This month we are focussing upon the situation when the idling speed of a standard Series Land Rover petrol engine is inconsistent and may even stall on occasions.
Carburettor Float level problem?
Whatever carburettor is fitted to the engine, the float level for it could be set too low; this would result in fuel starvation. The procedure for adjusting the float level depends upon which carburettor is fitted and you need to consult the appropriate workshop manual for the full procedure and correct measurements..
Spitting back through the carburettor?
This may be the result of a very weak petrol/air mixture. You need to check for air leaks underneath the carburettor flange; often the result of over-tightening the alloy flange and twisting it. One way to diagnose this as the problem, is to carefully smear oil around the base of the flange and obseve whether it is sucked in whilst the engine is running. Care should be taken to keep oil off the hot exhaust manifold.
Zenith carburettor fitted?
Zenith carburettors may be fitted with tamper-proof idling screws; consisting of a screw and lock nut. These were fitted to Series Land Rovers sent to those export markets which had strict emissions laws. It is not legally permissable to tamper with these settings in an emissions control region.
To achieve the correct idling speed/mixture setting, carefully turn the volume/mixture control screw (situated just above the carburettor's base flange) inwards until it is just closed. Now unscrew it one and a half turns. Now rotate the throttle stop screw outwards until it just touches its stop, then turn it back in one full revolution.
Start the engine and leave it running until it has reached normal working temperature. Turn the volume/mixture screw again either in or out until the engine runs as fast and evenly as possible. Then adjust the throttle stop screw to achieve an idling speed of about 500rpm (this is about as slow as the engine will go whilst still running evenly).
If stalling is experienced on acceleration increase the idling speed. It should be noted that if an emission control system has been fitted then the idling speed will need to be set to 800rpm.
Solex carburettor fitted?
These were fitted to Series I,II and early Series IIA Land Rovers
This carburettor is sufficiently similar to the Zenith to be able to set the idling mixture using the same procedure as described for the Zenith.
SU carburettor fitted?
These were fitted to
some 2.6litre Series Land Rover engines.
In order to correctly set the idling speed, remove both the air hose and the damper from the top of the SU carburettor. Now hold down the central piston through the cylinder bore and unscrew the jet adjustment screw until you feel free play at the lever, then screw it back in one and a half turns. Run the engine until it's warm and adjust idling speed to 500rpm. With the damper removed, lift the air valve piston 1mm(0.03in) - this should not significantly affect the engine speed. Screwing the jet adjusting screw into the carburettor increases the mixture strength, screwing it out weakens it. If the emission control system is fitted then the idle speed needs to be set at 800rpm.
Stromberg carburettor fitted?
These are found on some 2.6litre Series Land Rover engines.
To adjust the idling speed, remove the air hose and the damper from the top of the carburettor. Inside the bore you will see an air valve piston - this should be held down whilst the central jet adjusting screw at the bottom of the carburettor is screwed upwards until it meets the underneath of the air valve. Next turn down the jet adjusting screw 3 turns. Run the engine until warmed up.Turn the throttle stop screw until the engine idles at 500rpm. With the damper removed, lifting the air valve piston about 1mm(0.03in) should not affect engine speed much at all. By screwing the jet adjusting screw into the carburettor you weaken the mixture, screwing it out enriches it. If the emission control system is fitted then the idle speed should to be set to 800rpm.
The Stromberg carburettor has a valve in the throttle butterfly disc that helps to control emissions on engine overrun. The spring in this valve can weaken in time and cause the valve to open too often, causing fast idling. The correct solution is to obtain a new butterfly disc, though some owners have been known to solder the valve closed if no local emissions law is contravened.
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