1994 Mercury 30 hp 2 cylinder flooding, float needle not shutting off.

[Afwjam]

Trying to help a friend get his motor running. It floods spitting fuel out the front of the carb. I have rebuilt the carb, including new needle and float. When the carb is apart and upside down the needle shuts off everytime, when it's on the motor it won't shut off. I have adjusted the float even to extremes and it does not shut off. I can't for the life of me figure out what's going on. Does not seem to be binding on the pivot pin, I polished the seat(non replaceable) and the needle seems to work and shut off smoothly with the bowl off. I'm about ready to order another used carb as its driving me crazy. Can the vaccum pump create to much pressure and blow off the needle? The primer bulb won't get hard and will flood it as well. I'm sure it has to be the float and needle but cannot for the life of me figure out why it's not shutting off. I appreciate any help, I'm a motorcycle mechanic and outboards are new to me. Would rather not throw parts at something that should be so simple.

 

[Afwjam]

Bump for any ideas?

 

[RCO]

Possible the float is hanging up on the gasket?

 

[Texasmark]

Pump only develops a few psi of pressure at high speeds. Considering the area of the needle is like 1/20th an inch in area and the Class 1 lever of the fulcrum to the needle valve distance vs the distance to the rear of the float is 20 or more:1. Very little pressure, like a few grams on the float will seal off the needle valve.

Did you test to see if the float is actually floating? Seems you checked everything else and when you have the bowl off you can't tell whether it is or not. Have to test the float itself in a cup of gasoline. That float is 22 years old. Very well could be saturated.

 

[Silvertip]

Do a simple "blow test" with the bowl off and the carb held in its normal orientation. If you can blow into the fuel inlet with the float hanging, fuel will obviously flow. Now tip the carb upside down and blow into the inlet. If you can still blow into the inlet the needle and seat need replacing or the float is hanging up. Repeat these two tests with the bowl installed. Different results = an assembly or interference problem.

 

[Afwjam]

I thought the pump was to weak to blow it off. When I blow into it with the bowl off it seals great, as hard as I can blow. It's only once the bowl is on that the issue occurs, I've checked all clearances and I see no obvious interference, wish the bowl was clear so I could see what's happening. I replaced the float in desperation, both floats float equally well, no holes in hot water on the the stove or any fuel inside. I'm correct that aside from a real hard squeeze, the bulb should go hard against the float valve and not push fuel through? I've located a set of three carbs off the 90 hp motor on eBay, same part number, looks like all I need to do is tap the side of the carb for the idle adjustment ramp and swap the linkages. With three carbs one has to work, I'm stumped so I'm going to throw parts at it against my better judgement. I hate to replace parts without understanding why. Thanks for the input, any other ideas would be appreciated, I want to know what's happening here.

 

[Texasmark]

My last manual covered 2000 year model area 75 through 125 engines, basically 4 hp values and there must have been 3 pages of carbs listed to fit those 4 groups of engines, all based on 3 or 4 cylinders of the same basic cylinder dimensions and fuel/air flow. Wish you luck on finding something that will work on your engine.