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Hey folks! I've been trying to fix our Lawn Boy 5239g's "no spark" problem for weeks (the weeks are mainly waiting for new parts to come). Tried spark plugs that work in other mowers (same plug type), it has a new condenser as of today, new points, and even a new magneto (coil?)

No matter what I do, I can't get this thing to spark any more. I'm not sure what might have caused the problem originally.

I'm attaching pictures of the top, hoping something is obvious.. if not, do you have any ideas of what I can try next, or how to troubleshoot?

First check the gap on points then take avolt amp meter contintinuity setting to make sure when points open there not a short to armature plate. Make the spark plug wire is in coil. Recheck gap between coil and flywheel magnet .010. Just make sure there is not a path to armature plate when points are open.

Thank you! I apologize but just to make sure I'm doing it right, where should I touch on the mower with the multimeter to see if there is continuity?

The points in the system complete the path to ground, for the primary side of the coil... when the points are open there should be no path to ground... (aside from the charging of the condenser) ... :smile:KennyV

Could I be so bothersome as to ask where to touch the two ends of the multimeter wires with the points open to test this?

Across the Open point set... But you will be reading the LC of the primary & the capacitance of the condenser.... Your main concern would be that there is not a short, (very low resistance), when the points open... :smile:KennyV

Check your wire connects at the point make sure theyre not touching the armature plate. Some times when you tighten that nut sometimes they twist around touch the plate. dicsconnect wire to kill switch to see if a problem. Hang in there buddy we get that LB running if takes till doomsday. If everything checks out fine with ignition there is couple of other areas consiter.

Thank you.. This lawn boy was a gift from Santa for my son (8yo) two Christmases ago.. Was running great until just recently! Before I replaced the coil and condenser i had put elec tape on the wires so the connectors wouldn't touch the plate, and watched for that when I screwed the new condenser bolt on. I will check again, but after that what should I try next? If I can find out what two places to touch with the multimeter to check for a short, I can probably ask better questions if I can see what might be shorting it.

Thank you again!!
Pete

Oh ok, I missed the second to last response. So I open the points and I touch the wires one to each point, and if there is continuity that is bad? Or is that expected?

I apologize, as soon as things get into electrical terms, I'm pretty stupid..

You will be measuring the primary windings of the coil plus the condenser that is wired parallel to it.. It will have some resistance, not a dead short... if it is almost the same as when the points are closed, you have something shorted in your wiring Or your condenser is shorted or the points are Not opening.... :smile:KennyV

I need instructions like you'd explain to a 4 year old... this is my multimeter (it's similar to this)..

http://www.tennesseequipment.com/East-Cost-/Maine-/Agencies-/Craftsman-multimeter-82362-pix.jpg

Instructions like.. touch the red here, touch the black there, and if you see X on the dial, you've got a problem.

I'm a software developer and understand that instructions like this might not be possible, but if it is, then it would definitely help!

Thank you all again for your patience!
:confused2:

1) Set the mutimeter to measure resistance (ohms).

2) Put the black wire onto the grounded side of the points. The red wire goes onto the other side.

3) When the points are open, there should be significant resistance shown on the meter. When the points are closed, there should be no resistance shown on the meter (confirming that the points work.)

Hey buddy how was your luck today?

Might have found something.. If I am reading the meter right I might have resistance when the points are closed too. I made a video, hopefully it will be easier to help me with this!

http://www.youtube.com/watch?v=azFwxJgvcPA

peteclark3 said:

Might have found something.. If I am reading the meter right I might have resistance when the points are closed too. I made a video, hopefully it will be easier to help me with this!

5239g won't spark - YouTube

Click to expand...

I watched the video but I couldn't tell for sure where you were putting the red wire. The black wire was grounded -- right?

If you have any resistance when the points are closed that's a big problem. Are the points actually making contact? Could there be some dirt or other insulating stuff between them?

When I re tested, it seemed like I have no resistance no matter if the points are open or closed.

What should I touch the black wire to, to ground it?

And where should I actually be touching the red wire to?

Pete

peteclark3 said:

When I re tested, it seemed like I have no resistance no matter if the points are open or closed.

What should I touch the black wire to, to ground it?

And where should I actually be touching the red wire to?

Pete

Click to expand...

The black wire could be attached to any metal part of the engine -- you could hook it on with an alligator clip if you have one. The side of the points that does not move when the engine turns is the grounded side.

The red wire goes onto the side of the points where spring connecting the condenser is attached (the side of the points that moves) -- that wire is part of the primary circuit.

If you have no resistance then there may be a short in the primary circuit.

You to remove your advane timing cam see better what you are doing.

Darn, I thought I had it. To check for a short to ground with the points open, I disconnected the two wires and the points spring from the condenser. The points spring and the wire to the switch didn't have a short to ground, but the wire to the coil did. So I figured maybe it was the white short wire (in the picture) coming out of the coil being connected to one of the screws holding the coil down causing the problem. The old coil (I just got this new one) had the short wire like this, when it was running fine, so I just did the same thing with this new one. Once I disconnected the wire from the screw holding down the coil (as in the picture), I no longer had a short to ground when the points were open. This was what I thought was the "a ha!" moment. Still, once I reassembled everything (for now I just wrapped elec tape around the contact on the short wire), and cranked it, I got no spark.

Now I gotta go tell my son; he came in to watch mower vides on youtube.

Sorry about all this guys but I really appreciate your help! What can I do next? Or, did I do everything totally wrong above?

Pete:confused2:

The circuit diagram below is for an ignition system which uses points (non electronic or CDI).
When the current through the magneto primary is at its max, the points open, the magnetic field collapses and you get a high voltage pulse from the secondary which produces the spark at the plug.
You have replaced the condenser(capacitor) and magneto so the chances are these parts are OK.
Check everything is grounded ok. The capacitor is grounded by the clip which holds it. The primary and secondary of the magneto are grounded by the lead coming from the coil in your photo which goes to the left mounting screw for the magneto. One side of the points should be grounded also.
Check the kill switch isn't shorting everything out. From what I can see in the photo, the connecting wire to these is probably the lead coming from the capacitor and disappearing down into the hole. One end of the kill switch is grounded.
As all the other posters suggest, measure the resistance across the points. This should be low and become lower as the points close. It is possible the points aren't adjusted properly and not even closing properly. Often the position of the capacitor is adjusted to give the correct points gap and then the spring on the points properly closed.

Ok, thanks. First, I'm going to get a new digital multimeter at home depot, because I feel like I can't get a consistent reading with what I have. Very hard to follow the needle.

Do you have any idea what the resistance should be (the reading on the multmeter.. roughly?) when the points are open/closed?

Also, should I have NO continuity between the points when they are open? Or still some continuity, just with more resistance? I ask because what I'm struggling with when trying to use the multimeter is figuring out why there shouldn't be continuity when I touch the black to the ground and the red to the side of the points that opens, when the points are open. It seems that everything in there is metal, and everything seems to touch everything else at some point, why wouldn't there be continuity?

Thanks again. :-(

peteclark3 said:

Ok, thanks. First, I'm going to get a new digital multimeter at home depot, because I feel like I can't get a consistent reading with what I have. Very hard to follow the needle.

Do you have any idea what the resistance should be (the reading on the multmeter.. roughly?) when the points are open/closed?

Also, should I have NO continuity between the points when they are open? Or still some continuity, just with more resistance? I ask because what I'm struggling with when trying to use the multimeter is figuring out why there shouldn't be continuity when I touch the black to the ground and the red to the side of the points that opens, when the points are open. It seems that everything in there is metal, and everything seems to touch everything else at some point, why wouldn't there be continuity?

Thanks again. :-(

Click to expand...

Disconnect the white lead from the mounting screw on the magneto. As far as I can see, this is the ground lead. This will "float" the magneto winding. With the points open, there should be infinite resistance and a near short circuit when they close. Infinite resistance on a digital meter is usually indicated by a "1" on the far left. If the resistance isn't infinite, something is causing a short. Possibly the kill switch or the connecting wire to it. If the resistance isn't very low when the points close, then they aren't making proper contact on closure and need to be adjusted, probably by the screw holding them.
Re-connect the white lead. With the multimeter set to the lowest ohm range, touch the two probes together. The resistance measured is likely to be about 0.5 ohms (you are just measuring the resistance of the leads).
With the points closed, the resistance will probably be slightly above this, maybe 0.6 or 0.7 ohms.
With the points open, you are measuring the resistance of the primary which would be about 1 or 2 ohms. The capacitor behaves as an open circuit (see the diagram in the first post I made).

SUCCESS!! It was the points gap.. I had them opening too far. I didn't think it mattered if they opened too far.. I guess it does! Would anyone be willing to explain why the points opening too far would cause this? Just want to learn as much as I can.

Here it is running!
http://www.youtube.com/watch?v=w85wxZTaHs8

Thanks to everyone for all of your help!!!

Pete

peteclark3 said:

...why the points opening too far would cause this?

Click to expand...

Glad you have it running...
As Eugbug, 'pointed' out before... the ignition fires when the points Open, when the coil charge collapses the secondary of the coil is excited & produces the high voltage for the spark plug...
If the points open too far... either the points will Not close long enough, or at all, preventing the primary from 'charging' or the timing will be off. For things to work properly the points have to remain closed an adequate number of degrees of rotation ... if they are gaped too wide they will not be closed long enough.... or they will fail to close tight enough to close the circuit.... :smile:KennyV

peteclark3 said:

SUCCESS!! It was the points gap.. I had them opening too far. I didn't think it mattered if they opened too far.. I guess it does! Would anyone be willing to explain why the points opening too far would cause this? Just want to learn as much as I can.

Here it is running!
5239g is running!! - YouTube

Thanks to everyone for all of your help!!!

Pete

Click to expand...

Glad you got it working! Its very reassuring and rewarding when a machine springs into life which has been doing your head in trying to fix!
I agree with Kenny about the points. The chances are they probably were too far open and may not have closed once the cam moved off them or opening prematurely affecting the timing. Another thing to watch for on an old machine is oil leaking from an oil seal where the shaft exits the engine. This would be more common on a horizontal crankshaft engine where the flywheel is at the side. Oil can drip onto the points, fouling them and preventing the thing from starting.