Sounds like no spark. Have you checked that yet? Being out in the rain for a week the magnets on the flywheel could have rusted over causing weak or no spark. First thing would be check the spark with a known good spark plug by grounding the threads of the plug to one of the head bolts and pulling the rope. You will be looking for a nice blue spark. If no spark pull the blower housing and check to see if magnets on the flywheel and coil legs are rusted. If so remove the rust with sandpaper.

 

I leave push mowers in the rain for years without major problems...till they rust out. Then I pick up a new one at a yardsale for $10 and repeat (I only use them for the dog pen).

Sounds like you have no spark as Forshee said. Check the simple things like the plug first. One of the first things to rust and stick on many outside kept mowers is the engine brake. When you release the brake by pulling the thing at the handle (which also allows spark on most) check to make sure the brake handle is actually pulling the cable and moving the little lever on the left side of the engine. Hold the brake down and then see if you can move that lever a bit more by hand. 1/8" too little and she won't start.

I don't find many problems with rusty coil legs on modern engines, but it is a possibility. Some coils are beneath the flywheel which can be a pain to get to...but that type usually don't get wet and go bad.

If it has an on-off switch, unplug it and check again for spark. Those switches just ground the coil to kill spark and can fail, although rarely.

 

So update, I went over to his house on my lunch break and checked the Spark and it was fine. I tried the starting spray and got it to turn over and turn on but it would then would shut off. I checked all over and couldn't find any rust, he said it was left outside for three days. So I told him I'd come back over after work and see what might be the problem.

 

If it has spark the rain is a red herring, UNLESS water got into the fuel. Most mowers won't allow water past the vented cap, so I've never seen this. You can try dumping the gas but I'd be surprised if it works.

Your new symptoms sounds like a very common clogged main jet. Pull the main jet out of the bottom of the carb. It's a 1/2" "bolt" on the bottom of the carb bowl if the engine is a B&S, others use 10mm. Don't lose the gasket on this bolt (it may stick to the bolt or bowl, if so leave it there). Make sure the tiny holes are clear of dirt! This is the #1 problem with these engines and why they get thrown out, but it's a 5 minute fix. Usually can do it with the carb in place but you may have to remove the filter housing.

When you pull this jet out it will also drain the gas tank. Water is heavier than gas so it will flow out first. Water will have droplets, gas won't so it's easy to tell.

That bolt/jet holds the bowl on the carb. The bowl will usually stick in place when it's removed. You can leave it in place, clean the jet and put it back in to test. I always remove the bowl and clean out the crud, but I don't know how handy you are. Sometimes on older engines the rubber bowl gasket swells and is hard to re-install. That's up to you.

 

OIL? With low oil sensor, seems like it may be a culprit.