1950 Cub with J4 mag

[jtrdad]

Hello everyone I just joined and have learned alot about cubs. I have inherited a 1950 cub with a J4 mag from my late father in law. It had been sitting in a garage for about five years after it cut out in the field. I have changed the oil. and fuel. I wasn't getting any spark out of the mag. I have put new points, condenser and a coil and timed it after viewing the video on here. getting backfire through the exhaust pipe now and have no clue what to do. Can it be a timing issue? I gapped the points at .013 I think I read that here but should it be .020?
Any help would be appreciated, I really want to get this running for my wife, it's been in the family as long as she can remember.
thanks
Jerry

[Eugene]

Welcome.

First thing - - PRIME THE OIL PUMP before you fire up the engine.

Search function, top of page. Search for Video Magneto Timing. There are several posts on the topic and a how to video.

[ShineOn]

Howdy Neighbor ,

1949 w / J-4 here . Just went through its ignition system last week . 0.20 it is . Static timed per local instructions and runs like a top . Cut about 2 acres of 7-8 foot thick overgrown pasture in one pass and didn't miss a beat .

Lovely machine to work with .

Good Luck on getting you'rs up to top snuff .

[Eugene]

Magneto point gap .013.

[ShineOn]

Magneto point gap .013.

Hummm . . . Better double check my source . The 49 measured about 0.18 when I pulled it to check things out . Starts and runs a champ .

[Cecil]

If you are backfiring I would think that you are 180 degrees out of time. It's real easy to do when you reinstall the mag. Get the engine to number 1 TDC and see where the rotor is pointing.

[Glen]

Hi,
Here is a page from a Cub owner's manual showing the magneto points and the gap, which it says is .013 inch. .020 inch is the gap for a Battery Ignition Unit points. Click on the pic makes it bigger.

http://www.cleancomputes.com/Cub/Cub%20 ... age-28.jpg

[ShineOn]

Hummm . . . My notes say  F-4 and F-6 = 0.013 J-4 = 0.020 .

I've worked on a number of mags over the years and .020 is pretty common setting . Wonder if the mix-up / conflict is in the J-4 sharing parts with battery setups ? I wouldn't contradict the manual page however .

[dgrapes59]

Welcome to the Forum!

Congratulations on obtaining your FIRST Cub, good luck getting it going,

[John *.?-!.* cub owner]

If you crank it by hand do you hear the mag impulse trip twice per each round of the crank? Check if spark will jump from center wire coming from top cover of mag. If no, disconnect kill switch on side of mag. If still no, most likely a bad coil.

[Mag Man]

OK Have not been here in a long time but Yes it is .13 thousands for a mag, Here is what you need to know your #1 cyl will be up TDC on 2 dif strokes, So you thought you had it and its probably 180 off or what ever, Either completely change the plug wires on the cap 180 or take plug out of #1 and while you turn it over with coil wire out of mag Feel for compression on your finger for compression stroke,Should blow good on finger other wise you will have It up on Exauste stroke or what ever it is and you will be 180 off . If you change the plug wires around and it starts and runs then you will either have to take it off and retime it or let anyone that will ever use it know that so there is no discrepancy later on, lol Other wise did you by any chance screw up the rotor timming? When you took it apart that needs to be timed also, Or maybe you are just a cyl or 2 off when installing but probly 180 off I even do it sometimes and I have installed many many mags, lol

[Rudi]

Now there is a voice from the past .. how you doing Jon? Jon is a real pro at mags as is Cecil. Pay attention to their advice. They are usually bang on

Directly from the GSS-1012 - Electrical Equipment - Page 03



If you are backfiring and it is timed to #1 TDC as Cecil said you are 180 degrees out.

John provided this pic to show where the governor should be when you re-install the mag

this is the position of the governor to magneto drive slot with the engine at TDC of any cylinder.

[BIGHOSS]

Someone posted a few weeks ago about using a cork in the no. 1 spark plug hole to check for TDC. I am here to tell you that it works great! Get ready to look for the cork in your shop, as it pops out pretty good. I found that you want to just snug the cork in the hole, because too tight will not work as well. Good tip when working alone.

[jtrdad]

Thanks to everyone who took the time to reply, I must say I am impressed by the amount of feedback I received. Just got in from work so tonight I will be trying to get this timing correct. will be posting results

[Mag Man]

I AM DOING A BIT BETTER RUDI, Just had my last 8 teeth removed in the last 10 days last fri was the last 3 surgical, Now they are all gone along with the infections. And I will have to wait 3 months or what ever and try to afford some new ones. Then 1 to 3 more back surgerys and I may be on a track of being a whole person again.Depending on what they can do with the minimal invasive procedures, I will not let them open me up 6 to 8" again for nothing.!! The last 5 to 6 years have been real rough for me. But Hopefully it will get better.