Having just replaced the full fuel system on my 1976 Fulvia 1.3 S3, (new tank, carb overhauls, fuel filters pipes & hose), I found that the easiest way to balance the carbs was to use a syncronometer. This is nothing more than an airflow meter designed to seal on each individual trumpet.
Having had the carbs rebuilt by Gower & Lee, they were set up as per the manual, mixture screws screwed in fully (very gently though) & then backed off one quarter turn. Balance set by eye. The engine was then started and the syncronometer used to measure the airflow to each barrel. Surprisingly, as they looked to be perfectly balanced, the rear pair showed a flow of 10 & the fronts 3. Adjusting the balance soon had them both sitting a 10 (not sure what the divisions are!) & the engine running quite smoothly.
After that, the mixture screws were screwed out & the engine speed increases. When the increase stopped, the idle speed was slowed to normal & the next screw adjusted. Once all 4 were done, a couple of test runs of about 6 miles over differing terrain for minor adjustments & she seems to be running as sweet as a nut.
