Cub not starting

[Rayman66]

1948 Cub won't start. New plugs, new wires, new points and condensor in J4 magneto; cleaned carb. Will backfire once or twice while trying to start but that is all.
Any help or advice greatly appreciated.
Thank you in advance.

 

[caterpillar guy]

Have you had the mag off the engine? IF so you may have it out by 180 degrees. Check gap, it is .020 for the points. IF not off are the plug wires on in the correct firing order. Check and change only one thing at a time to keep track of which one helps and which does not.

 

[rustred]

Backfiring is due to wrong timing. Whats the story here
on it. Sitting or overhauled it or when was it last running
? Is the firing order correct ? And was mag off?

 

[Rayman66]

(quoted from post at 19:27:04 11/08/23) Backfiring is due to wrong timing. Whats the story here
on it. Sitting or overhauled it or when was it last running
? Is the firing order correct ? And was mag off?

itting. Just bought it. Somewhere around 3 years since last ran. Firing order correct. Had mag off and installed new points and condenser.

 

[teddy52food]

Points should be .012 to .015. If the gap is too wide, they may not close.

 

[rustred]

Then u need to recheck the timing as thats ur problem.
Get number 1 on compression at tdc. Then pull the dist
cap and look if the rotor is pointing to number one spark
plug.

 

[wore out]

Did anyone get into the wrong area and mess up the rotor timing, either now or previously?

You can see the timing marks on the rotor and pinion gear in the photo above.

 

[Rayman66]

(quoted from post at 20:12:27 11/08/23)

Did anyone get into the wrong area and mess up the rotor timing, either now or previously?

You can see the timing marks on the rotor and pinion gear in the photo above.

ade sure to stay out of that area and tractor did run about 3 years ago.

 

[used red MN]

I looked back at some of your other posts trying to get a feel of your knowledge level concerning ignition timing. I want to make sure you understand some things about this. Rustred said get it on TDC of compression, that means the compression stroke of the piston. This means it has to have both valves closed to push air out or build pressure against your thumb and then the piston is brought to the top and the timing marks aligned for timing your mag. Every other time the piston comes to the top of the cylinder it is on the exhaust stroke. It will not push pressure on your thumb on that stroke because the exhaust valve is open. The last thing to be clear on is to make sure the number one piston can pump compression. Do that by pulling the plugs and cranking it over a couple time to make sure it will build pressure against your thumb. Valves can stick on engines that set for a time. Be a good idea to pull all the plugs and check for some amount of compression in all of them. That way you know if that is an obstacle keeping it from starting as well. You have a manual for this tractor? If not go to Farmallcub.c.. I bet you find one there.

 

[grandpa Love]

Timing is off. I see you removed the mag
to install points. I'm betting you need to
check your timing. A magneto on a Cub is
very simple to time, BUT also very easy to
install 180 out. We have installed and
timed dozens of magnetos. Call if you want
some advice, tips, tricks. One very easy
test to see if you are 180 out in move the
plug wires 1 spot clockwise on the
distributor cap, still won't start? Move
one more spot, now you are 180 out , or
correct! It might surprise you how fast
it starts! 256-4zero4-zero123. Kevin

 

[Rayman66]

. Have tried all of your suggestions. Still won t start.
Had backfire out of carburetor and exhaust at same time or very close.
Thank you for your help.