Hello
I have just fitted a pair of S.U. HIF's to my 3.5 and am about to start tuning them.Could somebody please tell me if you have to turn the mixture screw clockwise or anti-clockwise to richen them.
Many thanks
Graham.
Mixture screw?
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Hello Graham,
To richen the mixture on SU carburettors, turn the screw clockwise.
To get a ball park figure which is all we can do, unless using diagnostic equipment to measure CO, with the engine running, turn each screw out, ie anticlockwise until the engine revs start to drop. As soon as that happens, stop and then turn that screw one half turn back inwards to richen the mixture. Repeat with the other carb.
Don't worry too much about using the lift pins as a guide to mixture richenss. On the P6B, the idle mixture was originally set to 4% CO, but the engine will idle quite happily down around 2.5% CO, which is both good for using both less fuel and the environment.
N.B : The mixture screws are only used to adjust the idle mixture. The taper of the needle sets the mixture for off idle. Never touch the mixture screws when the engine is running above idle.
Idle speed is typically 650 to 750rpm. Using the idle adjustment screws and a vacuum gauge will allow you to set this.
Hope this helps,
Ron.
To richen the mixture on SU carburettors, turn the screw clockwise.
To get a ball park figure which is all we can do, unless using diagnostic equipment to measure CO, with the engine running, turn each screw out, ie anticlockwise until the engine revs start to drop. As soon as that happens, stop and then turn that screw one half turn back inwards to richen the mixture. Repeat with the other carb.
Don't worry too much about using the lift pins as a guide to mixture richenss. On the P6B, the idle mixture was originally set to 4% CO, but the engine will idle quite happily down around 2.5% CO, which is both good for using both less fuel and the environment.
N.B : The mixture screws are only used to adjust the idle mixture. The taper of the needle sets the mixture for off idle. Never touch the mixture screws when the engine is running above idle.
Idle speed is typically 650 to 750rpm. Using the idle adjustment screws and a vacuum gauge will allow you to set this.
Hope this helps,
Ron.
4.6 Rover 3500 P6B
