That's what I used to think too, twin carbs must flow twice the air. But then I read the Weber Handbook and found out the without the plenum, they flow nearly the same as a single carburetor (something about 4-cycle engine only having an induction stroke once per two revolutions = 1/rpm with a 4-cylinder).

Also all engines suck the same at idle, around 18-22 inches (unless they are worn out), V8, 6 or 4

Dual Dellorto DHLA40 are too small for A12 when fitted with the smallest venturis (basic tuning parts). But just right for an A12 if fitted with the 27mm ones. And just right for A15 when tuned with 31mm venturis. Nissan New Zealand used 28mm venturis on their round-port A12 with high-RPM camshaft. See Dellorto Tuning for Datsun 1200

Quote:
Quote:
Quote:This is an old question but a common one. The answer may help someone searching ... the Idle circuit is the fuel passages and adjustment valves that allows the engine to idle. It only works at low RPM generally below 1500 RPM

* with single carb, anytime an engine won't idle below 1500 RPM, but will run steady at 2000 RPM or higher, check the idle circuit

* with dual carb, anytime an engine runs on 3 or 2 cylinders below 1500 RPM, but will on all 4 at 2000 RPM or higher, check the idle circuit(s)

Dellorto DHLA idle mixture screws


1. Start engine, let it warm up fully, and let it idle

2. Go to one of the Idle Mixture screws. Count the number of 1/2 turns it takes to screw it in. Use a light touch and don't force the screw tight

* As you screw it in (anti-clockwise) the engine should slow down or even die. That's normal. Back the screw off to the original position

* If the engine does not slow down, even when the screw is all the way in, the idle circuit is is blocked (no fuel is flowing through that side). Congratulations, you've found the problem

3. Repeat for each side of the carburetor

4. Repeat for 2nd carburetor

If you find a 'dead' idle circuit, the carburetor needs cleaning (it doesn't need a kit). Stop the engine, remove the Idle Mixture screw carefully (don't lose the spring parts), then using a can of spray carburetor cleaner, spray straigh down into the passage using the long plastic nozzle of the spray can. Sometimes this is enough to unblock the passage. Replace the screw and start the engine. If the problem still exists, a more thorough cleaning is needed

cheap on fuel

check your idle circuits (I dont know what that means but thats what people told me when mine was doing it)