Excess gasoline

Good morning forum.

I have a 1975 suburban, from the GMC, to which a 2 throats from 2 throats to economize gasoline was adapted. In general it works well but even with new spark plugs every certain time wet the spark plugs with gasoline, approx every 2 months or sometimes a little more. No oil pass, they already checked the coil in case it was a lack of current, the engine has a few years that ring approxly 4 years. By chance we realized that the passage of gasoline is exaggerated from the tank to the carburated and returns most of the tank so we think the problem is the excess gas that passes through the carburetor, I suck a gallon with 5 liters of gasoline in less than 2 minutes, but because that exaggerated amount of gasoline can be? They have seen several mechanics and have not solved the problem. Any idea?

Check the carburetor float, the deposit may be filled, the float is not regulating well.