Cub Magneto Timing

[WayneMo]

My cub ran all summer but will not start with this recent cold snap. It trys to start if I choke it first and then open it a little but seems to kick back a occasionally which sounds to me like it is advanced too far. I am hand cranking it with no battery just the magneto.
I get good gas flow and the carb jet is clean. I installed the magneto this summer according to static timing instructions and it seemed to start and run ok.
Can I just loosened the mag hold down bolt and rotate the mag just a bit to retard the timing? Should I rotate it CCW or CC to retard it viewed from the rear of the tractor?
I plan to keep it running on the magneto and no battery if I can.

 

[old]

If it has battery start use it. My Cub is battery powered all the way but doesn't have a working charging system and battery last for a very long time with out even needing to be charged

 

[rustred]

here is a tid bit... when you rotate the magneto or distributor in the direction the rotor turns that is retarding the timing. when you want to advance timing u turn opposite of roto rotation.

 

[Jim Becker]

rustred (quoted from post at 20:50:22 11/12/21): "here is a tid bit... when you rotate the magneto or distributor in the direction the rotor turns that is retarding the timing. when you want to advance timing u turn opposite of roto rotation."

Except the Cub magneto, like many others, has a 2:1 gear reduction that also changes the direction of rotation. To retard the spark, you rotate it CCW when viewed from the back. In other words, to retard you push the top of the magneto towards the engine block.

 

[gene bender]

when you remove one of the wires and put a spark plug on that wire grounding the plug what kind of spark do you get. Removing the cap when the rotor fires is the rotor on the tower when it fires you mite have the rotor out of time. Does the engine start when you pull the tractor

 

[grandpa Love]

If it was running fine, how did the timing get off? If you have a battery available and starter on it use jumper cables to start it. See how it runs. After 100 tries at hand cranking spark plugs are wet with gas, making it harder to start. Or if you have help , pull it around in 3rd gear to start. If it sat a while points may need a quick file and clean. But yes, to answer your question, you can loosen the mag and turn it a bit. Try both directions...... Find the sweet spot

 

[WayneMo]

Thanks for all the expert help.....this forum is the greatest.
I don't see how the timing could have chnged but I will try to tweak it. I bet the plugs just got wet cranking it by hand.

 

[WayneMo]

I used to set the timing on autos at about 5 Degrees advance. I don't
know what would be good for the mag and cub. Sounds like the static
timing sets it at TDC.
Also do not know if hand cranking would require a different advance
viewing the timing marks on the pulley than a starter motor would like.

 

[rustred]

why guess, just get the engine on TDC on compression. then put a piece of thin paper inbetween the points. then you turn the mag so you are going opposite way of rotor rotation. as soon as the paper will pull out you are statically timed.

 

[jimtrs]

(quoted from post at 20:34:49 11/12/21) .....I am hand cranking it with no battery just the magneto......
I plan to keep it running on the magneto and no battery if I can.

For the safety of your hand, wrist, elbow and arm, do not advance the static timing [b:214f725add][i:214f725add]before[/i:214f725add][/b:214f725add] TDC for hand starting. If the engine does not start when timed correctly, you have other problems.

Set static timing @TDC, then double check. Rotate the engine slowly with the hand crank. The mag should trip exactly when the 2nd notch on your crank pulley comes in line with the pointer.

For safety of hand starting, @ TDC. A hair late is better than too early.

This post was edited by jimtrs on 11/13/2021 at 03:16 pm.

 

[Janicholson]

If there is humidity in the area and condensation on metal, the cap may have moisture in it directing good spark to wrong places. Jim

 

[teddy52food]

1st mark it so you can put it back where it belongs while you look for the real problem.

 

[jimtrs]

(quoted from post at 14:57:30 11/15/21) 1st mark it so you can put it back where it belongs while you look for the real problem.

Cub crankshaftshaft pulleys that have 2 notches were used on engines with distributors. Though over the years, pulleys or mags / distributors have been swapped around. The first notch is used for advance timing with a timing light.

If you have a mag with a 2 notch pulley, static time the mag to the second notch (TDC). If you have a distributor, you can either static time to the 2nd notch, or better yet, advance time at no load, high rpm's to the first notch (16 degrees btdc)