carburator float

[67hat34c]

I am changing a prior thread with the hopes of a good answer.

I had problem with the little Nikki Carburator on my Onan MCCK. I was able to clean it out and rebuild it but cant figure out the float. The gen is working on my spare which i built and seems to run great. however the float is still an unanswered issue.

The thing is real simple down draft carburator. bowl has a float and a needle valve body with needle in it. the only other opening in the bowl is the high speed jet at the bottom of the bowl. The upper hemi of the carb has a gasket that seals off all other openings as far as i can tell.

So what does the float actualy do? is it a safety to keep gas from filling past the gasket and leaking outside the carb? Doesnt appear it would have any other function. If no other function then it would not appear the setting is all that critical. Just prevent the float from hitting the top of the body before it closes, Right?

 

[MikeP]

Float level is extremely critical for proper operation AND safety.

As a simple explanation, the float ensures that the level of fuel in the bowl stays at the proper level. If it drops too low, there will not be enough fuel to keep the engine running under load. If it is too high, the carb will "flood" the engine with excessive fuel. The float level can usually be adjusted in some way - how that is done will depend on the design of the carb. Some floats, like those on the old Quadrajet Carbs are known to absorb fuel over time and lose a great deal of their bouyancy - lacking sufficient "floatiness" to close the needle valve and thus flooding the engine constantly.

THe needle and seat are equally important - even if the float is fine and the level set, if the needle leaks or sticks, the same problems will occur.

From a safety aspect - if the fuel supply is higher than the carburetor the float, needle and seat MAY be the only thing keeping many gallons of fuel from running into the engine and into the bilge. USCG/ABYC standards require that there be an antisyphon valve in the system if the fuel supply is above the carb which SHOULD prevent this anyway but some folks remove them because they sometimes clog. Removing them is very dangerous for this reason but one can never know what a previous owner may have done.

Check the instructions that came with the rebuild kit or look in an appropriate service manual. There will probably be specific instructions for setting float level and float "drop." Both are critical for proper operation.

 

[67hat34c]

Mike, I just realized how this works. dont want fuel getting as high as the jet discharge into the venturi. level in the mixing tube will be same as in the bowl, duh to me. I suspect i have the float proper in the carb i have at home but the one I installed in the boat is not going to be correct so i will swap them out.

Float level in this case is set by bending prongs the the needle sits in . very basic unit.

 

[31FlyCruzr]

I believe the quadrajet floats Mike is referring to is the black plactic type, the coating can braek down and they absorb fuel. If you have a soldered brass float, never replace it with the plastic version during a rebuild unless you know the float is badly corroded or has fuel inside it from a leak. These are the replacement floats in many kits today and the original brasa are much better

Bill