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

If the plug is hot, it's prbably firing. You can check this by pulling the plug, resting it against some metal and hold the saw steady while you yank the cord (have someone help, just keep them away from the blade!)

If it sparks, start looking for fuel not getting there.

Um, when I was in telephone support, they told us the FIRST question to ask was, Is it plugged in? I said, "you're kidding!" 30% of most problems were because it wasn't...

So, full tank? Fresh gas? And, is the fuel shut off closed?

Hmm. If the spark plug comes out dry, that's a good clue.

You could put a couple drops of gas mix into the spark plug hole and see if it runs for a second or two. I've also sprayed ether on the air filter, that is a symptom check for fuel starvation. Only want to run it for an instant, as the saw relies on the oil mixed in with the gas to lube the crankcase bearings, rod bearings, and piston rings.

The R means it has a series resistor for EMI suppression. Probably does not make much difference either way.

Turn the thing over with the plug removed from the engine, but sitting on top of the engine to make good electrical contact. If you see a nice hot spark, you have good magnetos. If you don't see a spark, your magneto or points have an issue.

Magnetos don't fail very often, but it happens. Fuel systems clog all the time, constantly.

--scott

Husqvarna, and some other chain saws, have had problems with the plastic gas line inside the gas tank cracking. When it does, the saw will be hard to start or not start at all. In many of these saws it is easy to replace the plastic tube with one of better quality, and replace the filter at the same time. A saw shop can do it for you, if yours is bad, or will sell you the improved fuel line.

You can check the ignition by pulling the start cord and observing the spark plug gap. Naturally you have removed the plug and have it touching the electrical ground of the chainsaw.

Thanks for the tips.

This is apparently a Poulan motor in the Craftsman chain saw.

The three fuel lines appear clear and unbroken. Chain saw is only a year old. Fuel filter appears unclogged when I blow on it and has no visible deposits. It's bright white. When I press the bulb, gas flows (I can tell because I emptied it accidentally while I was holding it in my hands and it filled right up with gas).

Gas is new. Mix is new.

I'm working on the carb screw as I type ...

It is not easy to see the crack in the line. Several models of chainsaws have had the problem, and it is not at all unusual from them to go bad within a year.

But the bottom line is to be sure you have fuel and spark, and if either is missing, you have to work backward to locate the problem. Remember the basics...you have to have spark (hot and at the right time), fuel, and compression to have the engine run.

I just realized that just before it stopped running, it ran really really fast. Of course, I had protective headgear on, but, even then, thinking back, it was running really fast.

I wonder ...

I wonder if I blew the rings somehow.

When I put my finger over the hole after removing the spark plug, and pulled the starter cord, there was only a small puff. Noticeable. But small.

Do you think compression might be the problem?

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

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

I once read about guy who was having a problem with his chainsaw.He used a drill bit and cleaned out the carbon in the exhaust pipe.He said it ran ok after that. cuhulin

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.

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.

It will have enough to be unequivocably noticeable. Now, this doesnt always mean rings.

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

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.

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.

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

LOL!

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...

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?