Briggs and Stratton Carburetor Leak

15 years ago

I have a mower with a Briggs Vanguard 18 HP V-twin (model# 350777, type 1048-E2) engine that has a slow but continuous leak from the carburetor when the engine is NOT running. The gas comes from inside the throat of the carb on the air filter side. Thinking this was due to the float sticking, I pulled the carb and had it rebuilt at a local small eng. repair shop. This included replacing the float needle. After re-assembling, it still has the same leak. The mechanic says this may be due to a bad fuel pump that is letting too much gas through when the engine is off.

I would like to ask if there is some way to check this vacuum fuel pump before shelling out $50 for a new one, When I disconnect the fuel line between the pump and the carb.,a very small but steady stream of gas comes out of the pump until I shut off the valve. If I turn the engine over with the starter, the stream is just a little bit larger and broken into droplets but it doesn't really surge or spurt with the engine strokes like I thought it might. BTW, the engine idles & runs very well at full speed with good power. It's just that I'm tired of killing the grass when I forget to turn off the gas line at the tank when I stop mowing.

Does it sound like the pump is bad or could it be that the carb rebuild job was botched? Or am I missing something else?

Thanks in advance for your help.

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Comments (6)

mownie
15 years ago
Botched job on the carb for sure. I don't know what was botched but the needle valve (and float) is designed to shut off the fuel completely when the specified fuel level is attained in the bowl.........EVEN if the fuel pump is pumping at full volume and pressure. It certainly would be able to resist the very slight pressure availed by mere gravity. It's possible that the float is adjusted wrong or it might even be rubbing against something in the bowl that prevents the needle valve from closing securely.
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gorper99
15 years ago
Find a new shop.I dont rebuild them anymore.I find it is a lot less of a headache just to replace with a new carb.
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***"sitting idle"*** As in "mower is turned off and stored between uses" or as in "sitting there running at idle RPM"? If you mean "while the machine is stored between uses, the carb overflows and drowns the engine, filling the crankcase with oil". This is a very common problem and is a consequence of a gravity fed fuel tank not having a manual shutoff valve to positively block fuel from flowing past a leaky float needle valve in the carb. If this is your problem, you can opt to install an inline fuel cutoff valve in the fuel hose between the tank and the fuel filter (and do nothing further). But then you must learn to ALWAYS shut this valve any time the engine is not running (even if it's just so you can take a break). In most of the cases, the leak past the needle valve is so "small volume" that the normal operation of the engine during use when running will not be affected. Only when the engine is shut off and stored does the small leak turn into a big problem given enough time to leak. Now, if you mean that at idle RPM you see fuel leaking to the open, then you have a defect in the carb float and/or needle valve. And if fuel has been getting into the crankcase lube oil, change the oil and filter (if present) before operating the engine again.
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I realized in my initial thread I wrote after the fuel pump when I meant to say after the fuel FILTER. This engine is model 274844. So a fuel line goes from the fuel filter (the original fuel line comes from the fuel tank under the seat, to the fuel filter) into this round black plastic device, and a vac line goes down from this part into the area where the valve cover is, and another fuel line exits this and goes to the engine. So three lines total, 2 fuel one vacuum. The part just says "ikuni" and "made in japan". I'm sure you're right about bad diaphragm in fuel pump. Where to find the part?
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tomplum
15 years ago
Had you cleaned the fuel system/ replaced the filter? Debris could be the culprit. My best advise is to put an inline fuel valve in and use it. These carbs much of the time do not have a tab on the float to adjust nor a seat to replace. Every so often you need to replace the carb.
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walt2002
15 years ago
"Does it sound like the pump is bad or could it be that the carb rebuild job was botched?"

No to the first part, yes to the second. Sounds like you have a fuel line shut off valve, I would just use it.

Walt Conner
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larryf
15 years ago
There may be some defect in the carburetor (such as a small crack) that is causing the leak. It is also possible the needle seat has a defect and even with a new needle, the seat is responsible for the leak. If the original fuel line was reconnected to the engine, there is a possibility rubber particles from a deteriorated fuel line are entering the carburetor. Since you removed the carbureter yourself, the shop could not verify their repair. I don't know if you can expect them to perform additional repairs.

The vacuum operated fuel pumps supply very little fuel pressure - perhaps only 2-3 inches of pressure. When the engine is shut off, the pressure would drop to zero very quickly. I would not expect a fuel pump problem.

My thoughts are to verify the condition of the entire fuel system by removing the fuel tank for cleaning. I dump all old fuel and spray the tank interior with carburetor spray and allow this to drain in a plastic container. If there is anything left, I draw it out with the Thomas vacuum system. During this process verify the cap is venting so pressure will not build in the tank due to heat. New fuel lines and hose clamps would reduce the possibility of rubber particles entering the carburetor. A new 35 micro fuel filter would trap smaller dirt particles. Allow a little fuel to flow through the system before connecting the fuel line to the carburetor.

The carburetor will probably need to be rebuilt again or replaced.

If you have a fuel tank that is higher than the engine, your best bet is to install a shut off valve.
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chudapucka25_yahoo_com
12 years ago
I have the seem issue with gasoline overflowing carb, Could be the foat is heavy and needs replaced .
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Briggs and Stratton Carburetor Leak

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mownie

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