Likely either the engine is flooded or low compression.
A simple go no go compression test is remove spark plug and press a thumb or finger firmly over the plug hole and crank engine. It should forcibly push your finger and make a loud PFFfft sound. No or little sound equals insufficient compression.
If the push rod was not bent, there was no reason to replace. If it was bent then I question how you set proper valve lash with new pushrod as the typical cause for a bent rod is a displaced valve guide.
If compression is OK then likely it's simply flooding and you have a carb float/inlet needle issue. Crank engine, remove plug and if it's saturated with fuel then it's flooded and a flooded engine will not fire, even with starter fluid.
Replace the fuel lines. I had the same problem with one of my riders. The inside of the fuel lines had rotted and they were collapsing when they tried to suck the gas through them.
New lines and it ran all day!
Question edited for clarity and make sentences.Question moved form Cars and Trucks to make model category.My guess is you have a leaking valve. The compressed air in the leak down test is closing it. Remove the heads and lap the valves. Check the valve stems are true and not sticking. The variation is compression 50 v 30 is too great.https://www.google.com/search?q=Briggs+%26+Stratton+23+HP+VANGUARD.+right+side+runs+cold..
Question edited for clarity and spelling.
Question moved from Motorcycles category.
Please proof read before pressing 'Post Question'. Your 'Bolson' doesn't exist!
https://www.google.com/search?q=Bolsen+1.5HP+158cc+briggs+%26+stratton
Surging is usually caused by an air leak in the inlet manifold.
Remove and sharpen the blade. If the blade is sharp, it will slice though the grass with no resistance. Over time, the cutting edge gets blunted by stones, grass and soil. If that doesn't fix it, remove the carburetor, strip and clean all the jets. Make sure you count the turns and write down any pilot jet settings.
