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I have an issue that may have been covered in another thread, but I am hoping you all can either point me there or just help out here.

This engine is in a Scotts/John Deere lawn mower. After running for about 45 minutes it starts to run rough and the RPMs start to ebb and flow. Eventually it starts shaking and dies. Initially, it would run if I kept the choke on and I could at least get it back to the garage. That no longer works. However, if I let it sit for an hour or so it starts up fine and runs smoothly.

I thought it must be a carburetor because this is a used tractor. I took that off and it was in good shape. I cleaned what little grime there was and put it back on. It ran fine for one mowing and now its back to where it was.

I am new to this kind of repair. What should be my next attempt to fix this? I dont think the gas is bad. It was empty when I got it and have been using gas from the same can. It mowed the lawn just fine 5 times. The fuel filter looks good.

Any help would be much appreciated! Educate me!

Thanks in advance!

Welcome.
Your symptoms point to floating debris in the fuel tank getting sucked into the fuel tank outlet and partially blocking off the fuel supply
When it runs bad, pull off the fuel line and blow back through it
If you can run for another 1/2 hour or so before the problem comes back that sort of confirms this

The other problem with JD fuel tanks is some of them feed from the top via a pipe that goes down near the bottom.
These ones can get a split in the outlet pipe so they only work till the fuel gets to the height of the hole
You diagnose this by topping the tank up the instant the problem happens
If it always happens when the fuel is at the same height in the tank then suspect a holed outlet .

bertsmobile1 said:

Welcome.
Your symptoms point to floating debris in the fuel tank getting sucked into the fuel tank outlet and partially blocking off the fuel supply
When it runs bad, pull off the fuel line and blow back through it
If you can run for another 1/2 hour or so before the problem comes back that sort of confirms this

The other problem with JD fuel tanks is some of them feed from the top via a pipe that goes down near the bottom.
These ones can get a split in the outlet pipe so they only work till the fuel gets to the height of the hole
You diagnose this by topping the tank up the instant the problem happens
If it always happens when the fuel is at the same height in the tank then suspect a holed outlet .

Click to expand...

You know what I think you hit the nail on the head! I looked in the tank and it looks like there is some kind of rubber seal that crumbled and is in the bottom of the tank. Never crossed my mind! I will see what I can do to clean it up and hopefully that solves it!

Check the underside of your fuel cap
The older mowers use vented fuel caps that have large rubber seal in them.
Your mower is getting to the right sort of age to have the rubber seal fall apart.
Without the full seal in the cap some do not vent properly and that can cause a vacuum lock as well .