International Lancia Forums

Not sure what you mean by "drop". In waht situation? Is if momentary or all the time.

If it is the front carburetoor, it may be that it is not getting enough fuel. Possible causes I can think of immeduiately:

1. somewhere in the interconnectionn between the rear and the front carburetor there is dirt or a stoppage. In the connection (the brass union bolts) there are small brass filters. Check for any dirt
2. the float valve of the front carburettor itself contains dirt or is simply malfunctioning.

Sorry, I did not describe this too well. It turns out one of the accelerator pumps' check valves (with the ball) did not seat properly, meaning the pump circuit would slowly drain. Therefore, when getting back on the accelerator after, say coasting, there would be a slight hesitation as the circuit needs to fill before delivering the pump of fuel. Carbutettor shop cleaned up the seat and all is well now.

True, the ball+weight valve is an often overlooked problem. The seat (in Zamac) tends to corrode, making the valve no longer closing off properly. I got a special tool to recondition that seat. Most Fulvia carbs have a problem there, and it is often not recognized. I measure the condition of the valve with a special (home made) tool consisting of glass column filled with petrol fitted on top of the valve (about 10cc). Before reconditioning, it usually leaks through empty in a few minutes or even less. After reconditioning, it normally holds for at least 30 minutes (and then I call it a day, meaning I stop the test, as that is about perfect imho). Notice that some have seats that are so corroded that they are beyond reconditioning, and those need to be - sadly - rejected.