Monday 11 December 2023

Solex Idle Circuit

I've known for some time that I didn't have a drawing of the Solex 26 AHD on the blog. Today, coincidentally, someone was asking about the jet locations and problems with idling on the AOMCC Forum. I uploaded a drawing and Pete Silson provided some wise words, and an annotated the drawing to suit. Before we get to that, note that the fuel follows the orange highlighted path before it reaches the pilot air bleed jet, when the blue mixture path begins:

I don't believe the notch under the choke tube has any effect on tick-over. The four usual sites for blockage of the pilot mixture path are shown in the diagram below.


Air leaks anywhere in the mixture path (blue in diagram) cause erratic tickover. Blockage of the pilot jet (3) weakens the tickover mix, blockage of the pilot air bleed (4) richens the tickover mix. There are two small holes either side of the butterfly (1 & 2) which can also get gummed up - the size of these are important so best to blow them through with air rather than poking with wire.

The tickover mixture is governed by the ratio of the Pilot Jet 070 (0.7mm) and Pilot Air Bleed 150 (1.5mm). The tickover mixture is further adjustable using the Volume Control Screw - clockwise for weaker, anti-clockwise for richer. The tickover speed is adjusted by the throttle stop on the main butterfly.

The ratio of the Air Correction Jet and the Main Jet and the Emulsion Tube controls the mixture over the whole rev range. The Air Correction Jet has more influence at higher revs.

The jets are illustrated in this post. Apparently Mikuni were agents for Solex at one time and Mikuni jets fit these carburetters.

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