Hi, thanks to you both. I'm happy to run the blower continuously -
just don't want it be used to hide something.
Understood.
Have asked they check everything again including did they create a small exhaust manifold leak when fitting the new inlet manifold.
have also spoken with a boat safety guy (in the UK) and he's suggested the fan has to be both continuous rated and 'ignition prrotected' too. I've asked them to check and/or replace my existing fan unit.
Make sure that you DO NOT use one of the In-Line or Turbo style blower motors.
They are JUNK, very noisy and live a very short life.
In stead, use a squirrel cage style in the continuous duty model.
my petrol vapour alarm is very sensitive - my understanding from their info is that it's triggered at 10% of LEL. It's probably perfectly OK and I'm now thinking that with the fan running always if the alarm's AOK (if triggered then it must be a real problem and stop immediately and investigate).
Regarding the fuel pump we don't have to stop the pump due to no oil pressure here
While this is a USCG requirement here in the US, it should be a standard throughout the world.
Worst case scenario:
.....Your fuel line becomes severed or disconnected.
.....The engine eventually stops.
.....Fuel pump continues to operate while fuel is being pumped into the engine bay.
.....The gasoline ignites, catches the boat on fire, you and/or your family and friends become severely injured, law suits occur, your Marine Insurance Policy does not cover the incident due to "negligence", etc. etc. etc.
With a very simple to install N/O Low Oil Pressure switch and relay, this is avoided.
(and you must need an overide button to get things started)
Also very simple.
You have two choices;
1..... trigger the fuel pump relay with the starter motor solenoid circuit. The relay prevents "back-feed".
2..... trigger the fuel pump relay with a "momentary helm switch". Must be a "momentary" switch in order to be legal here in the US!
(I like this one best because you can prime the system without operating the starter motor)
and I was thinking of just having an oil pressure failure buzzer instead (still got the original light plus pressure gauge). What's their reason?
See above!
The electric pump now fitted was sold by the weber supplier as a matching item (2.5 - 4.5psi) to the 32/36. With the engine not running but the pump running e.g. no oil pressure because of a problem or not yet been started is there any chance the pump might overcome the float controlled valves in the float bowl?
The carburetor would need to be equipped with a float sensing circuit that would somehow be tied into the pump's relay.
I have not seen anything like this for a carbureted engine.