The car is almost there and i thought you might like a picture of the engine bay, complete with the Mikuni carbs you supplied. The oil acts as a damper, like a schock absorber. If there is an air leak, the rpms will rise or fall depending on the size of the leak, the adjustment of the carb, and the type of aerosol spray. No oil in the dome, the piston has too little resistance to rising and allows too much fuel in too quickly, flooding the engine. I also found it difficult to actually see the fuel meniscus in the jet and found a good method was to use a sliver of a paper tissue as a test strip.
Turn the allen wrench clockwise to richen it. Use the oil sparingly as too muck oil is just as bad as not enough. Areas the leaks most commonly occur are: Step 6 - Check coarse throttle adjustments- make sure the throttle cable pulls on both carbs equally, and returns completly when released. I put this thing together a year ago. All further adjustments to idle speed will be made again with the spring loaded screw. Start with the choke in the off position knob in.
Weber CARBURETOR SET UP AND LEAN BEST IDLE ADJUSTMENT
Then when it's together yo go for the adjustments. With a can of aerosol carburetor cleaner, spray into areas where leaks are found while the engine is idling. Turn the allen wrench anti clockwise to lean it out. Designed to replace SU and ZS carbs they are a simple replacement for those carbs and are one of the few easily bolted on upgrades that produce a signficant, surprising and easily documented, increase in performance with no other modifications. Are the carburetors clean? Carb jetting or adjustment? Despite all the assurances of the manufacturer that this single carb could lessen emissions, the Zenith often runs dramatically rich.
Information should be available via Internet websites. After moving a jet nut, push up on the bottom of the jet assembly to insure that the needle has indeed moved upward. I believe that he is using the 7. When fuel is fed into the float chamber it rises and the float shuts off the needle valve. So now I have to wade into needles. The rear carb is especally frustrating. Once the mixture is set at idle, it will automatically be correct throughout the engine's operating range.