Solex and Mikuni PHH Sidedraught Specialists

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How to rebuild the ADDHE Solex

Here is a picture essay on the ADDHE rebuild process courtesy of Sunray (Toyota3Tc Forum).  Sunray has graciously allowed me to up-load his forum report here for more to see and use.  It is reproduced as is (spelling and grammar into Australian English and links removed) and all permission to reproduce further is to be sort from Sunray.

I (Sunray) have noticed that there are a few people out there with these Solex c40 ADDHE carburetors.  They are the original predecessor to the Mikuni PHH except that these babies came out back in the 1950's!  They are not as refined as a Mikuni but they are tuneable.  I have seen lots of hoopla about how they don't work, etc, etc.  Combine that with the fact that there is almost nothing out there in English about these carbs and well.

I'll try my best to help here.


Many parts and procedures are the same as a PHH.  Also, be aware that there are different versions of this carb.  They feature different floats and emulsion tubes as examples.  There is lots of info out there on how to tune sidedrafts so I won't go off about that.  I also won't strip the carbs bare as most people don't need to.

C40 ADDHE dirty back-up version.

Some of the parts revealed and numbered:

#1 is the idle mixture screw
#2 is the idle speed set screw
#3 is the screw for balancing one carb to the other
#4 is just an access for balcing barrels on one carb
#5 is a accel pump jet
#6 is an idle air bypass screw for balancing the two barrels on 1 carb to each other.

This shows the jet cover removed.

Inside you find the pilot or idle air correctors (red arrow) which are pressed in.  This is a weak point of the design.  The Italians made the idle air correctors large enough so that most engines need large idle jets to reach a stoichiometric ratio.  To the sides of those are the pilot or idle jets, and the ones below are main air correctors.  Emulsion tubes are usually part of the air correctors and not changed by themselves. 
Note that unlike mikunis, the jet block is cast into the body.

Remove the 5 screws from the float cover to reveal the float bowl.  Some versions have the Mikuni style float attached to the lid, this one has it in the body.

When adjusting the float level, it is like some of the early Mikunis.  Spec. says 24mm up from the centreline of the throttle.  Or an easier method is to have it about where this little blanking plug is (red arrow).

This is the float needle block assy. Pretty straight forward to replace if needed.

This shot shows an air corrector with fixed emulsion tube on the left and an idle jet on the right.  All Solex jets are stamped with their number.  The number is metric in millimeters.  So a 140 is 1.40mm while a 54 is actually 0.54mm.

The starters which add fuel on cold start-up are identical to the Mikunis.

This little brass plug has an o-ring on it. It seals off the accelerator pump chamber allowing discharges out the accel pump jet (two accel pumps per carb).

Inside you find a check ball which sits in the bottom to stop fuel from flowing backwards and a spacer, then the block at the top.

The accel pump jet or nozzle actually sprays fuel into the airflow.

Unlike Mikunis, these ones spray across the air stream, instead of with the air stream.

The idle mixture screws.  Some versions can use an o-ring to seal the top from false air.  Ideally, they should be set around 1 and a half to 2 turns out and then set lean drop idle.

These bad boys are just plugs for attaching a vacuum tool to balance the two barrels of one carb to each other using the idle air bypass screws.

This is an idle air bypass screw.  They are usually dirty.  The o-rings are critical! turn both screws on a carb in just until they bottom.
 Then measure the vacuum from both of the balancing plugs above.  Leave the screw on the weakest vacuum barrel alone and unscrew the stronger barrel screw (higher vacuum) to bleed vacuum until they are matched.  This is an adjustment that many people who work with sidedrafts do not understand.  This is done BEFORE balancing one carb to the other.

Before I go any further, here is the original return spring location.  Each carb was originally equipped with one.

Now looking at the bottom of the carb.  I have numbered some parts but also notice these have a diaphragm accel pump. Very efficient just like a Mikuni!


To remove the pump, undo the four OUTER screws.  Then you can disassemble the pump.

Inside you find another ball under the plug.  This is a one way valve to allow the pump to push and not pull.

This bit I (Rodger) dislike on the Mikuni/Solex PHH as the ball is not under a plug and they can sometimes clog up and stick the ball closed rendering the pump housing next to useless.

Main fuel jets are located under the accel pump. This part I like better in the Mikuni.

On that last numbered picture I had you need to know the following:
#7 holds the outer sleeve
#8 holds the booster (Inner) venturi
#9 holds the Outer venturi (sometimes called a choke)

I like to remove all these at once. The parts are tight so I remove the outer sleeve and Inner Venturi at once by using a screwdriver and pushing the Venturi towards the inlet of the carb. The Venturi will push the sleeve out.

Separate the two. Sleeve on the left, Inner Venturi on the right.

Note that this Inner Venturi needs a new o-ring.

Now we can easily remove the Outer Venturi (choke).

Here is the sleeve, Inner Venturi/booster, and Outer Venturi/choke.

Most of the time, this is as far as you need to go.  If you have to strip it further then you likely are a person who wouldn't need this write-up anyway.

I hope this helps someone out there!

Thank you Sunray I hope it does help too.


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Updated 15/01/2022