Balancing Dellorto DHLA Carburettors

Thanks to Richard Appley for permission to reproduce his original article 

Carburettor balance affects most aspects of your engines performance; throttle response, smoothness, fuel economy and running temperature. If you're running this type of setup (either Dellorto or Weber) then it is strongly recommended that you accurately balance the carbs, both barrel to barrel and carb to carb, before trying to optimise the jetting. You may find that a lot of "problems" just go away when the carbs are properly balanced.

Synchronising the carburettors consists of adjusting the flow of fuel-air mixture through each barrel so that it is exactly the same as each each of the others. The following balancing procedure assumes the carbs are in generally good condition, the floats are set to the correct levels (high and low limits) and the ignition is in good condition and properly timed.

Refer to the drawing and photograph, below, during the tuning procedure

Diagram of two Dellorto carburettors with various components labelled with numbers
Photo of a single Dellorto carburettor with various components labelled.

Key to diagram

Step by Step Procedure

Note - later cars have additional "F pipes" on the vacuum taps as part of an emissions controil system. (See also the vacuum hoses diagram) When these are removed, you will need to blank off the T-piece that they connect to. The easiest way to do this is to use a short piece of suitable hose to connect the two open ends of the T-piece together while you have gauges connected to the taps.

F pipes (home-made using windscreen washer T pieces)

Hose loop used to maintain vacuum while F pipes are disconnected.

Motorcycle vacuum gauges connected to carb. vacuum taps.

First start after rebuild

If you are starting the car for the first time since the carbs were re-built, the idle may not be anywhere close to right and you may need to complete a preliminary setup as shown below before you attempt to balance the carbs.