carb overflow

green dream machine said:

i have a john deere 11 with a 12hp briggs motor and it floods the motor with gas when i shut it off so i put a shut off valve in it but by the time i get to it it has dumped gas into the crankcase. is this a problem with these carbs or do i nreed to rebuild the carb.and will that help?

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Clean or rebuild the carb. Most likely problem is something is either stuck in the needle/seat or one or the other has wear or damage. You could conceivably have a "sunk" float also, but that's pretty uncommon. If the needle can't close the passage, fuel will just continue to flow until the tank is empty and/or the crankcase is full.

I would bet on a defective float or one that is misadjusted. An easy way to get around it is to put the fuel shutoff valve so you can reach it from your seat and turn it off before you turn the ignition off. That's effectively what Kawasaki did with their solenoid fuel cutoff valve when you turn the ignition off.

I had a similar issue, actually the same issue, with a Briggs engine 2 months ago. If the float is not working or the needle valve is stuck open fuel will continue to flow. And not only will it continue to flow, but because of the way most Briggs small carburetors are designed, with a vent to the crankcase, the fuel will fill the crankcase mixing with the oil.

The first clue will be very large clouds of smoke if you can get it started. A fuel shutoff is not the cure. Replace the carb and replace the oil. Keep checking the oil for about a month until you are sure that the problem is resolved.

First, shut off the fuel and run the motor until the carb is empty and the engine stops.
Then open the fuel and start normally.
9 times out of 10, that solves the problem.
If that doesn't work, you need to take the carb apart and clean the needle/seat.
I've seen many illustrations in books of how a worn out needle looks; but never seen a worn out needle in my life. Just clean it out with compressed air or carb cleaner.

The OP can go crazy with a rebuild, due to what is probably a gummed up carb, or buy a carb on Amazon for about $50 or less. The problem will be that he will never clear all of the passages of gum or hardened residue. The last B&S carb I bought was for a generator and it cost $31. That was after I wasted my time and the cost of a rebuild kit. So the OP can attempt to clean the carb, but after that I wouldn't waste my time any further.

I've never seen a carb that was so bad it couldn't be cleaned. And I've torn apart hundreds. Regarding wear on the needle and/or seat - I haven't seen that either. But it's not wear that needs to be worried about, it's corrosion/oxidation.

If even a little of the tapered part of the needle corrodes away in the right spot it will not seal fluid-tight. The other issue I commonly see is a bit of oxidation sticking the needle open - usually this happens where the body of the needle is supposed to slide freely inside the bore in the carb and they get sort of "glued" together. The problem with just cleaning in that situation is that once the corrosion has happened once, it comes back easier and faster the next time. Best to just get the rebuild kit. If you can find a carb that you're SURE is new for a good price that will work too. If you're buying a rebuilt carb you might just as well rebuild your own.

Edit: I should have more properly said I haven't seen needle/seat wear that actually caused leakage. I've definitely seen needles with pretty big grooves worn in them. The thing is, they seem to wear with the seat into a perfect match, so they rarely leak much even when they're pretty worn.

I've worked on small engines since the early 60's and have seen plenty of carburetors not worth the effort to rebuild. Why charge the customer for a rebuild when you can supply a new carb for almost, and today for even less than, the cost of a rebuild. Time is money son, to both you, the customer, or even just to yourself.

I too have worked on small engines since the early 60's and have seen worn needle and seats as well as carbs too far gone to rebuild. It's rare but more likely now days due to the ethanol in our gas and the low expectations of manufactured products. Young and old alike don't expect their purchases to last anymore so they just don't do the maintenance. Is it advertising and marketing telling you new is better? I'd guess. Now can anyone explain the phrase I heard the other day? My young neighbor said her friend was getting divorced, no big deal, it was just a "starter marriage!"

took the carb off and it was full of rust, crap, ect. cleaned it real good. couldn't get the main jet out so i cleaned everything real good and it works for now. think i will try for a new used carb. it is an old machine from the '80s that was repowered right after st Helens blew. they put a 12.5 hp Briggs in it. it is kinda small but it does the job. now if only i could figure out the height control it is all loose. i bought a spare 111 fo parts the other day so i can look at it. i have already used the spare for brakes, now they work. and the throttle controls that broke on the original came off the spare that spare was the best 50 bucks i ever spent. more updates as i get them. oh yeah, i hooked the alternater up yesterday now my battery charges, it hasen't done that in years.