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SU Carburetor Installation
The SU carburetors shown above have been returned to me by Keith Williams after a complete cleaning, overhaul, and installation of oil-soaked brass bushings to eliminate air flowing around the throttle shafts, and greatly reduce wear in the future. Their beauty really puts the rest of my engine compartment to shame. Installation was not difficult. The steps outlined below are for a U20 engine. An R16 may be slightly different, but it should be similar. First remove the carburetors and heat shield from the intake manifold. Next make sure the plumbing T on the front of the intake manifold is tight and oriented in the correct position. If you fail to complete this step now you will not be able to turn the T in a complete rotation once the manifold is attached to the head. Now you can mount the intake manifold to the side of the head and torque the nuts down to about 11 Ft. Lbs. Make sure you use the correct heavy washers to bridge the intake and exhaust manifold gaps on the lower row of studs. Install the heat shield. The rear carburetor is mounted next. Once the rear carburetor is mounted mount the front carburetor. Note that the front carburetor linkage to the coupler rod is U shaped. The coupler rod must be inserted inside of the U while at the same time you are placing the linkage shaft ball into its socket and inserting the fuel connection into the fuel hose between the two carburetors. Once both carburetors are mounted install the return springs. The shorter spring is attached to the rear throttle shaft. Mount the fuel and vacuum lines and the drain hoses to the overflow tubes. After you have attached the water hoses and control cables you are finished. I have also included a picture of the maintenance screw, and the fuel return valve. Note the spacing between the two. Once you have completed the installation the maintenance screw is not a throttle idle speed adjustment and should not touch anything. The thing you have to watch out for is contact between the screw head and the fuel return valve as the throttle shaft rotates. If these two make contact you may find yourself dealing with a stuck throttle. In my case that happened as I went through a radar trap. Make sure there is sufficient spacing to prevent this dangerous situation. And yes I had to pay the ticket. On a similar note: The problem of the service screw hitting the "valve return fuel assembly" (as Nissan calls it) came up a few days ago. The problem happens when the float bowl rotates on the mounting bolt. The throttle sticking open is the usual consequence. After looking at several carbs and doing some head scratching I have come up with a fix that I like. Two things are done. First the head of the service screw is reduced in thickness allowing a bit more room. Second, the carb body is drilled and a dowel pin is inserted to limit the rotation of the float bowl. For anyone who has a set of my 2L carbs I will make this modification at no cost. Contact me off list for details. When I did the original refurbishment I returned the carbs to the original Nissan configuration and most of the time there was no problem. A couple of folks did have problems so I am offering this fix. Keith "roadster ranch" Williams
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