Solex 40 PII adjustment dilemna

[Roland Paetsch]

.....and I have a table showing that the 912 616/39 EECS Solex has main jet 122.5 and idle jet G55. So maybe it is just a matter of fine tuning the carb to meet the emission regulations. Afaik the 06 is for the 69 912, I don't know about the 05.

Regards,

[Dave Erickson]

I did a bit more inspecting of 40PII's, starting with solid shaft carbs in the 3000 serial number range, up to split shaft carbs in revs 05 & 06, as well as some that came as replacement carbs in later years (with 4 digit serial numbers). I have about (80) 40PII throttle bodies, so I looked at quite a few.

All of the solid shaft bodies were machined the same (even those below 6000 serial number), and had independent idling and main jet circuits: each circuit has its own fuel supply.

All of the split shaft bodies were machined the same and had dependent idling and main jet circuits (the idle circuit is fed on the outlet side of the main jet).

So it is no wonder that the jetting changed with the introduction of the split shaft, and it also makes sense that if you change the main jet on a split shaft carb, you may need to change the idle jet as well and/or the idle air jet.

I could not find any support for the claims I have read that solid shaft carbs below 6000 had dependent idle circuits and don't work as well, or that the latest split shafts were different in some way from the earlier ones (other than jetting).

-Dave

[Mark Sabbann]

Important points...

4-after the jetting is correct-accel pumps are adjusted to get the best tip-in response-the accel pumps do nothing during steady throttle and have only a short duration affect as the throttle is pushed to the floor-get nyloc nuts at the hardware store to replace the jam nuts-use a little aluminum spark plug end, drilled to slide over the shaft as a spacer-set the pumps even and within spec-drive the car, possibly over a period of weeks-carry a wrench and turn each nyloc a turn at a time until you find the correct setting wether that be leaner or richer than spec

I am reviving this thread to keep my question in context.

Cliff's method for an easy way to adjust the accelerator pump output makes a lot of sense, but for clarification, does moving the nut down the pump shaft and exposing more threads, lengthen the stroke (more fuel) or shorten the stroke (less fuel)?

[C J Murray]

The nut screwed further onto the shaft increases the volume of fuel.

[Mark Sabbann]

Thanks Cliff, That's what I deduced, but I couldn't find info that clearly defined that relationship.

[Mike Horton]

There are two factory jetting configurations for the 912 Split Shafts, an early, 616-39, and a later version, likely the 616-40, as found in the late 900 Little Spec book, as well as the difference Cliff mentioned, in the two exhaust configurations, for the early 616-36 solid shaft version, most equipped with the dry paper air filters. In the 356 Little Spec book, the solid shaft carbs shown for the S90, and SC, show different jets, and much smaller mains, but...with the "oil-wetted", rock catcher filters,... ah, another difference. I've also found, that the Euro 616-39, & -40, had the 57.5 idle fuel jets, where the U.S. smog calibrated units, had the 55 idle fuel jets, likely to meet the then new tailpipe sniff tests. So as in all things Porsche, simple, right?

As an old 6'5" (real) Cowboy engineer I once worked with in Amarillo's Bell Helicopter Military Assembly Center always said, ..."only a 97 simple step solution"... it all matters,

[Paul Lima]

I read CJ Murray's suggestion above in this thread for making the accelerator pumps adjustment on the Solex 40PII easier and embarked to change my carbs. First discovery: the actuator rod thread is M4x0.75 and nobody carries this size since the DIN standard coarse thread is M4x0.7 A friend suggested re-tapping the nyloc 0.7 with a 0.75 tap and this worked(??!). Then I found that the spark plug nut that we all throw away would have only a 0.010" wall left if I drilled them to slide over the rod, so I ordered brass tubing to fit. It is still a brilliant solution but not as simple as I'd thought!

[C J Murray]

Hi Paul. It's been awhile since I have done that but it was pretty easy as I remember. I found the nyloc nut at my local hardware store. I did have to drill out the spark plug top but it still left enough material. I don't know.

[David Green]

The Registry's new Technical and Restoration Guide, Volume 2, has a great tip on checking float levels with the engine running by inserting a calibrated hypodermic needle into the air correction jet to measured depth and seeing in you can suck up any fuel. It's a reprint of an article by Giacchino Stagni, Volume 23-4. I'm running original Solex 32 PBJs on my '53 1500 55 hp and the needle technique compares closely to the actual float bowl levels.
David

[Paul Lima]

Hi Cliff, I just completed the change over; this is a brilliant modification, making it easy to try different accelerator pump settings. Thanks!

[C J Murray]

Hi Cliff, I just completed the change over; this is a brilliant modification, making it easy to try different accelerator pump settings. Thanks!

Glad to hear it! I've never been called brilliant before. You made my day!

Hey Sebastian, hear that, I'm "brilliant". Would you like to change your assessment? I'm just kidding!