well with it, so can anyone tell me how to test the ignition and what to look for? Does anyone with an 041, 075, 076 type saw have any input on this ignition and governor system on these saws?

 

[Al Smith]

I've only seen two of this model in my life time and never worked on one .That said according to the IPL it uses a trigger plate to control the coil .That part number is 1118-400-1004 and rather costly if you can even find one .However it might be replaced using something like an"atom arc " type ignitor which usually are reasonabley priced .There are a few after market coils on E-Bay ,another option perhaps .
From what's been said already about failing after it gets hot suggests it's an ignition failure .
Another thought is it could be a self advancing coil which doesn't advance .I had that a long time ago on a Stihl 042 that about drove me insane figuring that out .When I get some time I'll see if my micro fiche set mentions that in the service section

 

[Steck]

I just read a thread that mentioned a control valve on the carburetor (I believe) that can stick and cause the governing issues. But what about the white smoke and burning plastic smell coming from the flywheel area? Someone suggested plugging this port with a piece of aluminum and others suggested scrapping the ignition system and replacing it with a coil/module combination. If I get time this week, I’m going to inspect for any obvious loose bolts, cracks in the intake tube and carburetor. I’ll see if it starts and runs well. One thing I know is that it has lost its ability to govern itself so I think that might be the control valve issue. I’ll report back with my findings.

 

[Al Smith]

White smoke would usually be oil .That could be the case bolts need tightened up because if the oil leaks into the crankcase it will smoke and might in fact cause an air leak which will cause all kinds of problems .Looks to me to be 10 case bolts M5 x 18 .Slot headed screws because of the age of the saw .If that's the case I'd suggest replacing them all with torx heads .

 

[av8or3]

I have a box full of good coils for that saw, as well as a trigger unit or two.
You have to spin them up fast, faster than you probably think to get spark if you’re testing on the saw. Use an electric drill motor to spin it. And spin it fast.

 

[Steck]

Ok thanks guys. It did blue smoke a bit the morning I started it up after it sat all night inside my cold truck. I didn’t know if that was just a bit of normal start up with 40:1 or if bar oil is getting into the crank case. I may just have a multi faceted cluster F of a problem. Thank you for all the advice so far and I’ll try to get after this thing soon.

 

[Steck]

Oh and this thing seems to have a nice combination of torx (or are they Allen) and slotted. I do think I recall the case screws being flat slotted. I agree on replacing them. Is there a torque spec for these or am I going German style nizentite.

 

[Al Smith]

That control valve is what most call a rattle ball governor .Two carbs are listed for that saw OEM and both indicate a rattle ball .It works by opening up another orface at some predetermined speed to richen the mixture up to limit top speed .They work from vibrations produced at those speeds .This method was used on several models or brands of saws during that time period . They can be defeated using several methods .However if they work as designed and considering that saw in this day and age is rare I'd leave it alone .

 

[Steck]

Yeah Al. I do want to keep it original if it’s easy and somewhat cheap to do so. Up until now, aside from rebuilding the oil pump assembly, this thing was the best running, 100% on point machine I’ve ever owned. It runs the same no matter the weather, how long it sits, whatever. It just starts and cuts like hell. I desired to change nothing. It’s heavy but it’s Cadillac smooth. While my 460 is screaming it’s brains out and jumping around, the 076 just torques it’s way through. I’m hopefully going to pull some things apart tomorrow morning so I can start verifying part numbers. Side note: I don’t know whether I’m embarrassed or proud to say, I believe this thing had the original plug in it when I changed it the other day. Bosch made in Germany stamped right on it.

 

[Al Smith]

You hear stories of bad plugs but I've very seldom had a bad one and never on any engine using a magneto ignition .I've got a spark plug sand blaster I use on occasion and plugs from tiny little M8 up to I think 7/8" threads used on old tractor engines and maybe model A Fords .

 

[lehman live edge slab]

Since this saw runs the same style pump as an 041 I’d check the o-rings on the pump. They were known to go then the saw could burn bar oil because it could suck it through the pump housing in the case.

 

[lehman live edge slab]

 

[lehman live edge slab]

 

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[lehman live edge slab]