Hello all, I have a 1967 Evinrude 18hp that I purchased from a guy that had said fuel was pouring out of the back of the carburetor. He had a ton of work previously done on it and it was in great shape, so I got a pretty good deal on it. I took apart the carburetor and figured the float was just out of adjustment. So I put a rebuild kit into it and put it in chem-dep for a couple days and cleaned it up. Everything was pretty clean but it got new gaskets, etc anyways. Even after adjusting the float to an extreme, when you prime the fuel line bulb, gas seems to still be getting by the needle and it comes pouring out of the overflow and the high speed nozzle in the throat of the carburetor. The float floated fine in a jar of gasoline, the needle seat and everything look OK. When I test it by blowing into the fuel input, the float works. I also tried with my air compressor and when you turn the carburetor upside down it cuts off the flow with the needle seated. But when I connect the fuel line and pump gas into it, it just floods the crap out of it and fuel pours out from the overflow and nozzle. I have since ordered a new float assembly, same problem. I have adjusted the crap out of the float, same problem. I have closely inspected the carburetor body and passageways and can't find any cracks or leaks. The needle, needle seat, and needle passageways are clean as a whistle with no debris or imperfections whatsoever. The fuel pump is the original unit and seems to be working just fine. I've rebuilt a ton of these old outboard carburetors and never had a problem, but this one has me stumped. I've replaced every part in the carburetor, and it's still overflowing the bowl. The fuel tank and hose work fine on my 1976 6hp Johnson and 1989 4hp Evinrude. Does anyone have any ideas? Short of buying another carburetor assembly, I'm not sure what else to do.
make absolutely sure that you are using the correct float valve seat and needle valve and not one that might be to big (or small). You could even look at the tip of the float needle valve with a magnifing glass to check for minor imperfections. Unless there is a crack in the carb body somewhere, that float valve is the only way that fuel can go through the carb un-controlled like that. Try using compressed air to blow out the valve seat area and look for damaged threads. Hope this helps you because I'm just guessing here.
Thanks for the ideas. The kit I ordered was a Sierra. I'm going to try ordering the needle and seat kit from OMC and see what happens. Is it possible to tighten the needle seat too much and crush/break the washer and allow gas though like that? I would think with that type of washer gasket under the needle seat, it wouldn't hurt to overtighten it. Should I try a copper crush washer there?