Thursday, 25 June 2015

Ferrari 400 Weber Carburettor synchronistation / tuning

Last week I was approached by someone for advise on tuning the carbs. My knowhow on this topic is very limited and I'm lucky to know a helpful and knowledgeable mechanic. Thought it might be useful to share his response. Furhtermore I obtained an additional document describing a similar process. I will add this doc in the download folder in the manual section. Note the same folder does have the Weber service manual as well.

Concerning the carburettor adjustments. You don't really need specific Ferrari information, setting up carburettors is pretty much the same on a Lada as on a Ferrari except you have a bit more carburettors on your car to work with.
First of all unattach the linking mechanism connecting all carburettors.
The best way to synchronize  is to attach 6 or 12 vacuum gauges to the intake manifold if you have vacuum tubes on your engine to attach something to. I think you have them, if you look at your carburettors, somewhere on the intake manifold close to where your carburettors are attached to the manifold. I guess they are interconnected to each other with some small rubber hoses.
Next thing, you could use a flowmeter to balance the individual throats of each carburettor. There is a small screw on your carburettor to synchronize the flow between each throat of the individual carburettor. This screw is really only for synchronizing 1 throat compared to the other troat of 1 individual carburettor. Screw them both in (gently) and screw one out until they are equal. Do this at all carburettors.
After that look at your vacuum gauges and screw the idle screws on you carburettors in or out until all carburettors are somewhat equal. Now they should be balanced.

Double check with your flowmeter if all carburettors are also somewhat equal on airflow and if neccesary make minor adjustments also trying to keep your vacuum as synchronized as possible at the same time.
Now attach the linking mechanism again and check if everything is still synchronized. If not make adjustments to the linking mechanism.
As the last step, apply some throttle so that the engine is running around 2 or 2500RPM and dubbelcheck airflow and vacuum again.

You really need quite some stuf to do it right, 6 vacuum gauges and at least 1 flowmeter.

If everything is balanced it's best to buy a glass colortune spark plug. Remove a spark plug, install the colortune, fire up your car and turn the air/fuel mixture screw until the color of the combustion is nice and blue. Do this at all cilinders.
Worst thing of it all is that if you have done your air fuel setting it will run more RPM and you have to repeat the synchronization steps again.

 UPDATE (6-7-2015): I received this additional information from another mechanic:

The manifold is equipped with a removeable nut per cylinder (thus per carb) as such you can realtime perform an exhaust gas test per cylinder and as such check if the burning indeed does correspond between them.

I wrote a small blog about this as well with a supporting video:
A while back I also have been in touch with someone who build a digital tool to tune up the carbs.
Its also listed on my blog:

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