how to determine float height 1990 mercury 9.9 2 stroke

[j_reed]

I see from the manual its supposed to be 1" but the measurement is from where to where???? In most vehicles I have dealt with the measurement is from the side/lip of the carb where the bowl attaches, but, I have this answer from the forum, could someone expound on it? "measurement for float bowl is from bottom of the casting that the bowl is bolted to, to the top of the float"
is it just me? bottom of the casting is not that clear. I assume it means the not the rim.... thanks. -j

ps. this is the carb style where the float is not attached to a hinged arm... it just rests against that arm
1990 mercury 9.9 2 stroke

 

[Texasmark]

I have used a rule of thumb over the years and hasn't failed me yet:

Remove the carburetor from the engine and the bowl from the carburetor. Turn the carb upside down. Look at the carb casting where it mates to the bowl, that flat cast aluminum flange. Look at the float. Is the float body parallel to that surface with just the weight of the float determining the height? If it is, you are good to go. If it is up on the far end (the end opposite the needle valve end is positioned away from the carb casting) then the float will shut off the needle valve prematurely and you will have inadequate fuel in the bowl for surge requirements and full throttle operation.

If it's the opposite where the far end is closer to the carb housing, then you will let too much fuel into the carb and it may not shut off the needle valvce at all causing flooding of the engine and fuel running out of the carb venturi when the engine is tilted up.

 

[j_reed]

Texas Mark, thanks for the reply, is this a universal outboard carb thing??? I know for the 1990 mercury 9.9, the adjustment is supposed to be 1" from the???, like I said, to me, the book isn't clear where to measure from, thats been my question, so you are saying from the lip where the bowl attaches?... if that is the case, the carb I have is def off, the other guy I read said "from bottom of the casting" which sounds different... I just went thru a similar adventure with a hard starting honda xr250 dirtbike.... everyone said that for the sister vehicle, the xr400, to turn the carb upside down and level the bowl... as it turns out the float spec for the xr250 actually needs the float to allow more fuel into the bowl than that (south of level when turned upside down)... in that case it really helped the hard starting problem... more fuel in the bowl = more Venturi (gas spray)
-jay

 

[Texasmark]

Let's apply some common sense.

Turn the carb upright. The bowl dangles opening the needle valve and allowing fuel in. Imagine the bowl filling with fuel and the float floating on it. Since the float floats, the float height (sitting on top of the rising fuel level) will have to be added to the fuel height to get the height of the top of the float when advancing up and approaching the carb casting....thus stopping it. This is as far as it can go. If the float hasn't shut off the needle valve (really somewhat before this time) to stop the gas flow by then, gas will continue to flow causing the bowl to completely fill and gas to flow out the vent tube and into the venturi, flooding the engine and dribbling gas on the inside of the cowling.

If it (the bowl) is adjusted too low, the float will ride up the rising fuel and shut off the level of gas in the carb prematurely meaning that there is a low fuel level in the bowl. Obviously the faster you use the fuel out of the bowl, the faster it needs to be replenished meaning that it needs to open early as the gas level drops to get some new gas flowing into the bowl before it uses all that's contained therein.

The adjustment is the flat brass arm between the float and the part of the arm that contacts the end of the valve. Some you bend the arm others you bend a little tab part of it. Easy to see by looking at what touches the end of the needle as you move the float (with your finger or turning upside down) toward the full position.

On "is this a common setting" sort of thing I mentioned, yes. So turn the bowl upside down and look at the position of the float. Is it parallel to the aluminum casting flange where the bowl mates? If so, fine. If not bend the little tab or the flat arm attaching the bowl till it is. Obviously when adjusted like that there needs to be some room between the float body and the casting where the float can rise a little more when the rising gas level (in normal operation) puts pressure on it to force the needle valve to seal.

 

[j_reed]

mark
thanks for the detailed answer... I mostly was looking for where to measure from using the factory spec of 1 inch... when I had the carb apart last and measured from the lip (or casting flange where the bowl mates) to the bottom of the float, the mearument was quite a bit off, more like 1+3/8th of an inch, so far off and with the vagueness of the book, I wasn't sure I was measuring from the rigth place. hence this question... I did not change if from where it was set pending more informantion. though sounds like you don't measure, and just go with level when upside down. thanks for your time and help. -j

finally I should add that while the outboard runs, it doesn't want to idle and stalls unless you activate the enrichment circuit or have the idle way up...while I don't think the float level is affecting/ influencing the problem, next time I have it apart I'd like to set it correctly to eliminate it for sure.

 

[Texasmark]

Since you have the carb out, with the bowl off, did you see any signs of varnish?

 

[j_reed]

so I did reset the float to 1" as the manual stated.... 1990 mercury 9.9 2 stroke

the real problem with the outboard was the reed valve.... it was the original unit, it seems that it was a defective part from mercury and they have since upgraded the design and part number.... I believe others had the same problem, basically what I think was happening is that a rubber gasket on the inside and middle of the reed valve stretches and loosens and flops around effectively blocking or at least disrupts the flow of fuel from the "reed flappers". I was stumped and really only replaced it out of desperation as the reeds showed none of the classic "bad" signs, ie. spitting back fuel,

I had been thru the carb 4 times and it was driving me nuts... any way, its running great, purring like a kitten.

"while the outboard runs, it doesn't want to idle and stalls unless you activate the enrichment circuit or have the idle way up...while I don't think the float level is affecting/ influencing the problem, next time I have it apart I'd like to set it correctly to eliminate it for sure".