Please help! MTD 1846 YardMan won't roll over...I have a video of what it's doing

Welcome to MLF!
Thanks for the video, it really helps to almost be there.
I know its new but does the battery have a full charge on it?
Also you need to see if you are getting spark at the plug.
If you are, then you need to see if you are getting gas, Have you checked the fuel level?
What concerns me is the smoke event during the jump start. If the hubby over did it on the jump start he could of toasted the starter. you shouldn't crank it too long if the engine does not start
The initial problem could be junk in the carb from sitting (how long did it sit since its last run?)
Now compounded with a dead battery (Initially), you could have a couple of issues.
Check the simple things first before ripping everything apart.

From the video, it looks like you have a 275 amp battery. On a twin i would recommend a 350 amp battery. Instead of jumping it from car battery to tractor battery, jump straight to the tractor starter. Of course make sure your cables are hooked up correct. What smoked is the critical factor here. That would go a long way to getting to the root of the problem.

Definitely needs a 350amp battery, these engines were known for needing the most available battery, to crank over.

These also suffered from carbon build up on the pistons and heads and briggs recommended periodically removing the heads and using a plastic scraper to remove carbon buildup, the buildup can get so bad that it causes excessive compression, and hard starting.

The last thing...smoke, once you let it out you can never get it all back in, so its important to figure out exactly what smoked, and why...and fix that as well.

Definitely needs a 350amp battery and models with overhead valves can cause hard starting or not start at all because the valves need adjustment. Not sure if yours has them or not. If it does this might be your problem.

RED-85-Z51 said:

These also suffered from carbon build up on the pistons and heads and briggs recommended periodically removing the heads and using a plastic scraper to remove carbon buildup, the buildup can get so bad that it causes excessive compression, and hard starting.

Click to expand...

I think Briggs recommends decarbon every 50 hours, which seems excessive. I have had them in here knocking pretty bad, pull the head and find so much carbon the piston is virtually hitting the top of the head, carbon to carbon of course. That will cause extremely high compression and hard starting.