Solex Carburetor Setting

Discussion of 4-Cam Type 547 engines (and all the Fuhrmann racing variants) and cars that powered them.
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Thomas Laubscher
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Solex Carburetor Setting

#1 Post by Thomas Laubscher » Sun Aug 15, 2021 11:59 am

Actually I'm doing the setup of my rebuilt 2 litre engine with Solex 40 PII-4 carburetors.
To do the proper setup I measured the lambda value (I think this is AFR in the States) during my testdrive on the road and I could see that the value is always 0.84 or less except on idle.
So I think I should maybe use other main jets? I have standard Carrera 2 configuration.
How do you do your setup? Do you work with a lamda sensor or do you just measure carbon dioxid?

Thanks for any advice
Tom

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David Jones
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Re: Solex Carburetor Setting

#2 Post by David Jones » Sun Aug 15, 2021 12:36 pm

I have never used an O2 sensor for tuning having in the past had a dynamometer and was always looking for peak torque. For a street car I have relied on seat of the pants and an IR gun to tune at idle with again seat of the pants and observation for acceleration and choice of idle jet. Rarely have I deviated very much from standard main jets unless I was obviously tuning out of fuel at high speed/load. Your O2 seems to indicate a rich condition from my reading so you may want to reduce size of either the idle or main jet depending on where you are in the rev range.
https://en.wikipedia.org/wiki/Air–fuel_ ... ometry.jpg
If I had known I would live this long I would have pushed the envelope a little harder.
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Bill Sargent
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Re: Solex Carburetor Setting

#3 Post by Bill Sargent » Mon Aug 16, 2021 12:21 am

Hi Thomas,

Assuming your motor is a stock Carrera 2 (587/1) with stock dot 1 intake and exhaust cams and stock valve timing the best place to start is with the factory recommended jetting for the Solex 40 PII-4. The values shown below are from the Springer/Heinrichs Carrera Book.

Main jet = 130
Idle fuel jet = 60
Idle air jet = 1.6
Venturi = 36 mm
Air correction jet = 180
Accelerator pump jet = 50
Accelerator pump volume with 2 strokes = 0.65cc summer, 0.85cc winter
Enrichment jet = 0.7
Float needle valve = 1.75
Emulsion tube = 25

These will likely have the motor running rich below about 4000 rpm, so if you spend too much time below 4000 rpm you may have plug fouling issues. A CD ignition will help with the plug fouling.
Regards,

Bill Sargent
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Alan Hall
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Re: Solex Carburetor Setting

#4 Post by Alan Hall » Mon Aug 16, 2021 11:40 am

A few years ago I was working on a writeup on all versions of carburetors used on 356 motors. Attached is the jetting chart for 4-cam versions of Solex 40-pii-4 carbs. The chart may not be complete as I never finalized the writeup.
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40pii-4(4cam)jetting.xls
(20 KiB) Downloaded 76 times

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Thomas Laubscher
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Re: Solex Carburetor Setting

#5 Post by Thomas Laubscher » Mon Aug 16, 2021 4:48 pm

Hi All

Thank you very much for your posts. I have a standard 587/1 engine with standard cams but modified pistons and higher compression. Currently I use smaller airfilters, not the big C2 filters. Do you think this has a bad impact?

I've standard C2 jets in use. I tried just upto 4000 RPM because the engine is in new condition. So up to this rev it is always too rich, above I've no clue at the moment.

Would you try to use a smaller main jet or leave it? I think the lambda value should be somewhere at 0.9.

Olivier AUVRAY
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Re: Solex Carburetor Setting

#6 Post by Olivier AUVRAY » Tue Aug 17, 2021 2:11 pm

Thomas Laubscher wrote:
Sun Aug 15, 2021 11:59 am
Actually I'm doing the setup of my rebuilt 2 litre engine with Solex 40 PII-4 carburetors.
To do the proper setup I measured the lambda value (I think this is AFR in the States) during my testdrive on the road and I could see that the value is always 0.84 or less except on idle.
So I think I should maybe use other main jets? I have standard Carrera 2 configuration.
How do you do your setup? Do you work with a lamda sensor or do you just measure carbon dioxid?

Thanks for any advice
Tom
0.85 lambda = 5% carbon monoxyde = best power output

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Greg Bryan
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Re: Solex Carburetor Setting

#7 Post by Greg Bryan » Tue Aug 17, 2021 2:25 pm

As usual, Olivier is right - see this chart from the interesting link that David posted.
Max power and enough fuel to provide extra cooling for the piston and cylinder head
Attachments
Lambda chart.PNG
Lambda chart.PNG (116.93 KiB) Viewed 1401 times
Greg Bryan

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Thomas Laubscher
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Re: Solex Carburetor Setting

#8 Post by Thomas Laubscher » Tue Aug 17, 2021 3:50 pm

Okay, that means if I go for an average lambda of about 0.85, it will be not wrong.
I was just wondering if someone else is adjusting the Carrera motor by measuring the lambda value or not.
In my case I'll try to reduce the main jet a little bit and measure again. Maybe it will come closer to 0.85.

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David Jones
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Re: Solex Carburetor Setting

#9 Post by David Jones » Tue Aug 17, 2021 5:11 pm

I think I would try smaller idle jets first.
If I had known I would live this long I would have pushed the envelope a little harder.
Cymru am byth
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Greg Bryan
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Re: Solex Carburetor Setting

#10 Post by Greg Bryan » Tue Aug 17, 2021 5:57 pm

I am using a O2 sensor and a matched A/F ratio gauge currently on my pushrod motor which I'm running Webers on - I used a 912 exhaust pipe 2 into 1 at the muffler outlet with the O2 sensor installed. I am very impressed with the virtually instantaneous feedback that it provides. To complicate matters, I am at 6300' elevation - it's currently running about 12-13/1 AFR during cruise with my setup - I was at sea level for a day with it and it was about only a half a unit leaner, much to my surprise. I know this is not useful for your original question regarding a 4-cam motor, but having the gauge sure takes the guesswork out of tuning carbs. I made it portable, so when I'm done with this car, I'll move it to the next. It was pretty cheap, too - about $200US for the O2 sensor, a bung, a well made harness and the AFR gauge and a comprehensive instruction sheet. You can add recorders and other equipment to the setup as well which I didn't opt for.
Greg Bryan

Jerry Powell
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Re: Solex Carburetor Setting

#11 Post by Jerry Powell » Wed Aug 18, 2021 8:03 am

Greg--Please post a link to purchase your $200 A/F ratio setup.

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Greg Bryan
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Re: Solex Carburetor Setting

#12 Post by Greg Bryan » Wed Aug 18, 2021 12:12 pm

https://www.amazon.com/gp/product/B0184 ... 58ca54e1d2

Bought it through Amazon (imagine that)
Came from an outfit called Highend Autosports
839 W. Covina Blvd
Covina CA 91722

I made it portable so I can use it on other cars once I get the carbs dialed in. I power it from a small agm motorcycle battery because my car is still 6V.

PS - I was told it's important to buy as a kit as the O2 sensor and gauge are matched.
Greg Bryan

Jerry Powell
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Re: Solex Carburetor Setting

#13 Post by Jerry Powell » Wed Aug 18, 2021 2:54 pm

Greg--Can you post a pic of the 2 in 1 exhaust pipe with the sensor installed.

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Greg Bryan
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Re: Solex Carburetor Setting

#14 Post by Greg Bryan » Wed Aug 18, 2021 3:12 pm

I don't have a picture and we have left the Tahoe basin - where the car is - because of severe smoke in the area from the fires elsewhere.
It is the standard 912 tailpipe interface - between the muffler outlet and the tailpipe. I had to remove the backup light to fit it in place, but since it's temporary, I'll put it back when I'm happy with the carb setup.
I had a muffler shop weld in the bung at the top so the O2 sensor sticks straight up. The muff shop also made a short tailpipe fitted to the 912 connector. It's all a tight fit but works. The 912 part is expensive, but I had a used one around that I used and will reuse.
912 tp.PNG
912 tp.PNG (461.89 KiB) Viewed 1338 times
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Jerry Powell
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Re: Solex Carburetor Setting

#15 Post by Jerry Powell » Wed Aug 18, 2021 6:15 pm

Thanks Greg,
That installation is too complicated for me, although I appreciate your effort. I think I can use the AEM gauge setup on my 83 911 with CIS induction and a cat bypass.
I would just install the AEM sensor next to the existing OX sensor.
Be safe.
Jerry

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