This can be measured on a
flow meter placed across the intake of the carb, or by listening (via a
hose but practiced ears don’t need one) to the level of suck at the
intake. If using a hose, make sure it is held at the same point relative
to the intake of each carb. Any difference in noise level not
discernable by the ear is not worth worrying about.Chevrolet corteco oil seals.
Mixture adjustment on SU carburettors
Note: This must be done after balancing the flow, as there is transfer between the ports via the balance pipe in the manifold, and if the flow in the carbs is not about even, there will be a major effect on the opposite port when adjusting any given carb.
Adjustment mechanism
There are two means of adjusting the mixture on SU’s originally fitted to most MG’s, depending on carburettor type:
The H and HS type of carburettor fitted to prior to about 1972 have an adjusting nut underneath the carburettor, around the base of the jet.Chevrolet corteco oil seals.
The HIF carbuerttor fitted to MGB’s from about 1972 onwards adjustment is via a recessed screw in the side of the carb body, quite low down and at about 45 degrees to the main throat of the carburettor.
(Note that post 1972 Midgets retained the HS type, and that the change-over period was 1972-74 for the MGB so either type could be fitted to these years. The HIF does not have a separate bowl, instead it is underneat the carb, incorporated into the body.)Chevrolet corteco oil seals.
Checking mixture strength
Lift the piston about 1/16” (either via the piston lifter on the carb body, or with a screwdriver or other probe small enough to not disturb the air flow into the carb.) Correct mixture is when the engine speed doesn’t change or increases a little then settles back to where it was. If the engine speed reduces the mixture is lean, if it increases the mixture is rich.Chevrolet corteco oil seals.
This is the only reliable way to set the mixture, though you can get it roughly there by screwing the adjuster in and out till it maximises idle. However, it still pays to do the last bit by piston-lifting.
This entry was posted in Engine – Tuning, MGA-MGB, Midget. Bookmark the permalink.Chevrolet corteco oil seals.
Mixture adjustment on SU carburettors
Note: This must be done after balancing the flow, as there is transfer between the ports via the balance pipe in the manifold, and if the flow in the carbs is not about even, there will be a major effect on the opposite port when adjusting any given carb.
Adjustment mechanism
There are two means of adjusting the mixture on SU’s originally fitted to most MG’s, depending on carburettor type:
The H and HS type of carburettor fitted to prior to about 1972 have an adjusting nut underneath the carburettor, around the base of the jet.Chevrolet corteco oil seals.
The HIF carbuerttor fitted to MGB’s from about 1972 onwards adjustment is via a recessed screw in the side of the carb body, quite low down and at about 45 degrees to the main throat of the carburettor.
(Note that post 1972 Midgets retained the HS type, and that the change-over period was 1972-74 for the MGB so either type could be fitted to these years. The HIF does not have a separate bowl, instead it is underneat the carb, incorporated into the body.)Chevrolet corteco oil seals.
Checking mixture strength
Lift the piston about 1/16” (either via the piston lifter on the carb body, or with a screwdriver or other probe small enough to not disturb the air flow into the carb.) Correct mixture is when the engine speed doesn’t change or increases a little then settles back to where it was. If the engine speed reduces the mixture is lean, if it increases the mixture is rich.Chevrolet corteco oil seals.
This is the only reliable way to set the mixture, though you can get it roughly there by screwing the adjuster in and out till it maximises idle. However, it still pays to do the last bit by piston-lifting.
This entry was posted in Engine – Tuning, MGA-MGB, Midget. Bookmark the permalink.Chevrolet corteco oil seals.
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