Stihl 028AV Not Running

[bmp01]

3. Fitted replacement secondhand carb. Saw started and ran for a minute or two, more or less normally, then died and would not re-start despite many attempts.

 

Fuel tank vent blocked causing vacuum in tank? Unscrew the fuel cap to vent the tank.... will saw restart?

IIRC Fuel tank vent hose has two grub screws in the line with a jet sized hole through each, its situated behind the air filter.

 

bmp01

[2414Gingerboy]

Did you say you fitted a new gasket behind the carb? if so did the impulse hole in the gasket match up to the hole in the casing? Just wondered if you have inadvertantly blocked your impulse, or does this model have a separate line? in which case just ignore me.

[Talltone]

Thanks a lot for very quick comments and useful graphics etc.

 

However, I ca't see how to move along as my problem persists:

 

1. Despite a VERY CAREFUL strip down, clean and re gasket/diaphragm of existing carb (plus replacement of fuel, fuel filter and impulse lines with new OE parts).

2. Despite substitution with another pre working carb.

3. Despite adjusting rotor/magnet gap and testing to establish that spark is OK.

 

From this logic I can only surmise that fault lies in the fuel delivery to carb, which in turn implicates the impulse line.

 

If, as it appears from the videos, that there is NO valve in the primary engine system (as opposed to valving present in the carb secondary system) is it a possibility that the impulse line is blocked or restricted somehow?

 

Getting desperate now, have five multi stumps, an oak and holly tree to remove prior to spring!

 

If you can hear a high pitched Heeeeeeeeellllllllllpppp in the distance - that's me!!!

 

So grateful for ANY further wisdom.

[spudulike]

If I had a piece of equipment that my business depended on and it went wrong, I would be calculating the impending loss of income and come to the conclusion that your forte is to cut stuff up etc and not fix the more in-depth two stroke faults and hand it over to someone else whose skill set and experience is far better than your own.

 

I fix kit for customers that know that they earn more doing tree/landscaping work than trying to fix faulty kit. They get back kit that works, they go out and earn money.

 

I am not trying to be disparaging to you but just pointing out that you appear to have got to the end of the road on fixing this one. The one issue is that it is a very old saw so economic repair may be difficult.

 

Engines need spark, fuel and compression, it needs a lot more but this is the starting basis for most fault finding. A good tech will be right on your saw fault in minutes. Repair may take longer but have diagnosed customers faults in minutes in front of them!

 

Just saying and no offence meant!

[peatff]

I have an old 036 I bought to play about with. If it stopped working and I couldn't fix it its a 20 year old saw and I would go out and replace it. Get something that works and use your 028 as a project saw and buy a cheap saw for the work you need to do like my 135 or a MS181.

[paul99]

I struggled with my 028 super for a little while. It would run very erratically, especially at idle, but mine would at least always start so not sure this is going to be any use... but given you've ruled out the obvious things have you thought about bad crank seals? Apparently prone to going on the 028 and possible if they leaked badly enough the saw might not start at all (assume lack of crankcase vacuum / no impulse to pump fuel as you are suspecting). It's a bit fiddly to change them but their cheap and doesn't take long. In your position I'd just replace them or if possible rule that out with a pressure /vacuum test before admitting defeat.

 

As for testing impulse... I've not tried it myself but I've read somewhere, a long time ago, that putting a blob of grease on the end of the impulse line and pulling the saw over is a quick and dirty way to test - if there is impulse the grease will be drawn into the hose.

Edited February 17, 2017 by paul99

[bmp01]

Thanks a lot for very quick comments and useful graphics etc.

 

However, I ca't see how to move along as my problem persists:

 

1. Despite a VERY CAREFUL strip down, clean and re gasket/diaphragm of existing carb (plus replacement of fuel, fuel filter and impulse lines with new OE parts).

2. Despite substitution with another pre working carb.

3. Despite adjusting rotor/magnet gap and testing to establish that spark is OK.

 

From this logic I can only surmise that fault lies in the fuel delivery to carb, which in turn implicates the impulse line.

 

If, as it appears from the videos, that there is NO valve in the primary engine system (as opposed to valving present in the carb secondary system) is it a possibility that the impulse line is blocked or restricted somehow?

 

Getting desperate now, have five multi stumps, an oak and holly tree to remove prior to spring!

 

If you can hear a high pitched Heeeeeeeeellllllllllpppp in the distance - that's me!!!

 

So grateful for ANY further wisdom.

 

Thats a detailed analysis. But have you done Spuds suggestion in post 10 - I think its a very good test to answer some of your questions regarding fuel supply to carb. Start with clean, empty carb on the bench. Refit. Turn engine over - with out choke. Remove carb. Inspect for fuel in pump and metering chambers. If no fuel, you have the answer to your question. 30 mins tops.

 

Ditto with my suggestion above. Have you checked the tank vent hose. Blocked vent would surely allow engine to run normally for a few minutes while the tank gets into depression, then no fuel.

 

Another suggestion, you may have reblocked the filters in the carbs again. I have suffered with my 028 with a mystery gunge / slime that reappeared after the carb had been thoroughly cleaned.

 

PM me regarding tech manual if you want, but the answers here will teach you more:001_smile:

 

And please keep us posted when you find solution.

 

bmp01

[spudulike]

I struggled with my 028 super for a little while. It would run very erratically, especially at idle, but mine would at least always start so not sure this is going to be any use... but given you've ruled out the obvious things have you thought about bad crank seals? Apparently prone to going on the 028 and possible if they leaked badly enough the saw might not start at all (assume lack of crankcase vacuum / no impulse to pump fuel as you are suspecting). It's a bit fiddly to change them but their cheap and doesn't take long. In your position I'd just replace them or if possible rule that out with a pressure /vacuum test before admitting defeat.

 

As for testing impulse... I've not tried it myself but I've read somewhere, a long time ago, that putting a blob of grease on the end of the impulse line and pulling the saw over is a quick and dirty way to test - if there is impulse the grease will be drawn into the hose.

 

The bottom end produces both pressure and vacuum so the grease will be sucked in or blown out depending on where the stroke of the piston is.

 

You should be able to either blow down the impulse line or blast some WD 40 down it and see if any leaks out but a simple check is a vacuum and pressure check and this will verify the manifold, impulse and seals. Any good tech will be able to do this!

[spudulike]

BTW, these saws were produced from 1977 to circa 1993, even if the saw was a later model, it is 23+ years old and is now more suited as a weekend warriors logging saw than a professionals primary saw!

 

Think the earlier suggestion if keeping it as a project saw and buying a later model may be a sensible option, especially as spares are probably rare now!

[bmp01]

BTW, these saws were produced from 1977 to circa 1993, even if the saw was a later model, it is 23+ years old and is now more suited as a weekend warriors logging saw than a professionals primary saw!

 

Original post says "Have used my 028AV over about 10 years for domestic tree felling and woodcutting. " = Weekend Warrior.

Nowt wrong with his choice of saw for his use, 028

He is an engineer, I'm sure he'll get some satisfaction from fixing the thing