Pony 42X Model 13A877BS066 Engine 4x90HUA Surging

[Bridanielson]

I'm at the extent of my knowledge. Reaching out for help!

Bought this new about 2 years ago, never had a problem until a couple weeks ago. Cutting grass as normal made a turn and it just died. Started right back up, but surging. Let it sit over night and it ran just fine until it got hot. Then died, starts and surging.

I started going through the steps to pinpoint the problem.
Changed fuel
Changed spark plug
Changed fuel filter
Changed air filter

Continued to repeat the issue when it got hot.

Cleaned the carburetor, and it actually got worse, surging is 100% of the time now.
Changed fuel again, added cleaner additive
Ordered and replaced the carburetor assembly, no change constant surging.
Confirmed the fuel lines not clogged
Replaced the ignition coil
Replaced the throttle bracket and both governor springs
Checked and adjusted the valve lash
Pulley teeth are OK

Always starts, can't maintain RPM.
I don't know what to check next to be honest.

 

[bertsmobile1]

99% of the time surging with a governed engine is because the air: fuel ratio is too lean to maintain a constant speed
So either not enough fuel is getting in or air is entering the engine after the fuel is added by the carburettor .
Floating debris builds up in the fuel tank and gets pulled into the fuel outlet by the fuel flowing then floats away the instant the engine is stopped .
Some think cleaning a carb is just squirting some carb cleaned down the throat ( does nothing ) or removing the float bowl and tipping the accumulated crud out.
Proper cleanin requires a full strip down, ultrasonic cleaning, dip cleaning , boiling the reassembly with new service parts .

 

[Bridanielson]

I replaced the carb assembly with a brand new one. So assuming its not defective giving me the same symptoms. So I suspect air...

Ordered a leak down tester, will try that over the weekend.

 

[Rivets]

Sounds to me like you have either a fuel vaporizing problem or a fuel line collapsing problem. To to prove me wrong this may sound very stupid, but this is what I would try the next time it starts surging and dies. Get a long piece of fuel line so you can connect it directly between the fuel tank and the carb, away from the heat of the engine. If the engine now runs properly you will have to figure out which problem you have.

 

[bertsmobile1]

Unless you bought it from a genuine specialist mower parts supply company ( ant that rules out Evilpay, Ammozone & Feaces Book ) then here is zero reason o expect the brand new carb is a good one and not a faulty one bought as scrap metal then sold online to cheapskates who do not know any better .
Sorry if that sounds cruel but it is a fact of life now days
A leak down tester will not help with your surging.
If yopu don't know how to test for something ask & we will be happy to inform you, usually of several different ways to do the same thing .
So to test for an air leak you start the engine without the blower housing on then saturate the engine from the throttle butterfly pivot to the head with WD 40 or similar from a trigger pack, not a spray can .
While doing this work the throttle up & down with your finger on the governor arm
Clouds of white smoke in the exhaust signifies an air leak.
Manifold suction is greatest just as the throttle plate backs off

 

[Bridanielson]

I bought an MTD carb. If there is a better brand let me know and I'll get another one.

Saturating with wd40, some white smoke, lots of loud back fires.