brand new B&S surging after 1.5 hrs use

[animattor]

I bought a new mower with a B&S 750EX engine. Used it about 1.5 hrs on low throttle (thought I would save gas). Then the engine started surging. I looked at the spark plug and it was covered in soot. I changed the spark plug and it is still surging. Does this sound like a mechanical issue (warranty service) or did I just gum up the carb running on low throttle? The grass was wet and the deck was pretty clogged when I checked it after it was surging. It still starts on first or second pull but constantly surges.
-new, full oil
-fresh gas
-clean air filter

Thoughts? Thanks!

 

[Rivets]

Run the unit at full throttle. You’ve probably gummed up or carbon up the unit. Should clear up you problems.

 

[animattor]

Run the unit at full throttle. You’ve probably gummed up or carbon up the unit. Should clear up you problems.

well I ran a full tank of gas at full throttle and the surging didn’t stop. I’ll have to bite the bullet and take it to the shop or try my hand at cleaning the carburetor. I’m guessing I won’t be able to get warranty service due to “misuse” since I ran it on low throttle.

 

[olds394]

I have the same issue.
If I hold the governor spring the surging stops, baffles me.

 

[SeniorCitizen]

well I ran a full tank of gas at full throttle and the surging didn’t stop. I’ll have to bite the bullet and take it to the shop or try my hand at cleaning the carburetor. I’m guessing I won’t be able to get warranty service due to “misuse” since I ran it on low throttle.

How would warranty know you ran it at less that full throttle .

If the sale wasn't registered you may not get warranty work done .

 

[slomo]

Take it back under warranty.

 

[bertsmobile1]

I have the same issue.
If I hold the governor spring the surging stops, baffles me.

urging only happens with a governed engine.
It it was not governed it would just cough then stop
So if you hold the governor open the engine is running on both the idle jet & the main jet
Now when the main jet comes into play it supplies 40% + of the fuel to 95% just before the engine blows up.
You have an obstruction in the idle circuit .
On mower engines the idle circuit powers the engine in a no load situation to around 3500 rpm
This is why the base speed is called "high idle" because it is running 95% on the idle jet
So your symptoms are perfectly normal and is what techs like me do to determine if a carb has a main jet obstruction or an idle jet obstruction.

 

[animattor]

I took it to service today. It took several pulls before the mechanic could start it, and it put out copious amounts of dark smoke when it ran. He shut it off and didn’t ask any questions. I’ll let you know what he says when I get it back.

 

[slomo]

Going with stuck open carb needle.

Should of pulled the oil dipstick and smelled for fuel.

Heavy black smoke is excessive unburned gasoline.

 

[animattor]

Going with stuck open carb needle.

Should of pulled the oil dipstick and smelled for fuel.

Heavy black smoke is excessive unburned gasoline.

if the needle were stuck open does that cause fuel to run out faster? The second tank seemed to go pretty quickly.