Hello! New member here.
 
I have a Craftsman riding mower with a Briggs & Stratton 331877-1234-B1 (21.5 HP) engine. It just recently developed a severe problem out of nowhere (just happened one day when trying to start it up cold) where it is getting drenched in fuel (and possibly oil too, not sure) and chokes out moments after starting up; smoking and spewing fuel out the exhaust. I believe the fuel/oil is coming from the breather tube.
 
I've rebuilt the carb, and even just replaced the whole carb. It has new fuel line up to the pump. The pump seems to work fine and the fuel filter seems to be just fine also.
 
Does this mean I have a blown head gasket? What else might it be? What else can I do to troubleshoot?
 
Thanks!
Jason Haymond

The NIKKI carbs are notorius for leaking fuel.  Most have a very small o-ring that goes between the main white plastic part and aluminum carb body. If pinched/missing it WILL leak and flood the engine
 
I would replace the carb with the Ruixing:
https://www.partstree.com/models/331877-1234-b1-briggs-stratton-vertical-engine/carburetor-nikki-ruixing-fuel-supply-gasket-set-carburetor-nikki-ruixing-3/ 
 
Before replacing, you can remove bolts from the intake manifold to the head.  Leave the fuel line hooked up and turned on.  Now watch for any fuel dripping out (and would have gone into the engine)..
 
 
Advise..

 

@SRTsFZ6,
 
Thanks for the tips. The carb I cleaned and rebuilt (partially) was the NIKKI. I replaced it today with the Ruixing carb and only a very small improvement, virtually no change. I didn't adjust the new carb at all though. Could that be needed?
 

Ok, if not much help, try disconnecting the crankcase vent hose from the intake track & 
see what happens..
 
 
.

Thanks. I'll try that this afternoon.

When you say "only a very small improvement" are you looking at it from the amount of oil and smoke out of the exhaust? If the muffler had oil spit into it, it will take a while for it to burn off, so looking at the exhaust for too short a time will make it look like there's little improvement.
 
I would, in addition to what's already been said, suggest you take a look at the engine oil. Is it very thin and seems to be too much? That might have happened if the float valve didn't cut off the fuel flow and the fuel kept flowing (because of gravity) even with the engine off. The fuel might dribble into the cylinder, through the rings, and end up in the crankcase, diluting the oil. If that indeed happened, you'll need to change the oil right away.

Thanks for the notes. I was referring to the engine running a bit longer before choking out. It wouldn't run at all before. Only try like with starting fluid and no fuel.

I'll take a close look tonight and give an update.

Alright, I tried unplugging the breather tube from the carb, and now as I expected when running (which it does now, though still with a bit of smoke), there is fuel with some oil literally gushing out the tube.

I'm less familiar with everything that could cause this but it seems to me that would be a gasket blown somewhere. Although, where and what gasket could be holding back that much fuel? I know something major blew to cause this, but I'm still a bit mystified as to what the cause would be without tearing it apart.

I don't think I mind tearing it apart but I'd like to have some idea going into it where to look for problems.

Anyway, thanks for you help guys!

I think it's coming from the crankcase, and my guess is, as I said before, that the crankcase is over-full with a mixture of oil and gasoline. Please check the level of the oil and whether it's very thin. It's simple enough to rule out, isn't it?