Mysterious problem Stihl 038 AVS

[Charles Ekin]

Greetings

 

Please help!

 

I'm tearing my hair out trying to find the cause of the problem that I am having and after loads of research and ideas from various people, many spare parts and tests later, the problem persists. I am making this final appeal to your collective wisdom and experience before I go nuts!!

 

To see the saw in action and the problem that I have with it cutting out, please go to the following You Tube clip which my son filmed;

 

[ame=http://www.youtube.com/watch?v=ZFfTfUWPwhY]Mysterious problem with Stihl 038 AV super chainsaw - YouTube[/ame]

 

The problem: The saw cuts beautifully in the usual vertical position but cuts out when turned horizontally into a typical felling position. It does however work well when turned into the other horizontal position.

 

What has been recommended to me: It’s a) an air intake issue which is affecting the mix, b) leaking crankcase seals, c) leaking impulse line or d) scoured piston and cylinder causing temporary compression issues.

 

What I have changed or had done:

Fuel system:

New fuel tank breather

New fuel line and filter

New carb diaphragms and gaskets (no other damage or wear visible to rest of carb)

New air filter

The carb boot (or elbow connector) has been removed, checked for damage and reconnected.

 

Piston and cylinder:

While the tank housing was opened away from the engine, the exhaust was removed and the cylinder and piston are in virtually mint condition.

 

Crankcase:

The crankcase has been professionally pressure and vacuum tested and passed both.

 

Impulse line:

No apparent sign of cracking or splits but replaced anyway.

 

So, please have a look at the video. Here’s the link again: [ame=http://www.youtube.com/watch?v=ZFfTfUWPwhY]Mysterious problem with Stihl 038 AV super chainsaw - YouTube[/ame]

 

The saw is only used for firewooding but I want to use it for felling as well but cannot due to this problem.

 

Your help would be really appreciated.

 

Many thanks

 

Charlie

 

PS Although this is a new thread, some of the information in the "Stihl 038 AVS Replacing Elbow Connector" thread relates to this, with some great comments but....My hunch is that it is the crank seals in which case why did it pass its pressure and vacuum tests? Anything else I might be overlooking?

[Adamam]

Probably a stupid and obvious question, but definitely not rich mix pooling in the crank case?

[Rich2484]

It may be crank seals but as you turn the saw on its side the seal are allowed to move out of position, when the saw is other way up the seals are pushed into there position. If you have replaced everything else and the seals are the only thing left then change them. The mix is definatly ok?

[Charles Ekin]

Thanks for the reply, Rich. The mix is bang on. I even tuned it whilst it was at full throttle and cutting to get the bubble just right. Idles perfectly and accelerates swiftly. Spark plug dark brownish, not black and sooty.

Charlie

[Rich2484]

Then it has to be seals, can't see anything else. All the other parts changed sounds like it should be a new saw now. Lol

[spudulike]

Sounds like most of the normal items have been done but obviously haven't cured it.

 

The pressure and vac check should immediately tell you if the crank seals are bad or on the way out - did you see this being done?

 

The pressure and vac test will also tell you if the impulse line or carb boot is holed, if the test has been done correctly, the saw should be air tight - did the tester move the crank shaft round whilst the saw was being checked? This should be done to fully test the seals.

 

From your video, it looks like the saw when in the felling position, runs out of fuel and then, when trying to start it, it doesn't start right away like a warm or hot saw should. When hot, does the saw start right away on the first pull?

 

One thought is that the fuel line is non standard and is shoving the fuel filter in to the filler end of the fuel tank so when on its side, it dies - well worth a check.

 

My other thought is to let the saw die in the felling position and then strip the carb down immediately and see where the fuel is in the carb - pumping section, diaphragm or neither! Worth checking the colour of the plug and if it is wet or dry as well.

 

Are the AV mounts OK? I once had a Husky that would over rev when held downward and it was shot AV mounts but think probably not!

 

I have heard of the crank seals having this effect but it usually manifests itself as poor idleing and over revving.

 

IMO, it looks fuel related and looks like it runs out of fuel.

 

Where about's in the country are you, I do one or two saw repairs for members who have run out of patience, luck and usually pick up the problems no one else has fixed or want - story of my life:001_rolleyes: you may find one of the other guys/sponsors are local to you and can assist!

 

Let us know how you get on!

[Stubby]

I had this with a Husqvarna long reach hedge cutter . It used to " apparently run out of fuel when there was 1/3rd of a tank left . It also cut out when tilted one way , I can't remember which . It was , as suggested the fuel line in the tank . The filter had got trapped in a certain position lifting it out of the fuel when at 2/3rds empty or wen tilted in the position that left it un covered . Soooo could be that . Get a bit of welding rod or similar and make a hook and lift the filter out and reposition it , maybe ?? The only other thing that comes to mind is a dodgy stop switch / wire connection . It could be making then breaking when you tilt the saw . Just a thought . If it was me I would just give it to spud . He will sort it no danger !

[GardenKit]

I agree with all the others, which is not much help really. It does, as Spud says, sound like its running out of fuel.

 

With regards to the fuel pickup pipe, I have just had a look at one on my bench and TBH, if the pipe is genuine Stihl the filter cant really get stuck anywhere. The hose is only about 75mm long inside the tank and the filter falls neatly to the bottom, or the RH side when in a felling cut. The filter does need a little weight to it, some non genuine ones can be a little too light.

 

I notice that the inlet manifold (boot) has not been renewed, just replaced. I recently had a 440 with similar symptons. The boot had a small hole which opened when the saw was on its side and the AV rubber flexed. The boot was old and hard and did flex well when the AV,s did.

 

This however caused a weak mixture and loss of power, but did not die like yours, which, as said sounds more like a fuel issue.

 

Good luck

[elfinwood saws]

does it die, even with the fuel tank full? is it lack of fuel or to much fuel, when it cuts out? Have you tried a different carb?

[Charles Ekin]

Really chuffed that you have all gone to so much bother to try and help me with this. Thank you.

 

To answer a few questions:

SPUD

I didn't see the vacuum and pressure test being done, just left it with a Stihl agent and then picked it up. So although I could ring them up and find out what the bloke did, I don't as yet, have any info apart from the fact that, as it was already half stripped down, I gave it to him with the tank housing pivoted away from the engine with the carb boot off. He told me that he changed the pressure through the impulse line nozzle and blanked off the intake manifold.

As far as how it starts hot is concerned, as long as it is in the normal cutting position, it starts on the very next pull.

The fuel line is a standard Stihl spare. Just to be sure, I did what you saw in the video with a completely full tank of fuel and it still behaved in exactly the same way. So I think that rules the flopping fuel filter thing out.

I'll certainly have a go at checking out the spark plug when it cuts out. I haven't heard of checking the carb though. Can you give a bit more advice. Do I take the whole thing out, remove the covers both ends and take the diaphragms out? What am I looking for?

Kind offer to "pick up the pieces". I am in Farehamn near Portsmouth.

 

STUBBY

Thanks for your post too. The HT lead, the earth wire and the cut out wire all had wear to their insulation so I changed all of them too! I really am clutching at straws!

 

GARDENKIT

Thanks also. As far as the boot is concerned, can a really close inspection with 20/20 vision miss a hole or a tiny crack? If it can then I'll just chuck that in as a next part to replace in the hope that it might work. I'm only a bit reluctant because they are about £25-£30 ex vat

 

Anyway, many thanks to you all again and any ideas in light of what I've just said would be very gratefully received.

 

Cheers

 

Charlie