The Choke Tube (K on the drawings on page 4 & 5)
The Main Jet (G on the drawings on page 4 & 5)
The Auxiliary Jet (g on the drawings on page 4 & 5)
The F type SOLEX comprises in addition an auxiliary mixture regulating screw (W on the drawings below) which is intended for refinement of the idling adjustment.
To dismount the choke tube (K on the drawings on pages 4 & 5) remove the outer bell in the case of horizontal carburettors and loosen the choke tube fixing screw placed at the upper part of the body in the FH carburettors and at the side in the case of the FV carburettors, when the choke tube itself can be easily withdrawn.
When remounting, note that the choke tube (K) numbers indicative of size and type are stamped on the atmospheric side in the case of the horizontal and at the bottom in the case of the vertical carburettors. To dismount the main jet (G) remove the jet cap (A) To dismount the auxiliary jet (g) unscrew it by the aid of a small spanner.
As regards the choke tube (K) the diameter of this part can generally be determined by the table of adjustments.
The slow running adjustment is carried out entirely regardless of the main jet setting and resolves itself into two operations:-
1) MIXTURE ADJUSTMENT Try, to commence with, one of the jets indicated in the adjustment table on Page 20 selecting same as per the size of the engine.
TOO RICH A MIXTURE
Is recognised :-
a) By a rhythmic hunt or surge which the engine develops when warm. b) When the motor stops after having been idling some time in this way and the throttle is opened, a certain amount of petrol drops from the carburettor.
c) The plug points will generally be found covered with a coating of soot. In such a case chose a jet one size SMALLER
Is, on the contrary recognised by an irregular misfire when idling and by difficulty in starting.
In such a case one uses a LARGER auxiliary jet.
It is generally desirable to have the auxiliary as large as possible consistent with the avoidance of hunting when idling.
2) ADJUSTMENT OF THE IDLING SPEED.
Having determined the adjustment from a mixture strength point of view, the next requirement is the adjustment of the idling speed. To do this the slow running screw on the abutment plate is reduced until the required minimum speed is obtained.
The carburettors type F are provided in addition with an Air Regulating Screw (W on drawings above) for refinement of the auxiliary mixture. On rotating this screw outwards a slight air leakage is produced which reduces the strength of the mixture and vice-versa. By careful regulation therefore extreme correctness of mixture strength can be obtained easily.
It is best to commence by having it screwed fully home which will give the greatest richness and then gradually unscrewing it until the best performance is obtained. At the same time the slow running screw on the abutment plate can be reduced and by means of a suitable co-operation between these two members a perfect tickover will be obtained, the air regulating screw W being automatically locked in position by the spring.
It is well to make this adjustment when the engine is only moderately warm, for otherwise when cold the mixture will be found to be too weak and starting very difficult.