magneto help

Fri Dec 13, 2013 10:59 pm

Im sure its been addressed but im new to the site. My cub quit. I found the coil out of resistance range in the mag. New coil and while I was there, points and condeser. Runs good now. I know how the manual says to time mag to engine. I measured out pulley and set with magneto timing light. My questions is the degrees btdc. I have found everything from 13 to 20. Mine starts at 13 ok. Starts better at 18. More power at 23btdc. I wonder where everyones having the best luck. I figure I will have troubles starting that far advanced this summer, but for now running smooth?

Re: magneto help

Sat Dec 14, 2013 12:28 am

this is a tricky question when it comes to magnetos. I have found after rebuilding cubs for almost 40 year that i prefere to time all my cubs by ear especially the cubs with battery ignition. I do so with the magneto also but only can do so much with the mag timing. My self i adjust tihe timing to where its is runnng as far advanced as possible and still start well. You are correct. the further advanced you can run a engine the more power it will put out to a point. I would say that you having it set at about 18 deg is pretty good. If advanced tooo far the valves will ping under a load. that is a indication to back off some. My 76 mowing cub has a battery ignition. with 5 ft woods mower. I time it under a load running the mower at high idle (2600) RPM. I beleive it is advanced about 23 degrees and has alot of power. I have run it at 26 degrees advanced but valves had a slight ping and also i had a over heating issue. backed it off to 23 and no issues. I assume you cub since it has a mag is a little older and doent have the big manifold and zeneth carb with the later cam so you my not be able advance it to 23 without pinging and other issues.

Re: magneto help

Sat Dec 14, 2013 12:44 am

Thanks a lot for the reply. Yes I believe I have a 1950. Have not looked up numbers yet but has a J4 mag. Glad to hear someone else set at 23. After messing with it tonight it seems the smoothest at that setting.I have snow plow on right now. Will know tommorrow when put under a load.

Re: magneto help

Sat Dec 14, 2013 5:48 am

To time a mag set the engine at TDC on number one cylinder. Check that the timing marks line up. Loosen the mag and rotate it towards the engine until it hits the side of the block. Turn the engine one revolution back to the timing mark. Rotate the mag away from the engine until you hear the impulse click. Tighten down the mag and its in time.

Re: magneto help

Sat Dec 14, 2013 6:06 am

Welcome to the forum from Arkansas. Lots of information compiled on here thanks to a lot of the folks that have contributed so unselfishly over they years.

Re: magneto help

Sat Dec 14, 2013 3:32 pm

Clark Thompson wrote: I have found after rebuilding cubs for almost 40 year that i prefere to time all my cubs by ear especially the cubs with battery ignition. .


I timed my 1961 Cub by ear a couple weeks ago and the increased power was more than noticeable. It has battery ignition. It would not pull itself up an extremely steep hill even in first gear before adjusting the timing. Now it will easily climb the same hill in second gear. The crank pulley has been broken and welded. Which completely obscured the timing marks. I will need to make new timing marks or change the pulley before I can see where I have it timed.