Carburetor Repair Question and Answer


Question: My R2 carb is flooding. I reset the float levels and turned the idle adjustment screw. The carb is still running rich. What can I do to fix this?


Answer: Make sure the needle and seat are sealing. Make sure a new gasket is under the seat and the seat is properly tightened down. Use a large enough flat screw driver to hit both notches on the brass needle seat. Make sure there is no nick on the metal needle point where it seats or any ridge on the brass seat.


Mouth blowing through the fuel inlet is not usually an accurate indication of fuel pressure. At least, 3 lbs of pressure, but no more than 7 lbs will give you a reading closer to actual operating conditions.


*Check your carb jet numbers to be sure they are the right ones for your engine and altitude. Check the main metering rods, these also have to be the right number for your jets.


Online source for carb specs: http://www.vs57.com/carb.htm


*Check the step-up springs for the metering rods. If they are too stiff, the carb will run rich, because the rods won’t properly pull down under normal high vacuum conditions.


*Make sure the step-up rod pistons move freely and are not worn out. If they are worn, vacuum will not pull these down, either.


*Check the vent holes above rod piston bore to be sure they are not clogged. These are located to the inside of the air horn on the R2 carb.


*Check your floats. To do this, fill a microwave safe bowl with water. Heat the water to near boiling. Remove the bowl from microwave. Place brass float into hot water in bowl and hold submerged. (Do not use your bare hands to do this. Use a pair of needle nose pliers or you will be cursing me). The air will heat up inside the float and any float leaks will produce air bubbling. You’ll then know if you need to get new floats.


Under supercharger high boost, the floats will sometimes collapse and leak. If your floats leak and they become gas filled, they will be sinkers, causing your carb to flood.


*Another thing to check when the carb is running rich is the idle compensation valve located above secondary venturi openings. This valve should be seated when carb is cold.


Today’s gas is so volatile that fumes will cause a carb to run rich. When the valve gets hot, it opens to allow extra air (and gas fumes) to enter the carb to lean out the mixture. By using a thicker base gasket under the entire carb assembly, this will insulate, cutting down on heat transfer and reducing gas boil which causes fumes. I recommend using a 1/4″ thick gasket, rather than what is supplied in a normal stock carb rebuild kit. You can get this thicker gasket from most larger supply Stude vendors.


Also, on R2 engine intake manifolds, one intake gasket is supposed to block off the heat riser port (center port). There will be a half inch opening on the second intake gasket on the center port. This restricts the hot exhaust gases, helping to prevent excess heat soak in the carb.


*Check your heat riser valve on the passenger side exhaust to be sure it moves freely and the spring is hooked up correctly – closed when cold – open when hot.


*For good descriptions of carb circuits and their functions, again, go back to those good old shop manuals. They hold a wealth of correct information.


….and remember, every engine performance is different. You may have to fiddle with rods, jets and springs combination for a while to find the right set-up for your Studebaker.


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