Craftsman riding mower, 17.5 Briggs and Stratton motor. New carburetor, getting fuel to cylinder, have spark when plug & wire are laying on frame, tried many times to start and one time it did seem to fire but did not start. Have not found a problem with Safe wiring or connections. Does the coil ever go weak ....or is it either good or bad.

Thanks!

Will it fire on starting fluid? Mine had a safety switch in the seat that went bad.

Check the compression.

Yep.

You need 3 things - air, fuel, and fire. There may be a carb problem if you are getting air and fire. I recently had a carb on a Briggs and Stratton that would allow the engine to run for a few seconds. The carb would pass enough fuel to allow that short run, but not to fully run.

Will check compression and doublecheck the safety features. Starting fluid may be first.

I am not a small engine expert but will share my experience.
My understanding coils or like light bulbs, good or no good but not weak. However if the coil gets out of adjustment in the space from flywheel the spark can weak. color of spark indicates temperature of spark. Red, white or blue. Red being coolest and blue hottest. White or blue should fire a good spark plug. Have you tried a new plug?

Two issues I have had with my 17.5 Briggs.
The shut off solenoid in the bottom of the fuel bowl would not open. I don't remember if it was stuck or not getting 12 volts to open. I can't remember.
Other thing was the fuel filter became clogged. I had fuel when I disconnected from carb and placed gas line on ground, but would not flow into carb through normal conditions. Mine is gravity fed so carb is just slightly below gas tank. I assume there wasn't enough elevation when installed to carb. New fuel filter solved.

As asked, will it start on starter fluid, WD40, or brake cleaner?

When was the last time it ran? When it ran the last time did it give any indication of current trouble? How old is the fuel? How strong is the spark? What happened to the old carburetor did you toss it out because it got gummed up? It may be worth disassembling that cleaning it and reinstalling it. Your answers will be telling and helpful

If it’s getting spark to the plug it’s not a safety switch.
Drain and fill fuel tank to half full and put in new plug and try.

Watch starting fluid through the air cleaner and carb... That stuff can melt plastic parts. I'd put a shot in the cylinder.

First thing I do after checking to make sure it has gas is to pull the spark plug and clean it with a wire brush and then reinstall. At least 90% of the time my issues are just a fouled up spark plug that needs cleaning. The longer that gas sits in a tank the nastier it gets and does not burn clean. The spark plug takes the brunt of that "does not burn clean" part.

Yep! What you said reminded me of my recent starting problem with a Honda 2200 watt generator. Dang thing would not start. I pulled the plug, wire brushed it, screwed it back in and fired up the Honda on the first pull.

I don’t think I ever fixed a small engine by cleaning or replacing a spark plug. If you are getting fire I don’t think it’s the plug safety witches or coil. I’d bet it’s fuel. Is the plug wet after cranking?

Might be flooded. This uuuuh, guy I know has flooded a few. That’s when brushing and drying the plug helps.

Yes the plug was wet.

Bad gas...???

Gas is at most two months old and non-ethanol.
It ran fine until a few weeks ago when it flat died.
Have not been able to restart.

Stored inside or out?

Drain fuel into clear jar and let sit and see if water settles out

Gas cap clogged , i had that problem once

Replies on these topics are pretty comical. Three things to run? No, it's four! Air, fuel, spark, and COMPRESSION.

It's out of time or has a bent valve, broken spring, or piston/ring issue I bet. Other than that, what's the color of the spark when tested against the head? I am guessing two cylinders. Any difference in the plugs left to right? If the plugs are coming out wet and you have spark with a solid blue color, it's low on compression or has a MAJOR carb problem.

Had a class in school we were taught 3, fuel compression and fire. Air was part of fuel.

Well…right or wrong, I always assume we have compression. At least till nothing else works to solve the problem.

It could be, like someone mentioned, bad fuel. One of my weed eaters is real picky on fuel. Every once in a while I have to drain the fuel and replace with fresh. That solves the problem.

There is one thing about the OP’s problem that I wonder about. Did the engine used to run (I think the answer is yes)? Has the engine ever run with the new carb? If it has never run with the new carb, then there’s the problem. Or, it could be that the carb gasket is installed wrong. This guy I know (me) flipped the carb gasket when installing a new carb. It sputtered but would not run. Took the carb back off and realized what I had done. Put it on right and it ran great.

So, remove the carb and check the gasket. And while it’s off, make sure all jets are clear. And think about a new new carb.

I have an older 42 inch with a 17.5 Briggs Polan by AYP, 20 years old. It is single cyinder. No comparison to newer ones, I assme.

I have read or heard about newer Briggs flattening cams. That could cause these symtoms. I would think you would notice a difference in sound engine make when cranking on starter. Any idea how a homeowner could check?

Take the cover off the valves and look to see if they are moving. Turn flywheel by hand and see if resistance changes. Compression tester, can borrow from local parts store.