View Full Version : 9.9 Four Stroke Mercury Carb problem
A friend left the fuel line connected and the vent on his gas tank closed on his 1999 9.9hp four stroke Mercury for one week. Since this is a small boat and it is left outside, I'm guessing that the pressure built up in the fuel system due to the hot sun and blew out his carb. The motor ran perfect one week ago on the last trip.
He went out to start the motor and couldn't even pull the cord. We checked the oil and found lots of gas in it. Then we pulled the plugs and found that the bottom cylinder was full of gas. After cleaning this out, the engine can be turned over, but when the gas line is attached and the bulb pumped, gas pours out of the top of the carb.
Time for a full rebuild or is there something less major that can be done to fix this problem?
Your float is stuck? Try tapping the carb.
Rebuild is simple, so you might just want to go for it. 1 hour out and back in.
MattPark
08-27-2006, 02:06 AM
There's nothing you can really "blow out" on a carb like that.
Tap the carb to jiggle the float shut, throw a plug in, change the oil, and pull till she starts. Run for a few minutes, then change the oil again. If the oil smells like fuel still, change it again (not like it really costs anything anyways). The whole engine was flooded with fuel. No big deal, just get the fuel out of places it shouldn't be.
Remember to shut the fuel off next time.
Starfish
08-27-2006, 09:21 AM
:yeahthat:
Only thing I'd suggest different than MattPark is that you might want to open the carb bowl and pull off the float and give it a shake to ensure it didn't get filled with gasoline. If there was a pinhole leak in the float it might have gotten filled and may no longer work. Replace it if there's any sign of liquid inside the float.
Drain/replace all the fluids, leave the plugs out and fuel disconnected while turning over the motor a while to blow everything out, then reinstall plugs and give it a try. Be sure to wait until the worst of the gasoline fumes have gone away before attempting to start so you don't cause a fireball.
You guys were right! Stuck float. I should have thought of it. A couple taps and everything is okay. Changed oil once but need to do again now that it is running. Thanks for the help! Wonder how much this simple fix would have cost at a dealer.....
Chrome Bumper
08-29-2006, 09:30 AM
You guys were right! Stuck float. I should have thought of it. A couple taps and everything is okay. Changed oil once but need to do again now that it is running. Thanks for the help! Wonder how much this simple fix would have cost at a dealer.....
I'm geussing the Boat Doc' would have set you back a shop hour or two after a coupla oil changes and a good carb cleaning. There would be a lot of shops who would find a bad engine block or something.
Don't know what it's been with the newer 9.9 four strokes mercs but this has been a on going problem I think they are useins the plastic needle valves and if any dirt or debre gets in to that valve seat it seems to really plug them up, took mine apart and found stuff i couldn't believe how it got inthere in the first place,cleaned out the float valve and ran like knew, this sort of thing is one of manny i've heard of, something going on??????
MattPark
08-29-2006, 11:48 AM
Do they have any kind of filter between the tank and the carb? I assume they are gravity fed?
If not, you can get a little clear inline filter at a motorcycle shop or something for a buck or two, I would think it would take care of the problem.
Reel Knotty
09-03-2006, 06:54 PM
My 9.9 4st merc did something similar...when I would start the motor, it would puke gas out the carb and run, really, really rich and foul plugs badly. Of course I was up at Odell lake when it happened :eek: I took it off, took it apart, found crap on the needle and all sorts of gunk in the carb.
I don't know how this stuff is getting in there...have a spin on filter plus a small inline the gas goes through before hitting the carb.
Put it back together and it ran great :wave:...so far, so good. Am planning to rebuild the carb this winter.