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I have an MTD rider with a 25 hp Briggs. Mower was running fine. At the end of last season I replaced the main drive belt. First start attempt after belt replacement resulted in a back fire. Second attempt started up fine.
Drove tge mower to verify the belt was good to go. Parked the mower and not will will not start.
I have verified spark, changed plugs, verified fuel is reaching the carb and looked for flywheel sheer issue. All looks good. Will not even fire when starting fluid is sprayed into the air intake while cranking.
.I'm stumped.. the fuel cut off solenoid is working. I have noticed the fuel blown is dry after trying to start.
Open to thoughts and ideas.

Thanks

Fuel pump possibly?

MowerNick said:

Fuel pump possibly?

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Replaced

Put approx. a short table spoon of gas in the top of the carb and if it starts and runs a few seconds there's still a lack of gas problem .
Flywheel key can be checked without pulling the flywheel , but being it ran for awhile my money is on
---- not flywheel wheel key ----

SeniorCitizen said:

Put approx. a short table spoon of gas in the top of the carb and if it starts and runs a few seconds there's still a lack of gas problem .
Flywheel key can be checked without pulling the flywheel , but being it ran for awhile my money is on
---- not flywheel wheel key ----

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Poured fuel in both the top of the carb as well as directly into the cylinder. No start. Flywheel key looks to be as it should be.

IF it does not at least fire with fuel down the plug hole and you confirm there is a spark then :-
1) flywheel key is broken & engine ignition is out of time
2) Valves are not working or our of time
3) con rod is broken and piston is not moving in the bore

bertsmobile1 said:

IF it does not at least fire with fuel down the plug hole and you confirm there is a spark then :-
1) flywheel key is broken & engine ignition is out of time
2) Valves are not working or our of time
3) con rod is broken and piston is not moving in the bore

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Have pulled valve covers and valves are opening and closing. No bent push rods, etc.
Can put fingers over the plug hole and crank the engine. Can feel suction and exhaust pressure.
Will physically pull the flywheel and check the key. Looks fine, but have not actually pulled the flywheel off
Thanks for the thoughts. Will take a closer look at the flywheel key with the flywheel off.

crobbins175 said:

Have pulled valve covers and valves are opening and closing. No bent push rods, etc.
Can put fingers over the plug hole and crank the engine. Can feel suction and exhaust pressure.
Will physically pull the flywheel and check the key. Looks fine, but have not actually pulled the flywheel off
Thanks for the thoughts. Will take a closer look at the flywheel key with the flywheel off.

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the think about checking the flywheel key is you have to remove the bolt to at least look at. If the nut/bolt isn't then properly torqued the key will shear on the first start attempt even if the flywheel was never removed.

ILENGINE said:

the think about checking the flywheel key is you have to remove the bolt to at least look at. If the nut/bolt isn't then properly torqued the key will shear on the first start attempt even if the flywheel was never removed.

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Thanks for that information. I don't think it's out of time, but it's the only thing that really makes sense.

how did you verify spark, light or gap tester. light style can fool you.

After you pull the flywheel and the key is good you need to verify you have spark. Get a $5 spark tester.

If those two don't work, see if you can find a $15 carb on Amazon. New carbs will often solve problems.

Do all of what everyone has suggested above. If you do and everything checks out but you still have no start, check for spark by either using a spark checker plugged in between the plug wire and spark plug or by grounding the removed and cleaned spark plug to the engine block (with the plug wire still attached) and cracking the engine over. If you have no spark; your ignition coil will need to be replaced. You’ll need to order the correct coil from your favorite parts source. Remove the fan shroud, remove the small two small bolts that attach the coil to the engine block, unplug the spark plug wire from the plug and the small “kill wire” from the coil, and the coil will come free. Reverse procedure to install the new coil, but leave the 2 bolts slightly loose, slide a business card between the coil and the edge of the flywheel then turn the flywheel slowly (insuring the card stays between the coil and flywheel and doesn’t slide out) until the magnet on the flywheel is fully pulling the coil to it. Tighten down the two bolts, remove the card, and complete the rest of the reverse procedure.

if the $5 doesn't work, get a good one! or use a new spark plug grounded to engine & crank over. or throw parts at it - NOT,

Caoeal Spark Plug Tester, Adjustable Ignition System Coil Tester Autos Coil on Plug Spark Circuit Tester, Repairing Diagnostic Test Tool https://a.co/d/0WohZKj

Woops. Amazon Cost is up to $7.49. All gap testers work the same. Set it to lawn mower or LM which is usually 10cm and see if it arcs.

If it was running good with the old v belt and that is all you done was replace the v belt and you had a failure put the old v-belt back on and test.
(just kidding)

Had this same thing happen to a guy that called me on phone and said he had just changed the oil in his vec and afterwards if would not even crank. I told him to put his old oil and filter back on the engine and test. He was not mechanically said yes, I still have my old oil and filter. I said re-ininstall both. He thanked me and said ok. I'll let you know.
I said don't do anything I'll come check. I'm a mechanic, electronic tech and electrician) His starter solenoid had failed.
We did not have to re-install his old filter and oil.

STEVES said:

how did you verify spark, light or gap tester. light style can fool you.

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Both light and grounding electrode to frame