Rover service bulletin "Carburation"

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Rover service bulletin "Carburation"

Post by luli » Thu Aug 15, 2019 8:13 pm

Original Rover service department stencil.SERVICE BULLETIN.

(1940-1947 Models fitted with Solex FAI or FFIA carburetters with bi-starters)

In tuning, it must be remembered that engine condition is of greater importance than carburetter condition and this point cannot be too strongly emphasized, since even first class mechanics fail to obtain results because this vital fact is overlooked. For this reason we have divided the following instructions into two parts, (1) engine tuning and (2) carburetter adjustment, and the former should also always receive prior attention since carburetter adjustment is futile without assurance that the engine is in good tune.
A number of faults other than those concerning the carburetter will cause the engine to run badly and more often than not the trouble will be found amongst the following:-


To check this, crank the engine by hand and feel the compression on each cylinder in turn. If any cylinder feels weaker than the remainder, it must receive attention before satisfactory results can be obtained. Lack of compression may be due to badly adjusted tappets or to valves requiring attention.
In rare instances it may be due to a blown cylinder head gasket, thus allowing gas to escape from one cylinder to the one adjacent. In other instances it may be due to a loose cylinder head. The result will then be lack of copression on all cylinders and as water may find its way into the cylinders, traces of water are likely to be found on the plugs and in the oil. The existence of this condition can also be checked by noting if bubbles appear on the surface of the cooling water when the engine is running.


Plug points being set too far apart may cause misfiring and backfiring in the carburetter, especially on full throttle pulling hard on hills and when pulling light at approximately 30 m.p.h. The condition is also likely to cause difficult starting from cold. Clean, reset or renew plugs and reset gaps to .015 - .018 ins recommended for the model.


This condition will cause misfiring and the remedy is to dismantle and clean or renew as found necessary.


Tracking at the distributor or ignition leads will cause bad starting and misfiring. Clean and adjust the distributor points to between .010" and .012" gap and check free movement or contact breaker arm. Examine all ignition leads to plugs on both high and low tension leads to distributor for a breakdown in insulation and for a cracked distributor cap. Test the coil and check the condenser. The signs of a faulty condenser are, a weak irregular and yellow high tension spark with burnt contact points, the points usually also showing a yellow discolouration.


Sticking valves are likely to cause misfiring and back firing in the exhaust and through the carburetter. To check this point, remove the valve rocker cover and run the engine at tick over speed. If a valve is sticking badly it will set up a sharp metallic tap, as if the valve were badly out of adjustment. Hold firmly the push rod end of each valve rocker in turn. A distinct tap will be felt when the rocker corresponding with the sticking valve is held. Check the valve clearance to make sure that the tap is definitely due to a sticking valve and, if necessary, reset to .010" clearance with the engine hot.
If sticking valves are still suspected and will not show up on the above test take the car on the road when it will be found they will cause a noise similar to tappets out of adjustment at approximately 40 miles per hour with the engine hot and running under heavy load, at the same time the power will fall to a considerable extent. After a burst of high speed and on dropping back to low speed further indication of sticking valves is apparent in that the engine will not pick up properly. Sticking valves can be released by an application of upper cylinder lubricant into the valve guides. If the trouble ceases after such treatment it will tend to prove that the original diagnosis was correct and steps should be taken to decarbonise and free off the valves at the first opportunity.


Either of these conditions will cause the carburetter to give symptoms of a weak mixture, i.e., lack of power and popping back through the air intake. This can be tested by detaching the petrol pipe at the float lid to see if there is a free flow through the pipe and if air bubbles come through the pipe, an air lock is the trouble. This is usially caused by a shortage of petrol in the tank or by failing to change from main to reserve soon enough and can be cleared by priming with a hand primer if a mechanical pump is fitted or allowing the electric pump, if fitted, to operate with the forward end of the petrol pipe disconnected. Check the petrol filters in the electric pump if fitted and also in the carburetter.


A bad joint between the carburetters and manifolds and the manifolds and the engine block or worn valve stems and guides will cause bad starting and the engine will not idle. Check that the Luvax Bijur suction line is also satisfactory and no air leaks are present at this point.


A low engine running temperature will cause excessive petrol consumption and poor performance but as to whether artificial means of raising the engine temperature is necessary depends upon the conditions under which the car is being used. In winter weather, benefit will be obtained if the lower half of the radiator is fitted with a suitable baffle and on cars which are being used in cold weather for short runs only, a complete radiator muff is advantageous. Owing to the fact that a thermostat is fitted, this component should also be checked for satisfactory operation, otherwise, the condition may be aggravated.


Wherever circumstances permit, if a complaint of high petrol consumption is recieved, a road test of the car should be made before any adjustments are carried out and the actual consumption of petrol at a speed of 30-35 miles per hour should be noted with the aid of a consumption tank. This procedure is necessary in order when the final test is made to determine if any improvement has been obtained and to the exact extend. Whilst the test is in progress, the following points should be chocked.
a) For any signs of clutch slip.
b) For any signs of dragging brakes.
c) To ascertain whether the engine reaches a good working temperature.
If it is considered after test that the petrol consumption is excessive, check the engine as follows:-
1. For compression.
2. For clean plugs and correct ignition timing.
3. Adjust the carburetter to give a slow and even tick-over, making the setting as lean as possible consistent with even running.
4. Test again for consumption and ensure that this is undertaken under the same conditions as the original test.
5. If a general engine overhaul has been undertaken, check the valve timing to ensure that this is also correct.


In a great many instances this complaint will be coupled with high petrol consumption as they often originate from the same fault and consequently rectification procedure in either complaint is almost identical.
Road test the car and check the maximum speed and acceleration from 10-30 miles per hour in top gear against the figures given in the performance table. If the performance is below standard, proceed as follows:-
1. Check compression.
2. Check the plugs for misfiring by means of a neon plug tester. If misfiring exists but is only occasional, check as follows:-
a) Examine the contact breaker.
b) Check the ignition.
c) Check for sticking valves.
d) Check for a broken valve spring.

If misfiring is consistent check the following points in addition:-

a) Damaged cylinder head gasket.
b) Cylinder head loose.

3. Check that full throttle opening is obtained and whether fouling is taking place in the throttle linkage.
4. Ensure that the correct jets are fitted to the carburetter.
5. Ensure that the petrol supply is adequate and not obstructed.
6. Adjust the slow running.


This trouble may be due to (a) shortage of petrol, (b) sticking valves, (c) incorrect mixture, (d) late ingition timing and a check should be carried out as follows:-
d) Ensure that the jet sizes are correct.
e) Clean filters in pump and carburetter.
3. Check float chamber level.
4. Clean and adjust plugs.
5. Check and reset ignition timing as necessary.

SPECIAL NOTE: Lodge CB14 plugs should be used on the series concerned.

6. Check for air leaks between (a) the carburetter and manifold, (b) the manifold and cylinder block (c) at the Luvax Bijur air line, (d) worn inlet valve stems and/or guides.


` To carry out this test the car must be taken on a flat piece of road, an observer being required in addition to the driver for accurate timing, and preferably he should be supplied with an accurate stop watch.
Run the car in top gear at 5 miles per hour and depress the accelerator fully, as the speedometer needle comes up to 10 miles per hour mark, start the watch and allow the car to continue acceleration until 30 miles per hour is past, as the needle touches 30 miles per hour, the watch must be stopped. A reading should be taken in both directions over the same piece of raod and the mean of the time calculated.
Maximum speed on the speedometer should also be tested in two directions and a mean
of the two speeds taken. This test will require about two miles of flat out driving.


Model. M.P.H.
10 h.p. 10-30 in top gear, 15 secs, max speed 65-68 m.p.h.
12 h.p. 10-30 in top gear, 15 secs, max speed 67-70 m.p.h.
14 h.p. 10-30 in top gear, 13 secs, max speed 70 m.p.h.
16 h.p. 10-30 in top gear, 11 secs, max speed 70-75 m.p.h.
20 h.p. 10-30 in top gear, 10 sees, max speed 75 m.p.h.
The times and speed given above are to be expected with the driver only in the car and one second should be added to the acceleration figures for every passenger carried. It is assumed that the engine has been run in sufficiently and is fully flexible.


The correct valve clearance is .010" with the engine hot in both the inlet and exhaust and it cannot be stressed too strongly that it must be exactly .010" if the best results are to be obtained.


All adjustments to the idling and main mixture must be carried out when the engine is at normal working temperature.

SPECIAL NOTE: Under no circumstances must Jets be reamered. Jets are calibrated initially on pneumatic flow meters of great accuracy and if they become locked a fine spill of wood or other fibrous matter should be used to clear them.


The idling or pilot jet provides the necessary output for idling. The slow running screw mounted on the abutment plate of the throttle lever limits the closing of the throttle and thus fixes the idling speed of the engine. By screwing in this part the engine speed will rise and vice-versa.

The mixture adjustment screw permits the richness of the idling mixture to be varied. By turning it in an anti-clockwise direction, enrichment takes place up to the limit of the pilot jet output and conversely by clockwise rotation the mixture is weakened.
Poverty of mixture is recognised by the irregular behaviour of the engine and the tendency to stall. Over richness will cause the engine to hunt and tend to stall when the hunt becomes excessive.
In order to perfect the slow running, adjust first the screw on the abutment plate so as to fix approximately the speed of the engine and then experiment with the mixture adjusting screw until even running is obtained. As this operation will generally alter the speed, it will be seen that finally adjustment of both the Screw on the abutment plate and the mixture adjusting screw will determine the results.
Do not try and set the idling speed too low i.e., less than about 400 r.p.m. Slow tickover is not only difficult to obtain on modern high compression engines with light flywheels and flexible mountings, but it is an inadvisable practice as the cylinder bores depend for their lubrication on big end fling which is practically none existant below 400 r.p.m.


During cold weather when the engine has remainded at rest for a lengthy period it is advisable to give a few turns by hand to break the oil film before switching on the ignition and before pulling out the dash board knob of the Solex starting device.
After a long period of use, the following may occur; for the first few revolutions of the engine there may be no signs of starting and then a few late explosions and prolonged action of the starter motor will be required before normal firing takes place. This condition is occasioned by the inability of the pump to supply the required amount of petrol to the carburetter. It is as well therefore under such conditions to make use of the priming plunger, fitted to the pump where this is of the mechanical type, to fill the carburetter float chamber before attempting to start the engine.
Similarly, if the car has been standing for some time, say two or three days, the petrol in the float chamber may have evaporated or become somewhat stale, in consequence difficult starting may result during cold weather if the carburetter is not reprimed as above.

NOTE: The above only apply where a mechanical fuel pump is fitted.


The pilot jet, the main jet, and the starter air jet together with the starter petrol jet are all accessible from the exterior without dismantling the carburetter. Access to the interior is quite easy and obvious, the air cleaner should first be removed in the following way:-

Slotted square headed bolts will be found securing the top casting to the remainder of the carburetter, removal of these will allow the top to be removed, exposing the float chamber, air correction jet and pilot jet air bleed.

It will be seen that the float can be lifted out quite easily and only a small well fitting screwdriver is required to withdraw the two air jets, should it be necessary to remove them for cleaning.


The auxiliary carburetter forming the starting device is constituted to give the following benefits:-

c) A mixture which is richer proportionately as the temperature is lower
in order to ensure instantaneous starting from cold.
d) A means of weakening off the mixture rapidly by pushing in the dashboard
control half way as soon as the engine will take it, thus avoiding all
possibility of over richness, causing the engine to fade as engine
temperature rises.
,For absolute cold starting, the dash board control is pulled out fully and the main carburetter throttle should be allowed to remain in its normal idling position.
It is only necessary to pull out the control half way, i.e. to the bi-starter position when the engine is partially warm.
The Solex starting device has a secondary function, namely to assist the main carburetter when driving away immediately after starting the engine and should not be put out of action until the engine is sufficiently warm to function satisfactory on the main carburetter. This on later models is indicated by the appearance of the red warning light on the facia board.
Thus, there are three stages in the use of the starting device:-
f) Dashboard knob pulled fully out to start.
1. Dashboard knob pushed in half way as soon as possible this stage
is effected whilst driving away.
3« Dashboard knob pushed fully home when normal running temperature is reached.
Under no circumstances should the dashboard control be used when starting the engine when hot.


Year H.P. Type Main jet Correction jet Aux jet Air Bleed Starter air jet Starter petrol jet Choke tube.
1946-47 10 30FAI/S 115 190 40 1.5 4.5 110 22
1946-47 12 30FAI/S 115 170 45 1.5 4.5 115 23
1940-47 14 30FFIA/S 110 230 50 1.5 5 145 20
1940-47 16 30FFIA/S 105 230 50 1.5 5 145 21
1940 20 30 FFIA 115 230 50 1.5 5 145 23


When using the 30 PAAI carburetter instead of the FFIA on 6 cylinder models the following jet sizes should be adopted, Main 102.5, Pilot 60, Air bleed 1.5, Petrol jet 135, Air jet 5.0, Correction 240, Economy 55, Accelerator 55, Choke tube 22.


Apart from cleaning the carburetter occasionally, no attention should be needed for a considerable mileage. No moving parts contribute to the metering or correction of the main mixture, the only members which can wear with age being the needle valve and throttle spindle.
Be sure therefore, that the filter located inside the inlet banjo is periodically cleaned. If at any time you require to dismount the carburettors, see that the controls are put back in proper alignment so that no unnecessary stresses are imposed on throttle linkage, also ensure that soft and thick washers are never employed as flange joints as these will lead to air leakages and possible fractures through flange distortion.
It is as well to always approach fault diagnosis systematically and avoid doing more than one thing at a time for in that case it is impossible to ascertain from the eventual results which was the successful factor.


It is easy to see whether any of the exterior joints are loose, The first thing to do therefore when a carburetter floods is to check these various joints.


In the case of a carburetter provided with a filter, this usually only occurs within a few miles after fitting due to particles of oxide or packing material which are apt to get loose inside the petrol pipe-. Remove the needle valve and clean by carefully blowing out. Examine the valve to see if it is hermetic by testing with tongue suction whilst holding the valve on its seating by the fingers. If not airtight place on a flat metallic surface and tap it in by repeated and light blows rotating and testing periodically by suction until this is quite tight. Never grind in a needle valve as this will damage it irrepairably.


In such a case, one must either change the float or locate if possible the point of leakage and after emptying solder up as an emergency measure. Soldering will unbalance the float and a new one should be fitted as soon as possible.


Should it at any time be necessary to change an electric pump, be sure that the pressure does not exceed approximately 2 Ibs per sq. inch on 10 & 12 h.p. models and 2-1/2 Ibs per sq. inch on 14 & 16 h.p. models.


If, in spite of careful adjustment, regular slow running is not possible excessive induction leakage is almost certainly indicated, assuming the ignition to be in order. The condition may be cured by finding and rectifying air leaks at the induction manifold.


Banging in the silencer when over running down hill is seldom due to faulty carburation but more frequently to leaking exhaust joints or unsatisfactory sparking plugs.

Banging in the carburetter under load can be due to a weak mixture and if it does not disappear or tend to improve when the engine is hot, it is most probably an ignition fault. If it tends to get worse when hot, it is most likely due to an incandescent point in the combustion head, probably arising from a faulty sparking plug. If the trouble is accompanied by silencer banging under load, the trouble is certainly not faulty carburation.
Silencer bang under load can be only due to a live and fully combustible charge escaping unburnt from the cylinder. It can only escape unburnt if the ignition agency, i.e the spark was temporarily missing or if an exhaust valve is stuck open.
When reattaching the operating cable of the bi-starter, should its detachment have been necessary, hold the cable stop with a pair of pliers or other convenient tool whilst tightening up the screw, otherwise, the cable will be bent and stiffness will result.
Finally, it is as well occasionally to introduce a few drops of oil at the bends of the throttle spindle. If this is done when the engine is idling, it will be drawn into the bearing by the suctional effort of the induction and defer wear which otherwise may take place at this point.
Rover 10 1946 RHD
Rover 10 1947 LHD
Rover 12 1947 tourer LHD

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Re: Rover service bulletin "Carburation"

Post by GOY189 » Mon Aug 19, 2019 1:11 pm

Thanks for posting this Luli

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