Riding mower surging when off choke [video]

[Moshtaraq]

Hi,

I recently picked up a lawn mower that sat for some time. It wouldn't run or start so I ultrasonically cleaned the carb and put new fuel in there. Here is a video of it. On choke it runs smooth, when it goes to half choke, it starts backfiring and when when I back off the choke, it starts fluctuating and it eventually stalls when closing the throttle.

The nikki carb was, as mentioned, cleaned.
Valves checked.
New fuel.
Governor checked.
Plug is black and sooty.

Any advice is welcome!

Excuse my English, I'm Belgian ?

 

[Rivets]

Sounds like you have one of three possible causes for this lean running condition. 1. Main nozzle plugged. Did you remove the main nozzle and jet before you put it in the cleaner? Have seen many times they will not cleaner properly without removing. 2. Did you check that the float height is correct? 3. Have you checked for leaks in the intake manifold and around each mounting gasket? Take a can of carb cleaner and spray all these areas, any change in engine speed would indicate possible leak.

 

[Moshtaraq]

1. Yes I did remove the main jet and put it in the cleaner seperately.
2. Float height can't be adjusted cause it is integral to the float.
3. Tried with a very flammable degreaser and can't hear anything

 

[Rivets]

Really sounds to me like a fuel delivery problem. If you are sure that everything a posted is good, then I would recheck valve clearance. If the valve clearance is good I would reclean the carb and install a rebuild kit. When you post back include all engine numbers.

 

[bertsmobile1]

A make & model number for the mower and engine numbrs for the B & S will go a long way to helping us give you Sound advice rather than general guseeing.
Now if this was a Nikki carb with the white intermediate plate between the body & the bowl I will guess you lost the main jet from the end of the white tube.

 

[Moshtaraq]

I'll get the full model nr tomorrow (mower is at my brothers place). Main jet is in the white tube. Only thing I noticed was that the idle jet is not in this carb but that may be specific for this carb.

 

[Moshtaraq]

Mower is a Castelgarden xf 140 hd
Carb Nikki 799247
B&S 21B807 0138 H1

 

[slomo]

Ultrasonic cleaners are not the end all Holy Grail of carb cleaning. Just as you found out first hand. No replacement for good ol' elbow grease and carb cleaner. Probably need to boil the carb a few times. Obviously some dirt where you can get to inside the carb.

slomo

 

[slomo]

I'll get the full model nr tomorrow (mower is at my brothers place). Main jet is in the white tube. Only thing I noticed was that the idle jet is not in this carb but that may be specific for this carb.

Maybe the pilot jet fell out? Check your engine parts list. See if yours has one.

slomo

 

[slomo]

I recently picked up a lawn mower that sat for some time

Drain and clean the fuel tank.

Sounds like you have 2 things going on, rich and lean conditions. Black plug and surging, needs choke.

Attack the carburetor first.

Plug is black and sooty.

slomo