what am I overlooking?????

Several years ago, in a weak moment, I bought a Poulan 20" chain saw because it was on sale for a price I couldn't resist. I started it up once, made a test cut in a log to make sure it was functioning OK, and put it back in the plastic carrying case.

With my two Stihl saws, I simply never needed a 20" saw. Last week I noticed the case sitting there under a bench in my shop and figured I'd start it up once. Put fresh gas in it, but no go. I finally took the side cover off and put a drill on the flywheel nut and spun it that way. Still no go. I finally checked the spark plug and it was wet so I knew it was getting gas. Checked the ignition with a test light and it was dead. On/Off switch was "On". This is about as simple of an ignition system as there is possible. The magnets on the flywheel pass the primary winding of the coil, the primary induces high voltage in the secondary, and the plug wire is embedded in the secondary of the coil. The "Off" switch grounds the secondary of the coil.

Since I know from first hand experience that Poulan had a rash of defective coils about the time this saw was manufactured, I finally decided the coil must be the culprit and ordered a new one. Even though the saw is new and has run only about ten minutes, it's too old for warranty, if Poulan even honors their warranties. I installed the new coil this noon and still nothing.

I've disconnected the "Off" ground wire at the coil to eliminate that. I pulled the flywheel to check the key and that was good, although if the key were sheared, there would still be spark when the flywheel rotated, just at the wrong time. Both the original coil and the new one check the same with an ohmmeter, and they both checked the same as the coil I pulled out of a defunct weedeater that I abandoned because of fuel problems. (The weedeater coil won't interchange, but it's made the same).

I'm stumped. The entire ignition system consists of the rotating flywheel, the coil with the plug wire embedded, and the "off" wire to ground the coil to stop the engine. It's such a simple ignition system, the only thing I can think of is that the new coil might be defective. I think I'll take one of the coils to a small engine shop tomorrow and see if they have a better way of checking coils, or at least double checking my conclusions with an ohmmeter.

As I said, am I overlooking something?

so you are saying it does not use points/condenser? Didn't see those in your list of ignition components. Only thing I've ever seen create your problem from just sitting is points "scumming over". There's got to be a switching/timing device either points or EI.

Have you put a plug in the plug wire socket, grounded it against the engine and checked for a spark> May require a helper or some sort of clamp

yep.

No points or condenser. Being unable to find anything else, I'm assuming an electronic ignition module is embedded in the coil assembly. Timing is built in by the key in the flywheel.

Hi Goose, have you tried the fine sand paper trick on the flywheel and coil pole pieces? Friend of my Dad's used to run a small engine shop. Chain saws, lawn mowers, outboard motors and etc. Any engine that was brought to him with symptoms like yours his first try was fine sand paper on the flywheel and coil pole pieces.

JimB

Take the whole saw. Where I work there is no other way to check for spark without the coil on the saw where you can spin the flywheel past it.

The only other thing I can think of is be sure the coil is grounded well where it mounts. wouldn't hurt to hit the mount posts with some emery cloth or a wire brush.

I'd thought of that, but this is basically a new saw. Nothing is dirty/rusted yet.

Have you checked to see if the magnetic pole in the flywheel is still magnetized? Those things can get weak after a while. Rust or other corrosion on the magnetic section can also inhibit the spark. Air gap is also important. I think it should be around .010" to .015" if I remember correctly. Also make sure that the KILL wire is not grounded out. After checking all of that, take out the plug and spin it over with a drill and you should get a good healthy spark. There just isn't a whole lot to those ignition systems.

Did you check for spark with a new plug or the one out of the saw? Just wondering if the original plug is fouled with several year of gas

Did you check for spark with kill wire disconnected?

I'm going with the "defective part" theory. Especially if the coil was made about the same time as the original one. Could have been some bad assembly, some defective electronic components. Whatever happened was age related, not use related.

jimb, the "little bit of rust is gonna screw everything up theory" is simply NOT true.

You don't have to take my word for it, the engineers at B/S concur.

Of course, it takes more than engineers or science or REALITY to make "old mechanics' wives tales" go away!

The following is quoted word-for-word from the Briggs website.

"Ignition Coil

The ignition coil is probably the easiest thing to check and therefore the first thing to check when embarking upon ignition system troubleshooting. Install the 19368 spark tester between the high-tension lead and a good engine ground. Spin the engine over (at least 250 RPM) and watch for spark in the tester window. As simple as it seems, this is a fairly comprehensive test.The tester electrode gap is .166" wide. Those wise in the way of electrons have calculated that it takes around 13,000 volts to jump this gap. We need 10,000 to jump the gap on a cold spark plug. Add it all up and we have voltage to spare. As coil temperature can aggravate minor coil imperfections that normally wouldn't be a factor, the same test can be done on a warm engine. Engine quits while running? Hook the tester up in line with the spark plug and start the engine. When the engine quits, monitor the window. If spark is present, the problem is not in your ignition coil. By the way, this test stresses the coil well beyond the demand it would see in operation. Think about it. We're asking the coil to build enough voltage to jump TWO gaps - the tester as well as the plug. If your engine starts and runs OK cold and hot, you've got a healthy ignition coil.

Now, how about some of those old wives tales that just aren't true.

Rust on the flywheel magnets causes a loss of spark. Not true. A magnetic field does not care about rust. It has no effect on it.
A bright blue spark is best. A yellow/orange spark signifies weak ignition. Not true. Spark color determines virtually nothing. The hottest spark is ultraviolet which we can't see. Blue spark is cold in comparison to ultra-violet. Orange and yellow come from particles of sodium in the air ionizing in the high energy of the spark gap.
Laying the spark plug against the block and pulling the engine over can adequately test ignition coil output. Not true. The ignition coil will only generate enough output to jump the gap of the plug. When under compression, the plug requires twice the voltage to fire. This check is not an accurate test of the coil and can be misleading.
An armature air gap that is too wide will prevent spark. Not true. Well, sort of not true. Briggs & Stratton air gaps cannot be made too wide to prevent spark providing the coil is healthy and the engine is spun over fast enough. A wide air gap, say .030" will ever so slightly retard the ignition timing as the magnetic field takes longer to build within the coil windings."
Source

Not trying to be a smart azz, but, turn the ignition on! I have a newer Poland 20", and couldn't get it to start from the first try. I took it back to the saw shop, and the guy snapped the red ignition button up, and the saw started fine. I took it home and had to use a pair of pliars to get that darned red switch to move up, very hard to turn on. I suspect those switches are trouble prone!

LOL. I thought you were going to say " Take the Whole saw "--- and junk it ! Anyhow that's my thoughts.

I'm with the "did you try a different plug?" group. It's possible you got 2 bad ignitions, but it's not the most likely problem. Is the coil grounded well to the crankcase? Any frayed wires or sketchy connections? Solid state ignitions are pretty reliable, even Poulan.

Is the exhaust clear? I know you said it had been stored in a case, but is it possible that something got in there? I kicked and cussed a tiller once for days, then decided to tear the motor down, and when I removed the exhaust it was packed with a dirt dauber nest. Got all that out and it started right up.

For the record, I've tried about everything mentioned here. Different known good spark plug, disconnected the kill switch completely, etc. The whole saw is clean and in new condition 'cause it is basically new. I'd just used my Stihl MS170 a couple of days ago, so I switched spark plugs. The Stihl started right up on the plug that came out of the Poulan, and the plug out of the Stihl wouldn't fire in the Poulan.

I always keep coming back to a second defective coil/ignition module. Maybe I can find one from a different manufacturer.

I bought one of those Poulan 20" saws just recently. Used it once and a little 2" limb pinched the blade and threw the chain off. When I put the chain back on the sliders in the groove must have gotten bent and it wouldn't go in the slot in one place on the chain. Bought a new chain, but it takes a weird 72 tooth spacing. took it back and got the correct chain but the chain will not stay on. Next plan is to buy a new bar, but I was tired of messing with it so I bought a Stihl. I pinched it cutting a larger limb, no problem. I wasted my money on that "bargain" Poulan.

I have seen plugs on two strokes look clean and unfouled but change the plug and the bike starts right up. Gas fouled not oil fouled plug.

Goose---I have worked on two strokes for over 50 years and you might consider this----
Lubricate the cylinder wall, and make sure the clearance between the flywheel and coil is correct---app. 012. Proceed to spin the flywheel with an electric drill, at about 2,000 rpm, being sure rotation is in the right direction. C/C in most cases. Flywheel may have to be spun for a length of time but I had results within a few seconds from a DEAD coil.
I am fortinate enough that I have a Lathe and it is a simple matter to set the components up and run the procedure.
I had TWO dead coils and this worked on both and the saw has continued to work.
These modern day coils are complicated because many change the engine timing and also limit the maximum rpm.
Much better then a point type ignition because at 13,000 rpm there would be "floating" and other problems.
Good Luck--might work for you and it will cost nothing

No help for you Goose, but my Poulan is the only saw I can get to start reliably. Bought a couple of brands before that were supposed to be better, but couldn't get them to start every time. So they went back and got the cheaper and more reliable Poulan.

(quoted from post at 12:48:39 03/03/16) Goose---I have worked on two strokes for over 50 years and you might consider this----
Lubricate the cylinder wall, and make sure the clearance between the flywheel and coil is correct---app. 012. Proceed to spin the flywheel with an electric drill, at about 2,000 rpm, being sure rotation is in the right direction. C/C in most cases. Flywheel may have to be spun for a length of time but I had results within a few seconds from a DEAD coil.
I am fortinate enough that I have a Lathe and it is a simple matter to set the components up and run the procedure.
I had TWO dead coils and this worked on both and the saw has continued to work.
These modern day coils are complicated because many change the engine timing and also limit the maximum rpm.
Much better then a point type ignition because at 13,000 rpm there would be "floating" and other problems.
Good Luck--might work for you and it will cost nothing

Click to expand...

I've seen the same thing. My old reliable Sachs 116 would fire. Pulled the plug and spun it over with a 3/8 drill. Took about 10 seconds and I had a bright blue spark. I think it could be moisture or maybe some sort of corrosion within the pick up itself, but it works sometimes.