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Long time listener, first time caller - watched every video I could find on YT and read through every post here and on Reddit and am looking for some help!

Craftsman T1200
Model: 247.203726
DOM: 02/2018

Purchased used from a gentleman that fixes small engines, said it was in perfect condition and running as it should. Looks almost brand new. I mowed my lawn three times with it, on the forth time I made it about 100ft and it stumbled and died. It will crank but won’t run. Below are the things I have done / checked-

Brand new carb (also took it out, completely disassembled, cleaned and rebuilt)
Fuel Solenoid is functional and clicks when the key is turned (also disassembled and cleaned)
New air filter with pre-filter
Fresh gas (93 oct)
New NGK spark plug
Added fuel cutoff valve and new fuel filter
Battery is less than a year old and fully charged
20A fuse is good to go
Compression is at 150
Oil is at the correct level and was replaced in July

No matter what I do it just won’t run or fully turn over, just spins and spins and spins. Any help or ideas on next steps would be beyond appreciated, a few weeks behind on my cut and a service tech can’t make it out for two weeks, would honestly love to fix it myself but didn’t want to dig into the engine if I don’t have to.

As soon as it dies and won't start remove the air filter and put a teaspoon of gasoline in the top of the carburetor and try it .

What engine is on the riding mower? We need the model number off the engine shroud. You have fuel, and compression which leaves air, spark, and timing. I would lean towards timing, so check the flywheel key and the valves. I bet the flywheel key is sheared. Maybe the valves came loose? I would also check for Spark because even though you replaced the sparkplug, the coil could be bad. I think this tractor has the chinese engine that can sometimes be finnicky.

First off thanks for the quick replies - will get the engine model number in a bit here!

I did forget to mention I tested for spark and can confirm it’s getting it via plug tester
I tried gas in the air intake as well as starter fluid with no luck
I also removed the plug and spun it a few times to clear everything out in case it was flooded

My initial thought after all this was the flywheel key (timing) and excuse my ignorance here but I have no clue where it is or how to check it, from my understanding i need to remove the plastic grate on top and get a puller to remove the flywheel to access the key?

I also found this number on the tag along with the model number I listed above - 13A278XS099

Good reference here I found - and I believe this is the part - https://www.searspartsdirect.com/product/5b5p5lzaws-0071-247/id-951-10307

Looks like this mower uses the 4P90HU MTD engine. Looks like compression is supposed to be 55-80 so I am wondering especially with the high compression reading if then valves are opening and closing properly. May need to remove the valve cover and inspect the push rods and make sure everything is opening and closing as it should.

So I can confirm it is the flywheel key, took it apart today and it’s not even in there. Where can I get one of those? Are they universal? Lowe’s? I can order them but given Asheville just got destroyed by Helene I doubt anything will arrive in a timely manner. Just wanted to ask if it’s a common part a hardware store would have, thanks!

Part Number: 951-10307

Any good hardware store with those orange cabinets of stuff may have the woodruff key you need. The fun part is choosing the right one.

Matnetik said:

So I can confirm it is the flywheel key, took it apart today and it’s not even in there. Where can I get one of those? Are they universal? Lowe’s? I can order them but given Asheville just got destroyed by Helene I doubt anything will arrive in a timely manner. Just wanted to ask if it’s a common part a hardware store would have, thanks!

Part Number: 951-10307

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Order extra flywheel keys and get the proper OEM torque value for the flywheel bolt. Most are a tapered shaft. Polish the crank end meaning remove no material, just polish and clean up. The inside of the flywheel needs cleaned up/polished too.

Some flywheels have a key that is kinda hidden until you remove the flywheel. Key is in a slot slightly down on the crank end. Once you get the flywheel off it will confirm it for you.

Nice catch on finding the missing key.

slomo said:

Order extra flywheel keys and get the proper OEM torque value for the flywheel bolt. Most are a tapered shaft. Polish the crank end meaning remove no material, just polish and clean up. The inside of the flywheel needs cleaned up/polished too.

Some flywheels have a key that is kinda hidden until you remove the flywheel. Key is in a slot slightly down on the crank end. Once you get the flywheel off it will confirm it for you.

Nice catch on finding the missing key.

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Appreciate this! Ordered 5 last night just to have - will get things cleaned up before they arrive so it’s ready to go and report back - need to go to a few hardware stores today to fix things around the house so I’ll take a peek while I’m out for one!

Well got the flywheel off and no luck - the key is perfect. I thought it was the key from looking at the top. No idea where to go next with this one other than taking the valve cover off and inspecting, just seems odd that it would be an engine issue.

Battery is at 12.26v and is new, even connected it to my car with cables and no luck, seems like it doesn’t always want to spin.

https://www.dropbox.com/scl/fi/r5uy...sues.mov?rlkey=mfxq3i36fzzzeut384egkrw58&dl=1

Matnetik said:

Compression is at 150

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That is high. Might need to de-carbon the cylinder and valves per your engine manual. Briggs motors are mostly 8:1 compression. Definitely inspect the valve lash or lack of.

Matnetik said:

Battery is at 12.26v and is new,

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Tells me your battery might not be charging and or definitely needs charged. At rest 12.6 is fully charged. Take battery to any auto parts store. They will check for free. Might have a weak cell pulling the others down.

slomo said:

That is high. Might need to de-carbon the cylinder and valves per your engine manual. Briggs motors are mostly 8:1 compression. Definitely inspect the valve lash or lack of.

Tells me your battery might not be charging and or definitely needs charged. At rest 12.6 is fully charged. Take battery to any auto parts store. They will check for free. Might have a weak cell pulling the others down.

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Yeah battery was just low from trying to crank it, I charged it and it’s good to go now - just won’t turn over or run - I suppose the next step is opening the valve cover and inspecting

Matnetik said:

Yeah battery was just low from trying to crank it, I charged it and it’s good to go now - just won’t turn over or run - I suppose the next step is opening the valve cover and inspecting

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Take the battery and have it LOAD TESTED. Charging a battery doesn't tell the whole picture. Once you hit the key, a dead cell will make the entire battery fall on it's face delivering less than required current.

Once you confirm you have a good battery, then attack carbs and other mower parts.

Matnetik said:

Brand new carb (also took it out, completely disassembled, cleaned and rebuilt)

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OEM carb or Chinese amazon ebay specials?

Matnetik said:

Fuel Solenoid is functional and clicks when the key is turned (also disassembled and cleaned)

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While you had it out, did you watch the plunger move when you hit the key on and off?

Matnetik said:

New NGK spark plug

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Do you have spark from the coil? So now 2 plugs and no fire? Just read you claim to have spark.

Matnetik said:

Added fuel cutoff valve and new fuel filter

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Good man now use them.

Matnetik said:

Battery is less than a year old and fully charged

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Already covered this. Needs tested and confirmed good.

Matnetik said:

20A fuse is good to go

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How was it checked? Visually or a meter? Sometimes they can look good and be blown.

OEM carb, checked spark with the spark plug tester. Checked fuse with the fuse tester. Will take the battery to have it load tested but it’s only about a year old, could still be an issue!

I just popped off the valve cover and one of the rockers was loose and I could spin it around. Here are a few pictures, I wonder how much deeper I need to dig into this

Matnetik said:

I did forget to mention I tested for spark and can confirm it’s getting it via plug tester
I tried gas in the air intake as well as starter fluid with no luck

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So you have spark and she won't fire off with starting fluid? A-maz-in. Flywheel key is good. 150psi means you need to pull the valve cover. Beat me to it LOL. Nice pic. Yeah you have issues. Now investigate WHY the rocker came off. Never ran valve lash? Bent push rods?

Does your engine have a valve stem cap? If so find it and put it back on. Then set the lash.

Matnetik said:

Will take the battery to have it load tested but it’s only about a year old, could still be an issue!

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Fix the valve issue. If you still have issues have the battery tested.

slomo said:

Does your engine have a valve stem cap? If so find it and put it back on. Then set the lash.

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And we have success! Cranked right over after fixing the rocker, running a bit sloppy but I’m sure it’s from all the fuel in the cylinder, tomorrow I’ll run some seafoam through it and let it run for a while and see where we’re at- thanks for all the help and will report back, learned a ton about the mower from this process

This appear to be the valve stem cap just laying there.

Yep it sure was the stem cap sitting there - tightened the rocker stud to 200 in lb per manual, set TDC and valve lash on the intake and exhaust, reassembled and it’s purring like a kitten! Running better than before, thanks for everyone’s input, glad I was able to knock this out without spending any money on parts or labor!

Matnetik said:

Yep it sure was the stem cap sitting there - tightened the rocker stud to 200 in lb per manual, set TDC and valve lash on the intake and exhaust, reassembled and it’s purring like a kitten! Running better than before, thanks for everyone’s input, glad I was able to knock this out without spending any money on parts or labor!

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Thanks for sticking with us and glad to hear she is running again.

Recommend downloading your engine manual. Read it cover to cover. Things like valve lash, CLEAN THE COOLING FINS and such are yearly tasks we all need to do.

slomo said:

Thanks for sticking with us and glad to hear she is running again.

Recommend downloading your engine manual. Read it cover to cover. Things like valve lash, CLEAN THE COOLING FINS and such are yearly tasks we all need to do.

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Absolutely, downloaded the PDF so I am set to go. Cut about an acre yesterday and it ran strong The whole time. Hopefully this thread will help someone else who may have a similar issue, and fortunately Sears shipped me 9 flywheel keys (I only ordered 5) so I have plenty if I ever have a problem.

Cheers all and take care!