17.5 hp Briggs Intek hydro lock

I have a single cylinder Briggs 17.5 hp, 31C707-0154. Fuel is running into the cylinder when it sits and it will cause it to hydro lock when trying to cold start.

I have rebuilt the carb. I've checked that the fuel cutoff solenoid is working properly. I replaced the main jet where the fuel solenoid seats. I replaced the bowl and the needle valve. It has a metal valve seat that I have not replaced, it looks fine and has not been tampered with. I can hold the carb upside down and the needle valve will seat properly and cut off any air pushed through it. The float seats level. I am using the correct new bowl gasket.

Anything else I should check? There is no fuel pump, it's gravity fed. I haven't checked but I'm assuming it is not supposed to have a fuel pump, if so it was removed.

arch252 said:

I have a single cylinder Briggs 17.5 hp, 31C707-0154. Fuel is running into the cylinder when it sits and it will cause it to hydro lock when trying to cold start.

I have rebuilt the carb. I've checked that the fuel cutoff solenoid is working properly. I replaced the main jet where the fuel solenoid seats. I replaced the bowl and the needle valve. It has a metal valve seat that I have not replaced, it looks fine and has not been tampered with. I can hold the carb upside down and the needle valve will seat properly and cut off any air pushed through it. The float seats level. I am using the correct new bowl gasket.

Anything else I should check? There is no fuel pump, it's gravity fed. I haven't checked but I'm assuming it is not supposed to have a fuel pump, if so it was removed.

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I had a 14HP Kohler engine on a Snapper that did this. I think it had a Walbro carburetor.

What baffled me was shouldn't fuel run out the fuel bowel vent and onto the ground instead? Normally if a float valve is leaking, fuel will just run out the vent and all over the ground. Not fill the entire crankcase and cylinder up with gasoline! Actually, seems like I could not find a fuel bowel vent on this carburetor. Maybe it vents back into the intake manifold?

My engine got an enema about three times before I finally fixed it!

I replaced the float valve, then the float valve seat and it still hydro-locked. I ended up putting one of those manual fuel shutoff valves on it and never had any more problems. Unless of course I forgot to turn it off! But I took one more step to remedy that. I'm sure this will not be recommended by others.

I drilled either a 1/16" or 1/32" hole in the base of the intake manifold between the air cleaner and carburetor. My theory was if I forgot to shut the manual valve off, fuel would run out this hole instead of into the engine. I tested it one day and it seemed to work.

Despite the fact I normally kick up quite a dust bowel mowing, I can't imagine enough dirt would get through a 1/16" or 1/32" hole to do much damage.

BTW, I have the same 17.5 Intek engine on my Troy Bilt and seem to think there is a manual shut off valve on it that came from the factory.

All it takes is a small nick or burr on the seat and it will not seal. Also the bowl vent is internal to the carb. It is the larger hole located on the side of the venturi on the air cleaner side of the carb. If that gets clogged for some reason will cause siphoning. Rare but cold happen. Stale fuel and leaking float valves are the two most common issue with todays carbs. Have to to replace carb for that exact reason because the seat wasn't replaceable. And have seen problems with new seats also.

Have used valve lapping compound on the end of the old seat or sometimes on the end of a Q-tip to clean and remove any burrs. Sometimes works sometimes not,

I too have suffered this same oddity .... my crankcase had gas / dilution .... installed a fuel shut-off valve and that APPEARS to have solved my problem ( as long as I remember to shut it off ) as stated elsewhere ... it seems the problem is very common to the Briggs 17.5 HP engines with this Nikki carburetor on them ... check your oil level before starting n take a sniff if its over full mark....engine may appear to have a dead or weak battery/ start solenoid BUT ... rotate flywheel by hand to check for hydro-lock.... :confused2: .... Boobala

I have a fuel shutoff valve installed but I have fixed this one to sell so it needs to be right. It's near impossible to find a manual for a Briggs that's installed on a Murray. I've found a fuel pump part number for that engine, just not sure if they all have fuel pumps or just certain engine codes. I haven't checked the crankcase to see if there is a vent that has been plugged off that should go to a fuel pump, I'll check that tomorrow. I have a sneaking suspicion this might have originally had a fuel pump and it went bad so someone removed it and relied on gravity feed.

Briggs doesn't show fuel pump for that engine according to parts diagram.

I guess I can rule that out.

ILENGINE said:

Briggs doesn't show fuel pump for that engine according to parts diagram.

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I agree , this engiine ..... in every instance I've run across , does NOT use a fuel pump !
I tied a short bright orange ribbon on my steering wheel to remind myself to shut-off the the fuel valve and run the engine till it dies from lack of fuel when I'm done mowing . Now if I can remember why that orange ribbon is on the steering wheel ... ( LOL ) I'll be alright !! ... ..:laughing:

As said, a manual fuel shut off is best insurance, IF you don't want to do that or are afraid you will forget, you can get an electric one for around $20, cheaper than a new engine. OP mentioned carb solenoid is working, that has nothing at all to do with your problem. Both B&S carbs have very small floats and so put little pressure on the float needle. Some say ethanol causes small flecks to flake off the inside of the fuel line and will keep the float from seating. Replacing fuel line may help.

As for fuel draining out the vent, EPA put an end to that years ago. Engine used to have a drain hole drilled between the carb and air filter to drain fuel IF the float failed. EPA put an end to that too. That drain did have a sort of filter and I would certainly recommend having some sort of filter as well as not advertising what you are doing, EPA again.

Walt Conner

Don't you just love it when the EPA get's involved with stuff. Newer carburators don't even have an idle mixture screw! I guess eventually if it get's to the point the engine won't idle properly, you have to get a new carburetor. But looks to me like it would make more sense to be able to adjust it than letting the engine run with an improper fuel mixture. Of course these people are not mechanical engineers but lawmakers so they don't have a clue to begin with.

My Trabant has a gravity feed fuel system and came with a petcock valve under the dashboard with reserve mode. If I forgot to turn it on, I'd make it about half a mile then the car would die. If I forgot to shut it off, the float valve might leak and dump a bunch of fuel out of the weep hole mounted on the elbow between the carb and air cleaner. This weep hole is there to prevent the engine from hydrolocking if you forgot to shut the valve off and has a small hose that runs to the ground away from the alternator. So basically I did the same thing on my Kohler engine by drilling a small hole in the pipe between the air cleaner and carburetor.



I installed a fuel solenoid shutoff valve (the brass device) connected to the coil so when I turn the ignition on, it automatically opens the valve.

Ignore that see through fuel filter. It's now gone because it started leaking.