Craftsman 18' 42cc chainsaw won't start but has spark

bdawg8569July 27, 2010

Hi everyone,

I am seeking some help with a craftsman chainsaw. I don't know what model it is. I haven't looked closely for it but it doesn't appear to be real obvious either. The saw came from an auction so i don't know the history of the unit. It wouldn't start when i got it home, so I began the diagnosis process. It has spark when the plug is taken out and grounded, however, I have not been able to get it to even pop off on starting fluid.

I found another post for a guy that said perhaps it was not sparking at the right time, possibly due to the fact that the key on the flywheel was sheered off. I took mine off tonight and everything looks great there. This saw looks like it was barely used.

They suggested that I take off the muffler as well and make sure the piston wasn't grooved from running too lean. As best i can tell it looks ok to me, though i'm not experienced with small engines. It has good compression, so i am at a loss as to why it wouldn't atleast fire up for a second with the starter fluid.

I would greatly appreciate any other ideas or possibilities that i could try. Thanks in advance,


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..Take off the air cleaner, make sure the choke is NOT on.
..Set the trigger lock to high/start speed
..Remove the spark plug
..put about a teaspoon full of mixed fuel into the spark plug opening.
..quickly replace the plug
..pull the pull start and keep pulling until it pops. It may even run for 2 or 3 seconds.

If it did give indications of starting, your problem points to fuel not being delivered by the carburetor. There are a number of reasons this can happen. Chain saws for homeowner use have a tendency to sit for long periods between uses. If fuel is left in there, it can turn to a shellac like sludgy substance and plug the various ports where fuel and air enter and mix. In the tank, the fuel line terminates at a small filter. It could be clogged with the sludge.

If you are handy, remove the carb. and using the ether (starting fluid) soak the carb inside and out to clean the shellac off. Remove the the air/fuel mix screws and using the nozzle on the ether, spray it into the holes until it starts coming out from within the carb. Put the mixture screw(s) back in but be careful when tightening them. Once you feel it bottom out, turn the screw back out 2-1/2 turns. This will at least allow the engine to start and then you can fine tune the fuel mixture once it's running.

Another problem with the fuel sitting in the carb for any length of time, is some of the newer fuel mixture. If you are using a fuel that uses ethanol, it will cause the aluminum to corrode and pit. It is also recommended to use 89 0r higher octane. If the saw had NOT been using ethanol gasoline, over time a shellac coating forms. Using the ethanol gas, starts cleaning this coating off the carb and serves to clog the ports. That is basically what is in those carb/fuel injector cleaners, along with a little naphthalene (lighter fluid). Ask anyone who has a motorcycle that never used ethanol gas and then used some!!!! It takes forever to work it out and in most case, the carbs have to be removed and disassembled and the ports unplugged. The same can happen to fuel injectors on your car although, consistently using the ethanol fuel or fuel injector cleaner, and running about 250-300 miles at interstate speeds will usually solve THAT problem.

If your saw has a primer bulb, make sure it is not cracked or otherwise leaking. If it is, replace it. You must have the bulb on the saw for it to run, it acts as a float bowel. Also make sure there are no cracks or kinks in the fuel line.

Once the saw gets running and warms up, let it idle and adjust the LOW mixture screw until you get the smoothest run. The idle speed screw is another you need to adjust. Adjust the idle speed at a speed where the saw chain does not move. Then, squeeze the trigger a bit and moving the HIGH mixture screw in or out, a little at a time, adjust until you get the smoothest run. Be careful at the higher speed since the centrifugal clutch will engage and the saw blade will begin moving requiring you to hold the saw in place more forcefully.

When checking the spark plug, was the spark yellow or blue? If it was yellow, there is too much resistance to the plug or, the spark needs to be adjusted. If it was a blueish spark, that is generally a good spark. If the above gets things going for you, I suggest replacing the plug. They are CHEAP, LESS THAN 5 BUCKS.

As with any engine, don't leave fuel sitting untreated for more than 3 months. Follow the directions on the label of a product such as STABLE. You'll notice now days, it has a blurb stating a new formula for ethanol fuels. Even though they claim you can leave it in there for a year, I wouldn't do that. On your saw, allow the saw to run empty until it stops.

Be sure to use fresh gasoline and the correct fuel/oil mixture on your saw.

    Bookmark   July 28, 2010 at 6:24PM
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Thanks for taking the time to post. As I mentioned in my first post, i was unable to get the saw to even pop with starting fluid. I tried your suggestions, but to no avail, tho not surprisingly cause the starting fluid was the same test. I did find out that the model of the saw is 358.350480. I was unsure what you meant about setting the trigger lock to high/start speed. I assume that you thought maybe this model had a trigger lock for the throttle? I realize you didn't know the model at the time of writing but there isn't a throttle lock on this one, or maybe i'm misinterpreting what i was supposed to do. I found a manual online and didn't see anything about trigger locking.

Your information about the carb or fuel system being the problem was right on, that is why i had begun testing with starting fluid in the beginning. I am just puzzled as to why the engine would not atleast pop off since it has good compression and good blue spark. I am baffled here. I am no small engines expert by any means, but i have had good luck working on a few weed eaters, but this one really has me stumped. Any other ideas i can try anybody?

    Bookmark   July 28, 2010 at 7:36PM
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How are you testing the compression? Resistance to pulling the starter rope is not a reliable compression test.

You said the cylinder/piston looked good---were there any marks in the cylinder or on the piston? Any lines/gouges in the cylinder/on the piston is a sign of a problem. A good cylinder is shiny like a mirror.

Try starting the saw with the muffler off. Just do not run it more than a second or two. Completely plugged muffler(bad baffle) can give you a no start.

The only other things I can think of is the coil pack is out of time or the spark plug is defective. I have seen plugs that will show spark out of the engine, but not under compression.

    Bookmark   July 28, 2010 at 11:55PM
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Thanks for the advice. I think it was one of your posts from another thread that got me started doing the things i have done thus far. Resistance to pulling the starter rope and just putting my thumb over the carb hole is the only way i have tested compression. Is there some other way i can test? I said that i think the cylinder/piston looked good. I didn't see anything but it is a small window to see through and it was kind of hard to tell. I have replaced the spark plug, so i have tried starting it with 2 plugs both of which have had spark. I tried taking off the flywheel to make sure the key was not sheered off and it was fine too. I will try starting it w/o the muffler tonight when i get home. I appreciate all the advice. So the saw wouldn't even pop off for a second if the piston or cylinder has marks on it? Thanks in advance,


    Bookmark   July 29, 2010 at 10:38AM
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If you have spark, fuel and compression, you should at least get a pop, even if it were a backfire. I would do as suggested concerning the muffler. I would also check to make sure the carb is not plugged. Without air entering, you won't get a fire.

Another thought would be the diaphragm in the carb, as far as fuel is concerned.

Usually, when these type saws are dropped (or thrown in disgust) the magneto coil moves into the flywheel. Usually when that happens, you can't pull the cord. Maybe it went into the other direction and is too far from the flywheel which contains the magnet. If the spark is more yellow than blue, that is an indicator the coil is too far away and you are getting a weak spark. Slide a piece of paper folded to the thickness of a match book between the flywheel and the magneto. Loosen the magneto and slide it forward until it is firm against the paper and then tighten it back down. Pull the paper out and you should have about a .17 space. This will give you a good strong spark.

I don't have anything in front of me so I need to ask if this unit has an electronic control module that takes the place of points and condenser. If so, you might want to look at that as a possible problem.

Good luck!!! I'll be checking in to see if someone else has an idea or, if you would be so kind, let us know what happens.

    Bookmark   July 29, 2010 at 5:22PM
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Two cycle engines are renowned for being tempermental. I have had no starts that I disassembled, inspected tested parts, and found no deficiencies. Reassembled it and it fired right off.

You said you bought the saw at an auction. There is a possibility there are some incorrect parts on the saw---like the flywheel. If the flywheel were incorrect, the magnet that triggers the coil which creates the spark at the plug could be firing the plug way out of time. Only takes about 5 degrees.

I'm trying to imagine any oddball things---the flywheel idea is really odd.

I had a compression guage for testing compression when I repaired saws.

I just had a really whacked out thought. There are rings on the piston, right? Should be at least two. A lot of chain saw pistons are just a wee bit smaller than the cylinder bore and actually could be installed by a DITer without rings and 'seem' right. Definately would not fire, tho.

    Bookmark   July 30, 2010 at 12:13AM
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I tried most everything discussed and the dang thing just will not even try to backfire or give a hint of starting. I don't know what to do. It makes a good paper weight, but thats about it. Perhaps something to shoot at with a shotgun. It's so frustrating. I guess I will have to take it to somebody that knows more about it than I do. I appreciate the help and wish I had better news, but unfortunately i don't.

    Bookmark   July 30, 2010 at 2:33AM
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I repaired a chainsaw for a coworker and his had spark, but would not pop also. Turned out his saw was notorious for flooding and when i constantly pulled the cord on choke it was continuously flooding. One day I tried starting it wide open would no choke and it fired right up. It still has times that it does not pop and i told him to move it to half throttle and BAM it starts again. Don't know why its been happening, but it works well. Has your plug been getting wet?

    Bookmark   May 1, 2012 at 8:15PM
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