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Discussion Starter #1
I built a hovercraft that uses a 6hp Briggs lawnmower engine (12H807-1756-E1) to power a 24" fan that lifts it off the ground/water. (the hovercraft looks like a Delorean! search "delorean hovercraft" on google to see more). Here's my problem:

6hp Briggs lift engine starts fine when I pull the craft out of the garage (usually 50-70 degree California weather), but after hovering on the San Francisco Bay (salt water) for a while, if I turn off the lift engine and float for a few minutes, when I try to re-start the lift engine, it often has a hard time re-starting. The electric starter will turn the fan, but the engine won't start. I'll hold the key in the start position for 10 seconds at a time (or so) and I'll start thinking something is seriously wrong. But on the second or third or fourth try, after many seconds of holding the key, the engine will finally start, but very slowly, like "putt............................. putt................... putt............. putt.......... putt..... putt.... putt... putt.. putt.. putt." Maybe half the time, it will start relatively quickly - on the first or second try (but never as quickly as it starts when the engine is cold and dry). But about half the time, it just won't start for a while, then starts very slowly.

This happens even with a freshly cleaned carburetor.

Relevant engine info:

Fuel system: Facet electric pulse fuel pump. Fuel shut off valve down-line from that so I can restrict the flow a little bit so the fuel pump doesn't overpower the carb. Regular unleaded gas with Briggs and Stratton small engine fuel stabilizer.

K&N air filter. home-made snorkel pulls dry air from under the hood for the air intake, but I suspect some saltwater could be getting in around the edges (a lot of salt spray comes up from under the hovercraft and rains down on the engine while it's running. Like a gentle, misting rain)

The engine is covered from the salt spray. A separate snorkel tube brings dry air from the cockpit to the engine, above the flywheel (I'm not sure if this works to suck dry air under the engine cover, but I had a oil temp gauge installed for a while and the engine was running at normal temperatures, so I think the air cooling is working fine).
(I tried to post photos, but I can't until I've made 5 posts or more. I'll try later)

Any ideas on what is going wrong? Could it be salt water getting on ignition electronics? or water in the air intake? Or maybe a fuel problem?

Thanks!
 

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This is just a guess, but perhaps it is flooding. When you turn off the engine and float for a few minutes, do you also turn off the fuel shut off valve.

Also, you mentioned that you have a fuel shut off valve so that you can restrict the fuel flow so that the pump doesn't over power the carb. I have never seen a fuel pump over power a carb unless the inlet needle on the carb was leaking. Did you install this shut off valve and what exactly was/is happening with this "overpowering" of the carb?

Again, if the motor was flooding, you will get a lot of cranking before it starts, if it even does start, until that extra fuel is blown out of the combustion chamber.
 

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Discussion Starter #3
ok, thanks for the tip! If it is flooding, what would the solution be?

The fuel shut-off valve is a standard plastic Briggs and Stratton valve, I installed it myself. I use it to close the fuel line if I'm taking the engine out. The engine that I'm having a problem with is made to be used with a gravity feed tank. I was told that some fuel pumps can overpower these carbs, I'm not sure how that works, though. But the fuel pressure from my fuel pump seems pretty close to what it would be from a gravity feed tank, so I'm not really worried about that.

This is just a guess, but perhaps it is flooding. When you turn off the engine and float for a few minutes, do you also turn off the fuel shut off valve.

Also, you mentioned that you have a fuel shut off valve so that you can restrict the fuel flow so that the pump doesn't over power the carb. I have never seen a fuel pump over power a carb unless the inlet needle on the carb was leaking. Did you install this shut off valve and what exactly was/is happening with this "overpowering" of the carb?

Again, if the motor was flooding, you will get a lot of cranking before it starts, if it even does start, until that extra fuel is blown out of the combustion chamber.
 

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How are you shutting it off kill switch, a key, using the valve to lean it out like an airplane. I only ask cause maybe the fuel pump runs a little longer than the motor does thus flooding the engine out.
 

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Discussion Starter #5
well, the fuel pump is run off the accessories circuits of both engines (two engines, two key switches, one fuel pump that is on when either of the key switches is in the 'start' or 'run' position). I'm not sure what you mean by "using the valve to lean it out like an airplane". Someone else suggested that I should lower the throttle and let it idle before killing the engine. Is that what you mean? Also, maybe turning off the thrust engine before I turn off this lift engine would help, since if I do it the other way around, the fuel pump will still be running after I shut off the lift engine.

How are you shutting it off kill switch, a key, using the valve to lean it out like an airplane. I only ask cause maybe the fuel pump runs a little longer than the motor does thus flooding the engine out.
 

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I think it has to do with the conditions at hand, rather than whether or not the engine is cold/hot or has salt spray on it. Sounds like it's flooding, and probably is a result of the waves bouncing you and the craft around whilst you're floating.

As turning the fuel off when shutting down the engine could still permit some flooding with what's in the fuel bowl and lines, as Shocker36 says above, cut the fuel to cut the engine - idle down the engine, turn the fuel valve closed and when it quits turn the key off. When you go to re-start it, give it a few seconds after opening the valve for the system to re-fill.
 
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