Small Engines (Lawn Mowers, etc.): mower engine cuts out under load

Question
QUESTION: The mower: Montgomery Wards riding mower model# TMO-33551A A2540. The motor: Briggs and Stratton 18 hp. The problem:The engine starts up and then will idle fine forever at both low idle or high idle. But when I engage it in gear and the engine is under load, it dies within about 15 seconds. I have just acquired this mower and I changed the motor oil, the gear oil, checked the plugs(they look okay)and lubed the steering parts and levers. Is it likely that this is simply an air/fuel mixture problem? If so, do I need to remove the front of the mower to access the carburetor? Or is it likely to be some other issue? Thanks for any help.

ANSWER: Does the engine die when you engage the blades with the transaxle in neutral?

Is the engine an L-head opposed twin cylinder style?

It is possible the carburetor is dirty, on the high speed circuit as the throttle butterfly opens up when the engine is loaded and the high speed circuit delivers more fuel.

Do you have an air compressor?

Eric

---------- FOLLOW-UP ----------

QUESTION: The engine will run in gear for about 15-30 seconds, with or without the mower engaged. Idling in neutral, it just keeps running, no problems. As for the engine, it is a twin cylinder. L style? I'm not sure, the images I see on a google search are varied so I am not certain. And yes, I do have a compressor.

ANSWER: The first step I would take is to see if the issue is fuel or ignition.  

Does the mower start right back up after it stops if you put it back in neutral?

Eric

---------- FOLLOW-UP ----------

QUESTION: Yes, the mower will restart after cutting out, although the interesting thing is that restarting it seems to require me to close the choke, then open it fully as I am cranking the starter. So, a lot of the similar questions I have found on the web about this seem to be answered with "needs a valve adjustment".  Do you think that is a likely culprit?

Answer
I would start by rebuilding and cleaning the entire fuel system, new fuel filter and a carb kit.  This should rule out a fuel problem.

If it starts right back up then the ignition is probably fine.

Before doing anything else I would replace the spark plugs.  I recently spent way too much time on a Husky saw and it turned out to be a bad spark plug...$5 would have saved me several hours of time and troubleshooting as I could not find anything else wrong with the saw.

NEW spark plugs first!

Eric