Briggs 18.5 hp Wont Run

[biggertv]

While you're in there check the Flywheel Key. Rare on a Rider but I've seen it especially if Nut is not torqued properly. Even if not sheared, a worn Key Way will give you spark but wet plugs.

 

[kkjfjns2014]

While you're in there check the Flywheel Key. Rare on a Rider but I've seen it especially if Nut is not torqued properly. Even if not sheared, a worn Key Way will give you spark but wet plugs.

How would I check that? Taking the top flywheel off?

 

[TobyU]

Wow, I noticed a yellow spark when I was testing the plug and didn't even know that was a thing. That is awesome. I'll be ordering a new coil today

As someone else said earlier, do a thorough and proper diagnosis before you throw more parts at the machine.
This happens way too often with homeowners and by the second or third attempt they stumble into it and get it right and it just creates positive reinforcement of doing a bad pattern in the future.
I understand it's frustrating you have to do something but we need to back up before you waste money on a coil and like someone else said make sure you order one off eBay or Amazon so it will be $16 shipped to your door instead of paying 60 at a lawnmower shop or for a Briggs & Stratton brand.
Two of the carbs flooded out one wouldn't run it all but the question now is if you take the plug out and put a fresh dry plug in there can you get it to run on carb cleaner spraying it in the intake of the carb????
If you can then it certainly isn't the coil at least not unless it runs for a while and gets hot and then they coil breaks down and then it dies and then starts the process all over again once it cools off but that's a secondary diagnosis. You are well before that now.
Also, make sure the spark plug is gapped no greater than .030.
That is the spec but I like to get them about .027 to .028. in fact, it makes little difference as you could gap it at .020 or .025 and you wouldn't notice a bit of difference in the performance or the power but as it gets older and more carbon on it and the coil gets weaker or if the coil is getting borderline and ready to fail in the next couple of years anyways, it will last longer and you'll get a more consistent stronger spark with a smaller gap.
So tighteris better than looser on the spark plug gap -- within reason!

So get back to the basics. If the cylinder isn't flooded out and the plugs not wet now you just want to make sure the plug Sparks when you spend the engine over by looking at the spark jumping at the tip and it should be a bluish to whitish color. Red will still fire and run but it is weaker and yellow you really hardly ever see I guess unless it's bright and sunny out and it's hard to see anything.
If the cylinder is dry and the plug is not fouled out and you spin the engine over at normal speed and provide a fuel source into the intake, if the engine is mechanically sound which means the valves working properly and having compression and having spark...it will run for a few seconds until the fuel source you provide runs out.
In fact, you could take the carburetor off and lay it on the ground and squirt the carb cleaner in the side of the engine where the hole is and it would do the same thing but that's not a good idea because they will be no method to govern it and you could overrev and blow it up or grenade your internal governor/slinger because with no carb on the engine to block off the air flow the only way you have to stall it out until it runs out of fuel is to put a thick rag over the hole and kill its intake of air which is a little hard to do.
My point is that the carb has nothing to do with the engine actually running or not.... Providing fuel and at the proper amount and ratio is what determines whether it a mechanically sound engine will run or not. That just happens to be what the carburetor is supposed to do.
So go get that can of car cleaner or a little spray bottle and pour some gas in it and check your spark plug and see if this thing will run for three or four seconds at a time on an external fuel source.

 

[smhardesty]

Well stated, TobyU. He most definitely needs to diagnose, step by step, instead of taking guesses and throwing more money at it. Yeah, eventually he might actually hit a combination of new and old parts that result in the engine starting and running, but the real problem might not ever be determined. If you throw enough new parts at ANY engine, it will eventually run, but by that time you might have a complete new engine sitting in front of you. Building an engine by buying new parts will make for an awfully expensive engine.

 

[biggertv]

How would I check that? Taking the top flywheel off?

At least remove the nut and washer so you can see the key way. It's probably ok unless it's been removed before and not torqued properly.

 

[Forest#2]

Lots of good info previously:

Just a hint that has been mentioned.
Turn off the gas to the carb.
Start testing with a dry clean spark plug and also crank the engine over se3veral times with the plug out to purge out any flood gas that might be in the cylinder.
Set the throttle at just about midway.
Squirt spoonful of gas into the carb throat while it's cranking fast.
If it briefly tries to run the engine needs gas from the carb to run.

If it don't attempt to briefly run, it has ignition or compression issues.
Does the engine have any compression? (at least 80psi)

You may have started out with two issues with the engine, a bad carb and something else and sometimes two issues are harder to sort out.

Let us know how this test goes???