How do you "tune up" a hard-to-start Craftsman 18" chainsaw

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On 8/21/2010 3:46 PM, SF Man wrote:

You can always try the compressed air trick. If it won't run on compressed air, there could be an internal problem with the piston and rings.
TDD
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On Sat, 21 Aug 2010 16:34:27 -0500, The Daring Dufas wrote:

I didn't want to say this but I totally didn't get the compressed air trick. How are you going to COMPRESS the air in the spark plug hole and keep it there? The second you remove the air gun, the air will blow out the open spark plug hole. And, even then, with no spark plug, what's gonna ignite the mixture inside?
I just didn't understnad it at all? Sorry.
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On 8/21/2010 6:01 PM, SF Man wrote:

All reciprocating (piston) engines are basically air pumps. The characteristics of a two cycle engine allow you to run it on compressed air. You hook an air hose to the spark plug hole, feed it with a steady supply of compressed air, pull the starter cord and the engine will run on the compressed air. The pressurized air is taking the place of the explosion of fuel/air to push the piston down. A two cycle engine exhausts every time the piston goes down which is why the compressed air can be used to run it. When I check a two cycle motor with air, I stick a rubber blow gun tip into the spark plug hole and hold it there. I don't run it for hours, just a minute or so in order to test the ignition for spark output and make sure there are no problems with piston and rings. It's not rocket surgery. 8-)
TDD
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On Sat, 21 Aug 2010 19:08:40 -0500, The Daring Dufas wrote:

LOL!
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On Sat, 21 Aug 2010 19:08:40 -0500, The Daring Dufas wrote:

Ah. Now I understand what you're saying. Thanks for the details.
I tried blowing about 50psi compressed air into the spark plug hole ... with mixed results (my compressor doesn't go higher than that).
- If the piston was at the top, it fluttered (see details below). - If the piston was at another spot, it blew out the exhaust. - If the piston was at yet another spot, it blew out the carbeurator.
But it never did run the thing (I think because of the pull-cord clutch mechanism because it 'looked' like it wanted to spin but couldn't spin. Probably because it wasn't fast enough to make the pull-cord clutch disengage.
So, I think the "fluttering" was the piston trying to turn the crankshaft but it couldn't because of the pull cord. I guess I could remove the pull cord and test it without the pull-cord clutch...
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On 8/22/2010 7:15 PM, SF Man wrote:

If you'll look up how a two cycle engine works, you will understand why the air came out where it did. The position of the piston is what acts like the valves in a four cycle engine by uncovering the intake port or the exhaust port. If the reed valve is good, there shouldn't be any air coming out of the carburetor. Here's a link to an animation that shows how a two stroke engine works:
http://science.howstuffworks.com/transport/engines-equipment/two-stroke2.htm
http://preview.tinyurl.com/33qdr5p
A bad reed valve could keep it from running on compressed air.
TDD
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On Sun, 22 Aug 2010 20:30:10 -0500, The Daring Dufas wrote:
This is the California Poulan owners manual for my Craftsman chain saw. http://www.billious.com/ipls/pwe/pp3516%2Cpp4018_om_2005-06-03.pdf
Unfortunately you can't adjust anything when/if the carb gets clogged.
It's California's way of stimulating the economy while saving the environment.
It either works or you throw it away and buy a new one every two years.
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Now you got it! It even has a name: planned obsolescence.
nb
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On Mon, 23 Aug 2010 17:51:08 +0000, notbob wrote:

and it's just great for the environment, all that taking stuff to the dump and making replacements...
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On Aug 23, 11:39am, Jules Richardson

I just fixed the wife's 31 yr old Kitchenaid dishwasher (motor bearing and seal kit). You can't buy 'em as good anymore. Hobart made a fine machine.
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Be more definitive. Did it puff past you finger/thumb, regardless of how hard you pressed to stop it? If so, that's enough compression.
nb
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On Sat, 21 Aug 2010 21:41:19 GMT, notbob wrote:

No. I could easily hold my thumb on the hole. It puffed like the way you would blow a fly off your wrist.
Of course, it's only a 40cc engine ... so I'm not sure how much compression it should have.
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It will have enough to be unequivocably noticeable. Now, this doesnt always mean rings.
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SF Man wrote:

Unless you ran it without oil in the gas or without the air cleaner I'd not worry about the compression. If you can't get it running to your satisfaction with the OEM carb then what you might want to do, if you use this thing very much, is find a retrofit carburetor for it. Something like this, you will have to cross reference things and make sure it will work with your engine. Engine size, bolt patterns, throttle linkage, fuel lines etc. Notice these have low and high speed adjustments. No primer bulb on these, you shouldn't need it or the side plate with the primer bulb from your carb might fit on one of these. http://cgi.ebay.com/WALBRO-WT-20-CHAINSAW-CARBURETORS-2-POULAN-GREAT-/140440893883?pt=LH_DefaultDomain_0
All in all you ought to be able to get your OEM carb working well enough, sometimes a bread tie, the wire in a bread tie is useful to try to clean the little holes in small engine carburetors or a single bristle cut off from a wire brush will work. Have fun.
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Before you give up, remove the spark plug, squirt or pour some motor oil into the cylinder, and cycle the engine a few times, rotating it around so the oil gets everywhere in the cylinder coating rings and cyl wall, then press your thumb down hard on the open spark plug hole. Make sure you have the hrottle wide open, then try again.

Size of the cylinder has no bearing on amount of pressure. A two stroke engine needs a minimum amount of compression pressure to get good combustion. As an old 2-stroke motorcycle mechanic, I can assure you that "minimum amount" will blow past your finger/thumb no matter the cyl size or how hard you resist. It's truest "rule of thumb" ever. ;)
nb
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On Sun, 22 Aug 2010 01:29:48 GMT, notbob wrote:

That makes sense. I practically filled the thing with carb cleaner today. I'm letting it all dry out before I try again.
If this last ditch effort doesn't work, plan B is to bring it to a shop for an estimate.
Plan C, is to buy a NON-CALIFORNIA chain saw on the net. Can you recommend a good place to buy chain saws (NON CALIFORNIA EMISSIONS) that actually have adjustable "L" low and "H" high screws for the carb?
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Sorry, but I've had little to no experience with chainsaws and 2-stroke yard tools, despite their being the same engines. In fact, I had a terrible time with the chainsaws and gas trimmers I inherited when my brother passed away. I couldn't get any of them to start, either, mainly cuz they were all junk, with cracked primer bulbs and hardened broken fuel lines and cracked plug wires. There's some real crappy merchandise being foisted off on the public, these days. :(
nb
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On Sun, 22 Aug 2010 17:18:49 -0700, SF Man wrote:

Check that the gasket between the carb and engine is good, that the carb is bolted on tightly, and that the crankcase cover[1] is bolted on tightly and with a good seal. On most of these engines the carb's fuel pump runs from crankcase pressure, so if there are any leaks in the system all sorts of strange things can happen - after ruling out spark and fuel line/filter, I'd try there next I think.
Also pull the flywheel; it might be that the flywheel key has sheared and the timing's out a little - maybe not enough to stop it running (with a loss of power, but that might not be noticable), but enough to make it hard to start.
[1] taking the cover off for a moment just to see if the bore is damaged might not be a bad idea, either.
(re. compression, I posted here about a 4-stroke mower engine earlier in the year; that one turned out to be compression loss due to bore damage, even though it felt like it had "enough" compression when I stuck my thumb over the spark plug hole)
cheers
Jules
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I would recommend you go straight to "B". An honest saw mechanic can either fix this rascal quickly, or he can tell you it isnt worth fixing.
I never bought a saw on the net. My first chain saw was an Echo, and it was a heck of a good saw. Then I bought a Husqvarna (also a great saw, stolen by a couple of drugheads), and then a replacement Husqvarna.
I dont know if an internet company CAN ship a noncomplying saw to California.
Note that some saws have what they used to call 50 hour engines. That is about the life expectancy of them.
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On Mon, 23 Aug 2010 09:51:13 -0500, hls wrote:

Or you get a "Friday engine", assembled by someone who is itching to get away for the weekend and so not paying as much attention to their work as they should :-(
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