Lawn Boy 5239g, no spark no matter what I try!

[peteclark3]

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. :-(

 

[Eugbug]

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. :-(

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).

 

[peteclark3]

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

 

[KennyV]

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

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

 

[Eugbug]

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

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.