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Thread: Stihl won't start
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10th March 2015, 02:24 PM #1Senior Member
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Stihl won't start
Hi all,
You may remember a while back I posted a thread about a Stihl 090 which was given to me for use as a slabbing saw.
Well I tracked down a retired mechanic who replaced the piston, reconditioned the carby and gave it a general overhaul.
I couldn't wait to try her out and then I had the opportunity to slab up a silky oak roughly 600 dia.
The first 2 slabs went well and I was very happy with it's performance, however she decided not to go after that, now very unhappy.
When it was cold I gave it a couple of squirts with "start ya bastard" and a way it went, now thinking all is good.
Had another chance to slab a large Lemon Scented Gum and this time the saw stopped halfway through cutting the first slab, even more unhappy.
Pulled the saw out of the slab and gave it a couple of squirts but to no avail even after several attempts.
Seems as though this saw just doesn't want to lay on it's side, thinking there is be fuel problem of some sort?
Just wondering if anyone has had a similar problem or can suggest any diagnosis before I take it to a small motor service.
Thanks in advance.
Nev
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10th March 2015 02:24 PM # ADSGoogle Adsense Advertisement
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10th March 2015, 03:11 PM #2
With the two strokes the problems stem from fuel, spark and compression in roughly that order. Most likely is you've got dirt in the carb or a fuel saturated diaphragm. Replace or clean the air filter, often a problem with saws. Next check and if needed replace the spark plug. If the plug is fouled replace it. Do you leave fuel in it when not in use? Try cleaning the carb and if it still won't run install a carb kit. Does it have good compression? If not replace the rings. Lot's of other things could be wrong such as detached cc vacuum tube, sheared flywheel key, clogged muffler, magneto defect, bad plug wire and so on.
Innovations are those useful things that, by dint of chance, manage to survive the stupidity and destructive tendencies inherent in human nature.
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10th March 2015, 03:18 PM #3GOLD MEMBER
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Modern fuel does not take nicely to being left in the tank or carbi.
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10th March 2015, 08:50 PM #4Senior Member
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Thanks for your reply Rob,
A coupe of things I forgot to add in my original post, that being:
1. I replaced the spark plug
2. The retired mechanic replaced the rings (not the piston)
Your reply will certainly help when talking to the small motor guy I will be seeing.
Cheers,
Nev.
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10th March 2015, 10:59 PM #5Innovations are those useful things that, by dint of chance, manage to survive the stupidity and destructive tendencies inherent in human nature.
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10th March 2015, 11:16 PM #6.
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When cleaning an air filter with a compress the safest way is to blow at right angles across the filter rather then directly at the filter. There should be enough air flow to clean but not damage the filter.
I doubt it will be the air filter. Those big saws (like my old 076) can run with a half inch layer of sawdust on the filter. It just makes them run a bit richer than usual.
One of the things that can cause what you are seeing is a leaking crank case or impulse tube.
The impulse tube should be replaced periodically if it hasn't be done.
Did the mechanic perform a crankcase pressure test? This should be SOP after changing the rings.
You say it doesn't like running on its side - will it start and run in the upright position?
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10th March 2015, 11:43 PM #7Bit of a Tool
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Did it bog down before it stopped. Mine did today as it was being pinched in the cut by the slab I was cutting. First couple of slabs were holding up a nice wide kerf behind the saw so I forgot to keep checking to see if it needed wedges. Anyway that would not stop it from starting after you pulled out. Clean carby and fresh fuel?
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11th March 2015, 09:38 AM #8
Carby needs work.
Use fresh fuel.Cliff.
If you find a post of mine that is missing a pic that you'd like to see, let me know & I'll see if I can find a copy.
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11th March 2015, 01:58 PM #9Senior Member
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Thanks for your reply BOBL,
The air filter in the saw is virtually brand new & quite clean.
The saw runs well when upright, but I did notice a bit of fuel leaking when it was on its side & I'm sure this has something to do with it stopping but can't be sure.
The fuel wasn't the freshest but wasn't that old either.
The retired mechanic did say that these old big saws can sometimes boil the fuel in the carby, whether this is true or has anything to do with it stopping I don't know.
I'll reply when I get a diagnosis from the saw doctor.
Cheers,
Nev
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11th March 2015, 03:33 PM #10.
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No worries
The air filter in the saw is virtually brand new & quite clean.
The saw runs well when upright, but I did notice a bit of fuel leaking when it was on its side & I'm sure this has something to do with it stopping but can't be sure.
The fuel wasn't the freshest but wasn't that old either.
I used to put the old fuel in my car and top off the tank immediately but now we have diesel vehicles so I can't do that. Recently I bought a whipper snipper and I use the old fuel in that.
The retired mechanic did say that these old big saws can sometimes boil the fuel in the carby, whether this is true or has anything to do with it stopping I don't know.
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11th March 2015, 08:27 PM #11
I used to into model aircraft with similar fuel systems, plastic tank, flexible fuel lines with a clunk pickup, fuel either pumped to carby by impulse tube operated pump or more commonly, system pressurised from exhaust (glowfuel, not as volatile as petrol based fuels so very little chance of blasting the tank contents).
Problems like you have been experiencing, (start run OK in normal position, cut out when orientation changes and unit has run maybe 5-10% of tank contents through creating an air gap) were generally related to a pinhole, nick, cut etc in the fuel supply tube within the tank. Not an issue with a full tank as the defect is submerged in the fuel, not a problem initially when you change orientation as it is still submerged, but at some time during the run, normally early on, the defect emerges from the diminishing fuel reserve into the air space in the tank and sucks small amounts of air, which causes the fuel in the line to foam resulting in a lean run and eventual stopping. Often the hardest part of the system to get to, so the last to be checked. New plumbing in the tank and the problem generally disappeared and a very quirky motor became quite quite predictable and reliable.
For a quick check try comparing viable run times in vertical position and horizontal position, a significant difference often indicates a leak in the tank internal plumbing.I used to be an engineer, I'm not an engineer any more, but on the really good days I can remember when I was.
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12th March 2015, 01:56 PM #12Senior Member
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Thanks for your input malb, I will certainly be giving this information to the mechanic as well.....
Cheers,
Nev
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