Solex 40PI service

[1QuickS]

I just completed a Level 3 remanufacturing effort on a set of Solex 40PI carburetors and wanted to share a few things I learned:

• The throttle shaft wear experienced during low mileage was due mostly to a poorly supported throttle shaft. The shaft was installed in the throttle body and only the aluminum of the throttle body was the bearing support. Since the aluminum easily deformed under closed throttle pulsations it is no wonder that they leaked so soon. I installed oil-filled bronze bushings for the length of each throttle shaft bore, resized the 40mm bores to clean up the ends of the bushings and fitted new butterflies.
• The accelerator pump assembly in each throttle body is a vertically stacked system with the top ball valve assembly pressed into the top of the fuel gallery. The lower ball valve consisted of a ball that seals with a seat that is machined into the throttle body. This makes repair of a leaking valve difficult, especially when access to the lower seat is blocked by a 1.5mm brass cross-pin that must be extracted first.
• The throttle shaft height from the intake of the head for the Solex carbs falls halfway between that of OEM Weber and that of the Weber sitting on a tall intake manifold.
• The auxiliary venturis are similar to those used in the Zeniths in that they are both somewhat taller than the OEM Webers and neither have the main fuel nozzle protruding into the air stream like the Webers do.
• The throttle actuating bars were yellow chromated while the hardware on the throttle bodies were left as silver zinc plate

When I test ran the carbs I used a fuel delivery system other than the OEM design. I ran fuel through a pressure regulator set at 3 1/2 psi and then through an adjustable flow control valve. The fuel lines were split with each one attached to the inlet fuel lines running to the banjo fittings. Fuel was collected from the bottom of the fuel bowls on the manifolds (floats were removed) and then sent back to tank. This is a system racers have adopted to overcome some of the issues with the twin Pierburg pumps. The holes in the banjo bolts had already been enlarged to 1.2mm which was one of the early factory recommendations for these carbs.

I sent the fuel pumps to Ed Fall of Vintage Werks (an ESR advertiser) and was extremely satisfied with his personal attention to my particular project, highly recommended!

I attach a couple of pictures; the manifolds and some of the unfinished bracketry are mine and not correctly finished but the throttle bodies are per OEM. The accelerator pump jet components are displayed in their correct orientation, the throttle shaft is shown correctly configured in relation to the throttle body showing the aluminum portions for shaft support just outside of the throttle valve followed by nylon bushings and a very short bronze bearing.

[Fritter]

Interesting stuff Paul. You would think that Porsche should have known better on some of the design features on the Solex's. And I think the triple barrel Webers were already out when the Solex's were designed, so maybe Porsche could have learned a few things from them before releasing the Solex's. Might be an example of listening to a trusted old vendor a bit too much!

A fully functioning set of these babies on a '65 or early '66 is definitely the cherry on top of the sundae. Cool factor is definitely a 10.

[John Straub]

Paul,

Great info!

John

[Joe901]

I don't quite understand the third photograph.

If I understand correctly the 'ball' on the left is the ball valve which is presented from rising by the brass pin, which is the item next to the ball.

Is the 'tube' the brass part that is pressed into the body of the carb?

I can't quite see how the upper ball valve is installed in this tube do you have more information?

All very interesting and useful.

[1QuickS]

Joe901,

Your understanding is correct; the first ball is brass and is retained in the bore of the throttle body by the brass cross-pin. The glass ball is part of a three piece assembly; a lower sleeve with the seat, the glass ball and the upper tube which has its lower end inserted with a light press-fit into the ID of the lower sleeve. I didn't know about the light press-fit assembly until I took a closer look thanks to your question.

[Joe901]

Paul,

Thanks, very useful and interesting.

If the carbs 'rattle' indicating the balls are free do you think that there is a need to remove these parts and reface the seats?

I imagine that it wouldn't be too difficult to replace the brass parts with new components and to 'peen' the lower seat with a suitable drift.

I wonder if it would be possible to replace the brass ball with Stainless Steel as the density is only about 6% lower.

I think window and bottle glasses have a specific gravity of about 2.5 and it should be reasonably easy to find replacements that are made to a high degree of precision. I would imagine that there are some ceramics with a similar density.

[Joe901]

I have now had chance to look at the 'upper' brass insert as shown in your photo and they appear to have a small diameter thread on the ID and I plan to try to make a small puller to see if I can remove them without drilling.

Unfortunately I don't have a 'macro' capability on my camera so I can't take a photo to show this.

[1QuickS]

I made a puller to draw out the brass insert as you suggest, the brass cross pin is another issue... I remove these pins if warranted and then re-cut, peen and lap the lower seat before replacing the brass ball with a stainless one. I haven't had an issue with the glass balls (I suspect Pyrex or some other material; ceramic as you suggest would be a good substitution) which is due to the lack of galvanic corrosion potential like there is between the brass and aluminum for the lower valve. Also, the upper valve is above the fuel level so many corrosion issues are mitigated by its drying out when the engine is shut down. The lower pin may be drawn out but it is easy to break the tip off leaving you with the issue of centering on the pin axis and drilling it out. In either scenario you will need to replace the pin in such a fashion to seal the throttle body to the OD of the pin to prevent fuel leakage. The original pin installation was peened with an annular drift to "clinch" the pin into the outer wall; have a close look at the throttle body around the pin to see what I mean.

Best to check squirt efficiency BEFORE "diving-in" on this repair.

[edmayo]

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I think you're a little off topic here!!

[Joe901]

I have looked carefully at this area of the carb bodies and I agree that it is best to pull out the pin.

I think the pin is probably tapered and was originally from a watchmakers kit. I think it maybe easier to seal with a taper than by staking.

The pin could be knocked in with a simple tool and I think it is this that makes the witness.

I have just ordered a box (120) of 8.5mm long tapered brass pins form a specialist Clock Components supplier in Birmingham's (UK) Jewellery Quarter where they still make this type of part.

The price was not too high and when we have installed one I will try to pressure test to make sure it doesn't leak.

Thanks again for the help.