B&S 20HP Issue

[NutzTN]

My V-Twin B&S 20HP ITEK engine starts right up, but under load (belly mower) starts missing and blowing smoke. I pulled the plugs for a gander; the right side is somewhat fouled (I have seen worse) and the left side is very wet. It appears that I am getting too much fuel or have faulty spark plugs.
I removed the cowl and to take a look at the armatures, they are original with the motor and appear to be okay - I would guess that the motor would have a miss in all cases if their was a problem here and not while under load.

Is there something else I should check?

BTW: I previously replaced the air filter, oil filter, and oil. I also checked the fuel tank cap vent hole and air passes freely.

 

[Willl]

A quick compression test could rule in/out that half of the engine.

 

[CharlieS]

were the plugs fuel wet or oil wet?
if you reciently added oil and its over full could cause these symptoms

 

[NutzTN]

Sorry for the delay in responding, I had to leave town on business.

I have not checked compression, but will today.

Oil fill is just under the full mark. New air filter - well about 2 hours of operation.

Spark plug condition: left plug is carbon fouled - not "concrete color" but fires good spark; right plug is clean but "fuel" wet and fires good spark.

I removed the carb and fould the crankcase breather hose cracked, but the flap valve in the breather was not clogged and operated freely - not sure if the cracked hose contributed to this problem. I did notice that the intake bolts were not as tight as I would have thought.
Can someone tell me what the torque rating should be on the intake manifold bolts - can't be much since the intake is plastic?


The motor ran great at prior operation, no smoke, plenty of power, no unusual noises, and started normally. Then sat for a week in the shed.

Funny thing; I just rebuilt the K46 tranny and it works flawlessly, all safeties function as they should and the battery is in good shape.

Again I am sorry for the delay in responding.

Follow Up: Did a compression test 155 both cylinders (cold)

 

[NutzTN]

I believe that I have found the problem, but I will not know for sure until a $3.00 o-ring arrives. After changing out the Autolite plugs for B&S, the engine ran better but fouled again as soon as I engaged the belly mower. Black smoke out one cylinder; disengage the belly mower and the the smoke clears but an intermitent miss still can be heard at idle. This leads me to believe that the problem is with the Nikki two barrel carb; operating way too rich. I removed the carb and found all the air passages to be clear. The "single" jet at the base of the float bowl is just above the fuel solenoid shut-off. It has an o-ring that seals the end of the fuel transfer tube which is normally submerged in the float bowl. Inside each side of the double barrel transfer tube is a single air mixing tube that meters air based on engine vacuum. Under no load, the vacuum is low and air metering is nearer the correct ratio, but under heavier load the govenor opens the throttle increasing the vacuum to provide more fuel and air to the engine. I suspect that this o-ring that seals the transfer tube is leaking. [Probably due to the PO using ethanol gas mixture] Excess fuel must be bypassing the jet to cause the rich mixture and this o-ring is the only place within the carb that can happen.

I will follow up if this o-ring solves this problem.
BTW: A new Nikki carb is $140 plus tax.

Mike

 

[NutzTN]

The O-ring did the trick.