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Hello,

I have a problem with my Partner P145107HRB tractor (it's an EU Husqvarna brand) with Briggs&Stratton engine, model no. 31a507-0743-b1, hydrostatic transmission.
For the past few days I'm unable to mow the grass with a deck lowered below 6 (height adjustment is between 1-6, I usually mow using 4). Even though I'm able to run the tractor on 6, after 15-20 minutes, the issues occur. Here is an example of it:


Sometimes the engine dies or shoots through exhaust (really loud bang).

What I've done so far:

- changed and adjusted the Nikki carb
- changed the fuel filter
- cleaned fuel tank
- bought fresh petrol
- adjusted magnetron using gap gauge
- checked the sensor underneath the seat - it works for sure, after unscrewing it and holding it with a finger the problems still occur, but if I remove my finger it kills the engine instantly.
- checked grass catcher sensor, although as you can see the problem also occurs when I'm not moving
- cleaned the deck with pressure washer

During the ride nothing happens, I can ride with a highest speed. I tried moving the blades manually, and they seem to rotate fine. Adjusting the carb with blades on and problems occurring seems making no difference.

Sounds like it is running rich under load. Could be a problem with the high speed jet in the carb. The nikki carb contains a small jet in the bottom of the emulsion tube that will fall out when not looking when cleaning. You said that you changed and adjusted I'm not sure that means you replaced it. I would also change the air filter if not done already, and make sure there isn't gas in the oil which can cause a similar run issue when pulling gas fumes from the breather.

This series of Briggs engines are bad about blowing head gaskets. With the valve cover do a leak down test to check for blown head gasket. These gasket blow between the cylinder and push galley so if the exscape air is louder at the push rod galley than at the oil fill tube it a blown gasket.

May not be the problem but is something I have learn to check for everytime I do a valve adjustment on these engines. Besides it doesn't hurt to check valve adjustments while the cover is off too as they tend to open up over time.

I replaced the complete carb for a new one, so there should be no issues with it now. I will check the oil tomorrow. I was also thinking about valve adjustment, will do it tomorrow.

To me it sounds like 8 stroking ( google it ) which is caused by running too rich
It could also be an exhaust valve with way too much valve lash which is chokeing the engine when the throttle is wide open
You can manually move the throttle by pushing the governor arm.
At idle it is barely open when you engage the blades & load up the engine it opens wide, which you can do manually to diagnose the engine.