I have an Ariens 24" snow blower with a Briggs and Stratton 205cc engine.I'd like to check the spark plug, but need to see an engine schematic so that I know where it is.

If it is new, contact your seller for support under warranty
https://www.briggsandstratton.com/eu/en_gb/support/faqs/browse/engine-problem-solving-tips.html

To start, it needs fuel, air and spark, start by checking if you have all 3

Cam timing requires engine disassembly on small engines and it's either right or wrong.
You could be off on ignition timing if you sheared the key on the flywheel which then requires the flywheel to be removed to replace the key.
Make sure it's not something simple before you go deeper into the problem. Gas/fuel delivery, dirty carb, bad spark plug, all the safeties not made.

it is prob a 13/16 this is the most common most of the time you cannot get a wrench on a plug but a socket , if it is smaller then it is a 5/8 lefty loosie righty tighty do not over tighten the plug

The usual cause for the problem you describe is related to fuel/
carburetion. Today's formulation of gasolines have a shelf life of only 4-6 months before they start gumming carburetor. Other forms of fuel contamination (dirt, water, etc) may also be the culprit. First step is to remove and thoroughly clean both the tank and carburetor. Reinstall. Install a small engine filter in the gas line when you reassemble. Use FRESH gasoline after you are ready to start your engine.

Down load it

I have attached a link to an article and video that will help you be able to change your spark plug. It is very easy to do and a quick fix that solves many engine problems. I hope it will help you accomplish what you would like to do!

These step by step instructions will have your spark plug swap done in no time!

Best of luck!

Changing the Spark Plug on an Ariens Two Stage Snow Blower

Some times, the seals not sealed yet not being run. Check all your oil and gear oil levels and run it. Hope everything will be ok then.

I am assuming this is a 22 or 24 inch model. The engine is an overhead valve design and the spark plug is buried on the left side of the motor (looking at it from the handles) You should be able to see a large black wire going into the engine. Depending on the engine make it may have a rubber cover or just plug wire covering the plug.
On this page are pictures showing the location of the spark plugs on Briggs & Stratton engines.
http://www.briggsandstratton.com/engines/support/frequently-asked-questions/Identifying%20the%20correct%20spark%20plug%20and%20gap.aspx
The OHV horizontal shaft engines are about half-way down the page.
Feel free to ask any other questions. I know Craftsman Snow Blowers. Please remember to rate this answer!

other than timing I would make sure the plug you are using is good

Check engine oil.

Remove wire from low oil sensor and the start.

Replace low oil sensor.

Hope this tip help solve your problem.

r/David