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brand new B&S surging after 1.5 hrs use

#1

animattor

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!

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#2

R

Rivets

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


#3

animattor

animattor

Rivets said:
Run the unit at full throttle. You’ve probably gummed up or carbon up the unit. Should clear up you problems.
Click to expand...
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.


#4

olds394

olds394

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


#5

S

SeniorCitizen

animattor said:
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.
Click to expand...
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 .


#6

S

slomo

Take it back under warranty.


#7

B

bertsmobile1

olds394 said:
I have the same issue.
If I hold the governor spring the surging stops, baffles me.
Click to expand...
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.


#8

animattor

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.


#9

S

slomo

Going with stuck open carb needle.

Should of pulled the oil dipstick and smelled for fuel.

Heavy black smoke is excessive unburned gasoline.


#10

animattor

animattor

slomo said:
Going with stuck open carb needle.

Should of pulled the oil dipstick and smelled for fuel.

Heavy black smoke is excessive unburned gasoline.
Click to expand...
if the needle were stuck open does that cause fuel to run out faster? The second tank seemed to go pretty quickly.


#11

S

slomo

animattor said:
if the needle were stuck open does that cause fuel to run out faster? The second tank seemed to go pretty quickly.
Click to expand...
I would say yes.


#12

animattor

animattor

Well I got it back from service. Mechanic told me it was the carb, generically. Mowed the lawn one time, and it ran better but not great. Then I changed the oil after the first 5 hrs usage. And then it wouldn't start at all. It's back at service again. :(


#13

Tiger Small Engine

Tiger Small Engine

animattor said:
Well I got it back from service. Mechanic told me it was the carb, generically. Mowed the lawn one time, and it ran better but not great. Then I changed the oil after the first 5 hrs usage. And then it wouldn't start at all. It's back at service again. :(
Click to expand...
Please follow up once you get answer to issue.


#14

animattor

animattor

the saga continues. I pulled out mower for the first time this season, and it started right up. cut well, ran smooth for about an hour and then started surging again. Fuel bowl is clean, the float moves freely, and i tried cleaning idle jet with canned air (i don't have anything small enough to try physically unplugging the jet). there is no debris in air intake. I put in 75% fresh fuel (mixed with a little left over from last season).

At the end of last season mower was at service and running well.
Here's a video of the surging at idle.
any suggestions appreciated. I'd like to get to the bottom of this. It is still under warranty, but for service, not return. In about 10-12 hours of use it was at service three times last season.


#15

Tiger Small Engine

Tiger Small Engine

animattor said:
the saga continues. I pulled out mower for the first time this season, and it started right up. cut well, ran smooth for about an hour and then started surging again. Fuel bowl is clean, the float moves freely, and i tried cleaning idle jet with canned air (i don't have anything small enough to try physically unplugging the jet). there is no debris in air intake. I put in 75% fresh fuel (mixed with a little left over from last season).

At the end of last season mower was at service and running well.
Here's a video of the surging at idle.
any suggestions appreciated. I'd like to get to the bottom of this. It is still under warranty, but for service, not return. In about 10-12 hours of use it was at service three times last season.
Click to expand...
Is it surging at wide open throttle under load (while cutting grass)? If not, then run it, or find another shop that can fix it. You can also shorten the spring to throttle that helps control the butterfly, therefore minimizing the surging.


#16

animattor

animattor

Tiger Small Engine said:
Is it surging at wide open throttle under load (while cutting grass)? If not, then run it, or find another shop that can fix it. You can also shorten the spring to throttle that helps control the butterfly, therefore minimizing the surging.
Click to expand...
It started surging while cutting tall grass but still surges at idle. (The video was taken at idle)


#17

G

GearHead36

animattor said:
It started surging while cutting tall grass but still surges at idle. (The video was taken at idle)
Click to expand...
Surging while cutting tall grass? Are you sure that this wasn't just the result of a heavy load on the engine. Patches of tall grass will put a load on the engine, and will cause it to slow down. If you have patches of tall grass, it could seem like a surging engine.

A general recommendation... ALWAYS run your OPE at full throttle. Mowers, trimmers, edgers, chainsaws, etc. All of it. It's ok to run at low throttle for short periods, but the cheap carbs on these engines are tuned for optimum running at full throttle. They will run ok at part throttle, but will cause lots of carbon deposits. With mowers, you should also use full throttle to get the proper airflow through the deck. My push mower is a Toro Recycler with a Briggs flathead engine. It doesn't even have a throttle control. It's always at full throttle. Part of me thinks that running a cold engine at full throttle is hard on it, but it's 13 yrs old, and has never needed a service, other than a governor spring that got destroyed. The carb has never been off the engine, and has never been opened up.


#18

S

slomo

animattor said:
the saga continues. I pulled out mower for the first time this season, and it started right up. cut well, ran smooth for about an hour and then started surging again. Fuel bowl is clean, the float moves freely, and i tried cleaning idle jet with canned air (i don't have anything small enough to try physically unplugging the jet). Fishing line. there is no debris in air intake. I put in 75% fresh fuel (mixed with a little left over from last season). Try dumping, blowing out with shop air, finally confirming the fuel tank is free of debris.

At the end of last season mower was at service and running well.
Here's a video of the surging at idle.
any suggestions appreciated. I'd like to get to the bottom of this. It is still under warranty, but for service, not return. In about 10-12 hours of use it was at service three times last season. Surging is a dirty carb or vacuum leak mostly. Something in the fuel delivery.
Click to expand...


#19

animattor

animattor

I took it back to the mechanic today. He thinks the problem is due to the partially old fuel I used—gummed up something in the carb. Guess I should have just dumped the .5L leftover and saved myself some trouble!


#20

S

slomo

animattor said:
I took it back to the mechanic today. He thinks the problem is due to the partially old fuel I used—gummed up something in the carb. Guess I should have just dumped the .5L leftover and saved myself some trouble!
Click to expand...
Could be.

I always use fuel stabilizer. Why? I forget how old my fuel is. Don't have to worry about old fuel anymore. My fuel doesn't get gummed up.


#21

7394

7394

Use 100% gas.

If I could buy another antique B&S Flathead 22" Pusher, I would. Mine is 18 years old & still cutting like a hot knife thru butter. 1 pull starts.
They don't make em like they used to. (no offense meant)..


#22

animattor

animattor

slomo said:
Could be.

I always use fuel stabilizer. Why? I forget how old my fuel is. Don't have to worry about old fuel anymore. My fuel doesn't get gummed up.
Click to expand...
It looks like the old fuel gummed up the carb. I got some stabilizer from the mechanic when I picked up the mower. Hopefully that will prevent this from happening all the time.


#23

Tiger Small Engine

Tiger Small Engine

7394 said:
Use 100% gas.

If I could buy another antique B&S Flathead 22" Pusher, I would. Mine is 18 years old & still cutting like a hot knife thru butter. 1 pull starts.
They don't make em like they used to. (no offense me)..
Click to expand...
It’s hard to kill a 5 horsepower flathead Briggs engine, and it’s hard to kill a Briggs opposed twin.


#24

7394

7394

Yep, hope I didn't just jinx my 'minnie-mow' (wifes' name) for my pusher. She is the chief operator.


#25

RYANS'

RYANS'

My life I have been mowing. Never bought new mower, I have simpathy for this person. He/she must get money back from a faulty product. For all our sake.


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