New cub owner ignition questions

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sidschopshop

New member
Hello I am wanting some insight on an ignition problem I’m having with my 1948 cub. The cub is new to me, looks like it has a the magneto disabled and a 12v battery going to a coil to power the ignition.

The tractor ran great then started having an ignition miss. I bought a tune up kit and upon disassembly and following the IH manual, at TDC I noticed the rotor wasn’t in its correct spot (#1 was pointing sideways toward me) so I took note going forward. Replaced the condenser and points this is where I am getting confused. The manual states not to turn the motor with the distributor body off but I needed to set the points gap to .013 so I turned the crank maybe 1/8 turn to get onto the cam. Going back to the rotor, the old timing lines weren’t correct looked like 2 or 3 teeth off but thought I’d better install the new one lined up. I installed the new cap with the plug wires installed in the correct firing order but one terminal off.

With all this done the tractor does start and run but still has the miss which seems to have gotten worse, and lacks some power on taking off in 3rd gear. Do you think simce I turned the crank to set points my magneto isn’t timed that this has affected the timing/governor? Also since I’m using a battery ignition on a magneto driven points, does the gap still need to be .013 for does it need to be .020? Next things I’m going to try are some mystery oil and new plugs. Thank you
 

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Gap should be .020 if i remember correctly. are you still positive ground or has it been converted to negative ground? Here's a video for timing the magneto-

For the power issue and miss, it may be from the valves-have you adjusted them yet? Mine would stall in 3rd and struggle doing work like running a disc while in 2nd. Valve adjustment resolved that issue.
jk
 
I guess the picture is from before you lined up the timing marks. You need to set the points to 0.013 even if you are using an external coil. Any different gap will effectively change the lag angle (the advance while running). Turning the engine a small amount as you did is unlikely to cause a problem. The fact you have since started it confirms no large timing problem. Agree on checking the valve adjustments. Double check the plug wires for the right firing sequence, 1 3 4 2 (clockwise around the distributor cap). Plug wires should be solid core, not resistance type. Check their condition and the condition of the plugs.
 
sidschopshop said:
The manual states not to turn the motor with the distributor body off but I needed to set the points gap to .013 so I turned the crank maybe 1/8 turn to get onto the cam.
Click to expand...
Hi,
Sometimes when putting in new points, you have to turn the engine slightly to get the point on the highest part of the cam. If you do, watch carefully how far you have turned the engine, and turn the rotor the same way, so you don't lose the timing of the cover to the magneto.

The timing marks on the rotor and it's drive gear should be aligned with the cover off.
Clean the area by the gears, and put in new grease on the gears, the Cub owner's manual says to grease them.
The engine should run right with the spark plug wires in the original positions, number 1 spark plug wire is at the top hole of the cap.
You can use a timing light on the engine, when it's running at slow idle speed, about 500 RPM.
Any time the magneto isn't making the snapping sound, the timing should be about 13 degrees BTDC. That makes the mark on the engine front pulley about 3/8" - 1/2" before the TDC mark.
If the pulley has 1 mark it should be the TDC mark.
Below is a page from the 1950 Cub owner's manual telling how to time the magneto to the engine.
You have to take it off to do what it says at the beginning.
Using the timing light is easier if you just want to check it, or adjust it, since the engine runs. :)
https://farmallcub.club/rudi/farmallcub.com/rudi_cub/www.cleancomputes.com/Cub/Cub Owner's Manuals/McCormick Farmall Cub Owner's Manual 1950/Page 32.jpg
 
Thanks for replies. I did line up the rotor and new grease when I reinstalled. Haven’t hooked a timing light up yet but will be interesting to see what it shows. With the #1 cylinder at TDC the rotor points to where the #3 plug should be. I have a new set of hot plugs to try. I could see the valves needing adjustment as you guys have mentioned as well. Been really enjoying working on this little tractor. Thanks
 
Check the valves clearance as stated .015, and do a compression test, wet and dry to see if you have good compression. Weak compression on a 78 year old engine is a very real possibility. So if that's the case you will have to fix the problem or live with for now. JMHO Stan
 
Hi,
If the Cub engine smokes, with blue smoke, it could have stuck piston rings, a common thing on Cubs.
They have said on here to use Seafoam in the engine oil, it can help loosen stuck piston rings.
One of the experts on here said to use it for 2 oil change periods.
The 1950 Cub owner's manual says to change the oil every 120 hours of use.
They have said on here Seafoam can help increase compression also, if the compression is low because of stuck rings.
If the rings are wornout, the Seafoam won't do much.
I remember reading on here people saying they had good results using it. :)
 
NO blue smoke which is good! Im thinking this tractor hadn't seen much use in a while and maybe since the little I've owned it some deposits are getting loosened up. I will do another oil change and add some seafoam. Thank you
 
New set of D21 plugs fixed the erratic miss that I was chasing. Still might be a little underpowered mainly notice it trying 3rd gear in grass. Even so the tractor runs great now, I will use some seafoam in the tank next time I get to the parts store. I will also post some a photos of the tractor for you all to enjoy. Thanks again
 
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