Solex Swan song

[1QuickS]

I like the look of Solex carbs when they are finished so I share a photo of my last Solex project along with some thoughts on why they were such a problem for Porsche.



Solexes were the factory's choice for production engines but Webers were used on race engines. When Solexes became a re-occurring problem for maintaining tune Porsche had Webers already developed so Solexes were replaced with them beginning in February, 1966.

Issues the Solexes suffered:

• erratic throttle valve closure rendering poor idle performance (they would have benefited with positive, screw adjustable throttle stop screws and concentric throttle return springs)
• fuel floats that absorb fuel and sink which caused flooding issues (brass fuel floats would have solved this issue)
• throttle actuation lay-shaft was mounted in simple bearings which caused it to further hinder accurate throttle valve closing
• complicated fuel delivery system involving mechanical and electric fuel pumps (a simple flow control metering system to supply fuel to the carbs and a scavenge pump with a return to fuel tank system would make the spill tube design work well.)
• throttle shafts were supported by mostly Teflon bushings (only a portion of the shaft was actually supported by metallic bearings which lead to wear induced throttle shaft movement which degraded low speed idling performance.)
• In addition to the above, these were six individual carburetors with a confounding level of redundancy and complication.

This set has new floats of brass construction, a real PITA to make:

[NZVW]

Gorgeous PA,

In my opinion anything that looks as good as those, is / are allowed to have a few personality idiosyncrasies.

[bob joyce]

I can only say …. back around 1972 ish….. A shop in Novato Ca., The 9/14 Shop. (to bad I don't remember the guys name) totally went thru my 6 solex . I mounted them on my car and it was a breeze to adjust them, they ran perfectly for the time I owned the car. (a few years). back then mechanics would say "those are flower pots" … "get Weber's"... I loved them and with the air cleaners off it was like a beautiful site.

[NTW]

Paul, that looks like quite a bit of work to do the floats! I did a small batch of 3D printed nylon floats which seem to be performing well(none for sale). Enjoy your retirement!

[Frank Beck]

I am proud to own some of Paul’s Solex work.

It’s exquisite.

[1QuickS]

Who said retirement????? Just no more Solex projects.

Thank you Frank for your "over-the-top" compliment.

[BillJones]

There are a few ways to improve the performance of these carbs as they have to be used on Period F Appendix K Race cars.

Reducing the clearance in the throttle shaft bearings is helpful but does need close tolerance shafts and improved bearings to be used.

The shafts which operate the throttle actuating levers also need improving as the roll grooved tubes never align well and are difficult to adjust. by making a close tolerance end fitting from a good quality steel helps with this problem and the same idea can be applied to the transverse throttle shaft.

One common modification to these carbs has been to add an O ring seal to the throttle shaft and we have found that this tends to produce a variation in stiction which doesn't help.

On Race cars we use a pair of low pressure Pierberg electric pumps connected directly to the fuel rails and then scavenge the reservoir as Paul suggests.

The next problem can be due to the condition of the two check valves in the accelerator pump and high speed enrichment circuits.

The upper valve is easy to remove and has a glass ball which is easy to clean or replace. The lower valve uses a brass ball and is retained by a simple pin.

When carbs have been neglected or stood around they can suffer from corrosion and either the ball becomes damaged or the seat becomes pitted and then the valve doesn't close correctly.

It is a good idea to dress the seat and replace the brass ball.

On race cars we normally disable the high speed enrichment circuit and jet for the specific application, this is easy to do as we make a gasket without the relevant hole to feed the gallery.

We have recently remanufactured Jet Carriers as 'bent' ears on the original Mazak castings can cause seating problems. They are hard to straighten and tend to break. Our new parts are made from a 6000 Series Aluminium Alloy and satin anodised.

We have made the Jet Carrier so it can be fitted with a tuneable idle air corrector jet rather than the hole drilled in the side of the original part.

[1QuickS]

Yes, one of the irritations in servicing these is the brass check ball for the accelerator circuit as Bill mentioned. I service these by removing the retaining pin retaining the lower check ball (shear off internal & external bits of the pin & drive remaining portion into the gallery so it can fall out), resurfacing the seat using a spherical ended milling cutter, peening the seat with a ball bearing of the same size as the replacement check ball silver-soldered onto a steel rod, replacement of the brass ball with a type 316 stainless steel ball bearing, making and installing a new keeper pin and finally peening the exterior of the body where the pin is installed. Do this six times for a set of these where Webers you can simply buy & install replacement valves.

I have one last set of Solexes that I am working on that are not OEM and the throttle stop issue along with the imprecise & wear-prone turnbuckles and lay shafts will be replaced with more durable & highly controlled items as Bill mentioned. They currently have 43mm throttle valves, a Weber IDA progression circuit, bell-mouthed intake air horns, tuneable idle air correction jets like Bill has incorporated and the manifolds are taper bored to a 37mm exit diameter. They were to be one of three types of trick carbs (43mm Weber, Zenith & Solex) for my 911 which I sold about two years ago so these are orphans to me now. The Zeniths found a home already, they were called "Zebers" as they were more Weber-like than Zenith.

I do like the spill tube concept of these. It is too bad Porsche/Solex did not sort these irritations of the Solexes but the ease of service and lack of complications of the Webers has been a relief to these issues for decades.