Weber DCOE sidedraft carburetor. The traditional racing carburetor.
Contents |
Sizing
Proper sizing is important for good performance:
For a 1200cc engine at 6000 rpm, with a single carburetor it looks like a 26mm venturi is called for, based on this chart and interpolating for 6000 rpm based on the DCOE chart.
Now, looking at the A12 specs, it seems Nissan used the same logic: A12 venturi: 26 mm
See main article: Carburetor Sizing
For dual-carburetors (one barrel per engine cylinder) 28mm venturis are called for. In A12 practice that means 27mm for totally stock engine for maximum flexibility or 29mm for maximum power with little less flexibility. Flexibility means good response at all RPMs with no flat spots or rough transitions no matter what the throttle opening (part-throttle or full-throttle).
Jetting
For baseline tuning, follow the recommended jetting from a Haynes Weber carburetor manual, or another Weber book.
I borrowed an excellent book from the library: Weber Carburetors Owners Workshop Manual by Haynes UK. Amazon.com link). It has this in the back. The B210 specs should be a good starting point for a stock A14.
Conversion equipment jet setting Datsun B110 (A12) - single 40 DCOE 2Datsun B210 & F10 (A14) - single 40 DCOE 2
Choke size 27 Aux. venturi 4-5 Main jet 1-10 Emulsion tube F7 Air corrector jet 1-65 Idle jet 0-50 F9 Accel. pump jet 0-50 Accel. pump inlet valve with ex. orifice 0-50 Needle valve 2-00 Datsun 510 (L16) - single 45 DCOE 13
Choke size 33 Aux. venturi 4-5 Main jet 1-30 Emulsion tube F11 Air corrector jet 1-80 Idle jet 0-50 F8 Accel. pump jet 0-60 Accel. pump inlet valve with ex. orifice closed Needle valve 2-00 Datsun 510 (L16) - dual 45 DCOE 12
Choke size 33 Aux. venturi 4-5 Main jet 1-30 Emulsion tube F16 Air corrector jet 1-90 Idle jet 0-50 F8 Accel. pump jet 0-50 Accel. pump inlet valve with ex. orifice 0-55 Needle valve 2-25
Choke size 32 Aux. venturi 4-5 Main jet 1-35 Emulsion tube F15 Air corrector jet 1-70 Idle jet 0-55 F2 Accel. pump jet 0-40 Accel. pump inlet valve with ex. orifice 0-55 Needle valve 2-00u
Also see discussion Help????? tunning Weber 40 DCOE on a14
40 DCOE-151 redline #19550.174 baseline jetting 32 Venturis 4.5 Aux venturis 115 Main jets F11 emulsion tubes 200 Air correction jets 45F9 Idle tubes 40 Pump jet 50 Pump exh 1.75 Needle valve
huicho: SINGLE 40 DCOE ON A STOCK A15 ROUND PORT COMPLETELY STOCK A15 economy version(round port head) Main Venturi 32 Aux. Venturi 4-5 Main Jet 140 Emulsion Tube F-11 Air Corrector Jet 200 Accel. Pump Jet 60 Accel.Pump Inlet Valve with Ex. Orifice closed Needle Valve 200 Idle Jet 55F9. If you do not use an air filter: * 180 on the air correctors * 130 on the main jets
Process
Start with venturi/choke size. For dual-carbs (one barrel per engine cylinder) 28mm is good for max power with good flexibility at 6000 RPM with a 1.2-liter engine. Larger venturis will make good power, but with less flexibility (flat spots, poor part-throttle response). See Carburetor Sizing.
Next, set the float. Everything is affected by the float level, so do this first.
Float Settings Early brass float: 8 to 8.5mm Late plastic float: 12.5 to 13mm
In DCOE series, the main jet should start at 4 x venturi size. For example, with 30mm venturis start with 120 Main Jets.
The Air Correction Jet should be 1.25 to 1.50 of the Main Jets (some say main jet + 50). For 120 main jet, start with 165 Air Jets.
That much is easy (setting the air/fuel ratio which is around 13:1 for all engines). The trickier part, for which tuning to the particular engine is called for, is the transitions:
- When accelerating the pump jet and duration are the main factors
- Transition between idle circuit and cruise circuit is controlled by the Emulsion Tubes and Idle Jets. Do not attempt to fudge this by raising or lowering the float level. The Float Level should be set to the Weber specifications before any other tuning is done.
Warm the engine up fully and set the Idle Speed. For a stock factory spec engine, set the idle speed to 800 RPM. The speed screw should be 1/4 to 1/2 turn in after contact with lever maximum. If it won't idle down to 800 RPM something is wrong - most likely the throttle shaft nut has been overtightened binding the throttle. But it could also be the linkage is jamming (inspect carefully). An air leak can also cause a high idle (either loose carburetor parts, a bad gasket, or a leaking/cracked hose).
After setting the idle speed, adjust the idle mixture screw to Lean Best Idle.
- If setting Lean Best Idle requires the mixture screw to be turned out 1-1/2 turns or more, the idle jet is too lean. Replace Idle Jets with half-size larger.
- If the mixture screw is 1/2 turn out (or less) from seated the Idle Jets are too rich. Replace Idle Jets with half-size smaller.
- If the Speed Screw is out more than 1/2 turn, the idle system is lean. This will cause problems with tuning the carb, so fix it now by fitting larger Idle Jets.
See also: http://www.redlineweber.com/html/Tech/dcoe_adjustment_layout_typical_i.htm
Heat Shield
Carb heat plate
キャブ ヒート プレート
Parts
Also see Intake Manifold
Kit includes manifold, carburetor, gaskets and linkage
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Weber K110 A12 twin DCOE Pierce Manifolds $1200
Weber K625 A14 single DCOE
* Pierce Manifolds $575 * Alamo $548
Linkage
Linkage depends on the manifold you use.
Twin-Pull with cannon small-diameter rod
Weber Kit