With the engine running at working temperature, hook your finger under the pin and raise the piston about 1/32in. (1 mm). If, while the piston is raised, the engine speed increases briefly then returns to normal, the mixture is correct. If it rises and stays high, the mixture is too rich.
How do you set up twin carbs?
Let the engine warm up and set the ignition timing. Then, on each carb, wind the idle mixture screw in until the engine starts to slow down, then wind it slowly back out until it starts to speed up again. Leave it there. Adjust the idle speed screws the same amount on each carb until the idle speed is right.
How do you tune a single SU carb?
With the engine running at working temperature, hook your finger under the pin and raise the piston about 1/32in. (1 mm) . If, while the piston is raised, the engine speed increases briefly then returns to normal, the mixture is correct. If it rises and stays high, the mixture is too rich.
How do you adjust a Datsun SU carb?
- Remove the air cleaner. ...
- Warm the engine up to its normal operating temperature, then switch it off.
- Disconnect the choke cables.
- For both carburetors, locate its throttle adjustment screw. ...
- Find the fast idle throttle adjustment screw located on the linkage between the two carburetors.
How do you lean out SU carbs?
HS Type Carburetter: Tuning Single Carbs
(b) Turn the jet adjusting nut/screw (2) down/clockwise , to enrich or up/anti-clockwise to weaken, until the fastest speed is indicated; turn the nut/screw up/anti-clockwise until the engine speed just commences to fall.
How do I know if I have a SU carb?
The carburettor identification is made by letter prefix which indicates the float type: “H”: introduced in 1937 in which the float bowl has an arm cast into its base, which mounts to the bottom of the carburetor with a hollow bolt or banjo fitting. Fuel passes through the arm into the carburetor body.
Are SU carbs any good?
The SU is a good carburetor , fairly inexpensive, easy to tune unless they are warped, and easy to modify except for metering needles. I do not know the current supply of off-the-shelf metering needles. It used to be limited; and when we were still working on SU's, we made most of our own.
How do twin SU carbs work?
SU carburettors featured a variable venturi controlled by a piston . ... Since the needle is tapered, as it rises and falls it opens and closes the opening in the jet, regulating the passage of fuel, so the movement of the piston controls the amount of fuel delivered, depending on engine demand.
What oil goes in a SU carb?
The first is SU Damper Oil , which is a straight 20 grade and comes in a handy 125ml bottle. This oil is for use where the carburetter is fitted with a damper inside the piston and can be used on all SU, Zenith and CD carburetters.
How do you adjust twin Stromberg carbs?
Turn only an eighth of a turn at a time, then wait about 15 seconds for the engine speed to settle down. Lift the pin again and see whether the engine speed alters. Screw the jet upwards (that is, anti clockwise looking down on the carburettor) to weaken the mixture, or down (clockwise) to make it richer.
What does SU carb stand for?
The initials S.U. stand for Skinners Union . From these beginnings the S.U. Company grew into one of the major manufacturers of car fuel systems and components in Europe, its carburetters being widely used on both touring and competition vehicles. S.U.
How does a Stromberg carb work?
Fuel is metered by a tapered needle mounted in the bottom of the air valve , and a fixed jet. As the air valve rises, allowing more air to enter, the tapered needle also rises in the jet, allowing the proper amount of fuel to mix with the air.
How do you measure SU carb size?
The size is measured at the throttle/engine side .
Which carburetor do I have?
The list number is stamped on your carburetor, either on the corner of the airhorn or choke tower or, if it doesn't have an airhorn, on the mainbody. Remove the carburetor from your vehicle before looking for the list number to easily find the information you need.
