We have a Catalina
27 with the A-4, but no tachometer.
Normally we cruse about 5.25 or 5.5 knots and burn around 1/2 gallon per hour. At hull speed
we burn about 0.75 gph and in bad weather
& rough seas we can burn in excess of 1 gallon per hour. These numbers have held up over the last 400 hours of engine
We usually cruise
at the slower speed to extent our range (10% speed reduction gives us 50% more range).
For better starting and lower gas consumption
I suggest you adjust the carb carefully to run as lean as possible, this will also help prevent carbon fouling on the plugs. Fouled plugs are not uncommon with the cooler operating temps of an a-4 using the 140 degree thermostat. You should also do an annual tune-up. It is especially important to clean or replace the points and plugs.
Fair winds with the new iron genny!