Help with Craftsman YTS3000 tractor

[JMoney]

Hi all I've been working on a lawn tractor that sat 3-5 years and reaching my wits end. It's a Briggs OHV 21HP 540cc platinum XRD model 3318767.

The motor is surging (will run sometimes at half choke, but will surge then die at run and will die at full choke and idle) and burning oil at startup. There's oil under the valve cover and compression is 110PSI cold. Valves are Intake .004 and exhaust .006 about a half inch piston travel past TDC with both valves closed. Just replaced the carb. I'm guessing this is a ring problem but I would expect lower compression. I did initially make the mistake last season of adjusting the valves without measuring piston position, if that could have damaged the rings.

It's a Briggs OHV 21HP 540cc platinum XRD model 3318767. Initially replaced fluids and cleaned out carb and it ran fairly well for a few hours last season after having the valves adjusted. It would still burn a lot of oil after being transported but then would clear up. It was put away without having the tank/float drained and found with a case and cylinder full of fuel this month. Oil was replaced.

Should I replace the rings? Is it much of a job to open one of these up? I've had flathead brigs push motors apart and saws but nothing with OHV.

Edit: here is a video of it running https://photos.app.goo.gl/ov42hbUgxQ19d2hf6

 

[Larry B]

Rings are probably fine. Common problem on the engine is blown head gasket between cylinder and pushrod gallery. Still prob has carb issue too.

 

[JMoney]

Well that is a relief. I think I can handle a head gasket. What could be going on with the carb then? It's brand new and the symptoms are exactly the same before and after. I added a fuel filter maybe it isn't flowing enough but it only has a few hours on it.

 

[Larry B]

If it is a gravity fuel system you may need to use a screen type filter vs a paper type filter. Surging issue that gets better with some choke usually means an air leak or restricted idle circuit. The plastic intake manifold seals to the cylinder head with a rubber o ring type seal. Run the engine at idle and spray some carb cleaner where the manifold meets the head. If engine changes how it runs you either have a bad seal or cracked manifold. Common problem is manifold cracked and o ring hard as a rock and not sealing.
If you pull the head steel push rod is exhaust and aluminum is intake. Don't lose the caps on the valve stems. Torque head bolts to 225 in lbs.

I have a mower in the shop right now with that engine doing a head gasket job on it