This has me stumped.
 

You may or may not recall but a little over a year ago I did an engine swap in my 782. I swapped in an M20 from a Huskee. Before the swap the M20 started having a spark issue, so while I had it out I replaced the coil and starter.
It's been hard to start ever since and has little and intermittent spark. (yes I have a spark tester)

Several times in the last few months I have hooked the spark tester to one spark plug and have no spark or intermittent spark. I found if I take the air cleaner off and put my gloved hand over the intake it gets what looks like normal spark. So I put the plug wire back on and do the same thing and it starts.

Question is, how does that affect the spark? Once it starts it runs great.:bash2:

You might have a plug wire that intermittently shorts to ground. I would suggest, that you look at the plug wire(s) real good and see if there is any frayed spots. Let us know what you find.

Isn't the wiring different for the M20 on the 782?

Cub Cadet 123

Yes. One has to make modifications.

Recently, another member Diesel Doctor had a Mag twin that was running badly. He rebuilt the entire engine and it still ran poorly. Finally, I believe, he replaced the coil...again...and it runs very well now.

The new coil came with the spark plug wires attached so they should be good.
Yes I had to do the relay mod for the M20. I just don't understand how cutting off the air to the engine has any affect on the spark.

I know it's hard to believe but I tried it several times to make sure I was seeing things right.

Once it starts it runs good, That's whats got me baffled. Seems if the coil was bad it wouldn't run so well.
You have to pull the engine to get to the coil, so I'm not looking forward to doing that.

Have you changed the spark plugs? Are they the correct ones for that engine?Have you checked the choke cable linkage to see if the choke plate is closing completely?:bigthink: Please don't misunderstand...I am not being condescending...but you have not mentioned anything about these simple items. :beerchug:

Yes I put new correct spark plugs in when I did the swap. The choke is closing all the way but the choke plate has like a quarter inch hole in the middle of it so it doesn't shut the air completely off. When I put my hand over it and shut all air off is when it gets spark.
I know, sounds strange but that's what it's doing. Since I found this method, at least I can get it started when needed.

Did you set the air gap @ approx .010 on the new coil?
Now as far as starting with your hand over the carb.
You are doing 2 things:
#1 increasing the richness of the incoming charge.
#2, decreasing the compression pressure by restricting the amount of air entering the cylinder.
That makes it easier to ignite the mixture with a weaker spark.

It is not unheard of to get a bad new coil, I understand your not wanting to spend 30 minutes removing the engine to get at the coil to replace it.
As a test:
Decrease the spark plug gap to .020 and see if it helps starting.
If it does, it reaffirms the idea that it is ignition related.
Also, remove the white magneto kill wire plug @ the connection closest to the coil and see if that helps.
I've seen them shorted, or shorted @ the Ign. switch.
lets us know what you find.
Edit,
I've also seen aftermarket coils that do not produce spark at less than optimal cranking speed.

Maybe his hand is creating a better ground for the engine, is your engine properly grounded?
Stand on a wooden piece of wood and see if it does the same.