S3 E-Type

Balancing Quad Carburettors
An interesting method using Dial Gauges

by Dave Lacey

I've tried using both the 'hiss method' where you stick rubber hose in each ear and compare the intake hiss of each carburettor and the flow gauge method where you either buy multiple gauges or run between carbs trying to get them all the same.

Here's an interesting method using Dial Gauge/Indicators to measure the piston height inside the carburettor.

I learnt about this method the the "Rolls Royce Shadow Owners Companion", I'd never seen this before but it makes sense: The dashpot is there to sense the airflow thru the carb (by rising & falling) and thereby adjust the effective jet size (with the needle). So, why not just measure the position of the dashpot to know what the airflow is?


Here's my dial gauge with the adpators made by a local engineering shop.


The brass collar screws into the top of the carb where the plastic damper cap usually goes, the collar clamps onto the Dial Gauge itself.


In order to 'sense' the position of the dashpot, i needed an 'extension piece' for the nose of the dial gauge so that it rests on top of the oil damper tube. You can see how it fits in the pic below.


The drawings for the parts are available here:
1) The "collar" for the carb body
2) the "nosepiece" for the dial indicator

I used Mitotoyu indicators, of the "S Series" type 2045, 0.01 mm resolution, see here in middle of page.
Balancing Quad Carburettorssin|11 Dec : 17:41

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This is an interesting approach!

I got another idea that I am planning to try soon. I will misuse a low-cost DC-operated cooling fan in reverse mode together with a low cost digital multimeter. I will purchase the right diameter cooling fan and glue a suitable "O" ring to it to have a tight fit to the carburetor inlet. I will connect the DC-motor - now a DC-generator to the multimeter in the 20 VDC measurement set-up. Equal flows in individual carburetors should produce equal voltage readings. I will report my findings in a couple of weeks.

Please comment!


Re: Balancing Quad CarburettorsAdministrator |12 Dec : 19:46
Comments: 13

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Hi Sin,

I like it! Sounds like a modern approach to give a quantitative measure of airflow. Let us know if it works & show us a few pictures!


Re: Balancing Quad CarburettorsBill|19 Dec : 12:33

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Good idea, i'm going to try that. I'm tone deaf and can't tell the difference from carby to carby. I have severay cooling fans off PC CPU's. You could simply attach them to a piece of wood with a 2 inch hole cut in it, some thin rubber gasket on the carby side and just press it up aginst the carby to take your voltage measurement. To easy

Balancing Quad Carburettorssin|04 Mar : 06:42

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Hello E-Type Friends,

I finally built the proof-of-concept prototype. I used a used plastic juice bottle, a DC-operated fan from a discarded faulty PC power supply, a plastic fresh cheese box, general purpose glue, rubber band, and an inexpensive digital multimeter. I turns out that this really works. With the help of my vacuum cleaner I was able to observe that with low fan RPM the voltage generated was around 200 mV DC while with full speed from the 1500 W vacuum cleaner air flow I got 1800 mV DC. This seems promising. My next task is to get rid of the measurement fluctuations which I think can be tamed with a suitable capacitor across the multimeter contacts. I'll try to find a little time to remove the air cleaners of my Primrose Yellow S III OTS to do the real test. I'll also take a few photos of the black and yellow "instrument" for your reference. I might even include a picture of the car. Please give me a few days...


Re: Balancing Quad CarburettorsAdministrator |04 Mar : 10:00
Comments: 13

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Sounds a great gadget! Suggest you get some pics together and post at www.jag-lovers.org, hiliting the possibility to teh V12 list there!

Re: Balancing Quad Carburettorssin|04 Mar : 19:13

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Please give me the email address and I'll email a few photos,


Balancing Quad Carburettorssin|04 Mar : 19:00

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Here are a few photos of my proof-of- concept prototype. Image: d:\BlackHorn\IMG_5416.JPG
General construction
Image: d:\BlackHorn\IMG_5420.JPG
Interface to carburetor air inlet
Image: d:\BlackHorn\IMG_5424.JPG
DC operated fan used as DC generator
Image: d:\BlackHorn\IMG_5429.JPG
Measurement with full air flow from vacuum cleaner
Image: d:\BlackHorn\IMG_5431.JPG
Measurement with reduced air flow


Re: Balancing Quad Carburettorssin|04 Mar : 19:15

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Please advice how to attach photos. My first approach failed...

Re: Balancing Quad CarburettorsAdministrator |05 Mar : 12:06
Comments: 13

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try dave at xketype dot com

Balancing Quad CarburettorsGasman59|29 Oct : 20:40

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I've long thought that it would have been wonderful if ZS, or SU, for that matter had included a flow balancing "Tap" into the carburettor. basically a vacuum pipe to the front of the carb.
Now we could just attach standard ball flow meter to this tap and adjust the butterfly.
When done install a rubber plug and be done.
I have heard a few motorcycles have this design.

Balancing Quad CarburettorsSomeGuy_sg|10 Oct : 01:06

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Mm....there is actually an airflow meter you can use for balancing out the carbs. It was shown on "a car is reborn - e type jaguar"


Not to expensive :P

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