What makes this engine consume too much fuel is it the carburetor or pump or the engine it self.

You don't get anything for nothing - performance has to be paid for - in fuel!

Diesel engines run at much higher cylinder pressures than petrol engines, and the specific fuel performance is better, so the diesel engine is 'more efficient'.

In return, diesels that are not turbocharged are 'sluggish' and have lower top speeds (in revolutions), but they have superior torque - especially at lower engine speeds.

There's nothing 'wrong' with your petrol engine, but it will rev more freely (and faster) than a diesel engine. You will accelerate faster - but use more fuel . . .
As I stated - you can't get something for nothing.

If you avoid 'screaming' the engine and using full throttle pedal you can reduce the fuel consumption - but you will never match the economy of an equivalent diesel engine that is driven the same way with the same vehicle performance.

Altering the carburation isn't really worthwhile - engineers have spent many hours matching the carburettor to the engine to achieve optimum performance, and fitting a smaller one (as you suggest) will upset the balance and you risk damaging the engine if it runs too lean - and you will certainly lose performance.

Make certain that you have cleaned the air filter (if this becomes blocked it will increase fuel consumption).

Keep your tyres correctly inflated (slightly higher pressures will be better than running soft tyres).

what is LPG piper141 is talking about.

Hi the LPG that I was talking about is Liquid Petroleum Gas or Propane. Propane works better in lower temperatures as it has a much lower freezing level. I don't know if it's an option for you in the UK. In NZ a lot of Bedfords were converted to LPG in the eighties CNG (Compressed Natural Gas) was also used although range is shorter and there were tuning problems with it. LPG in NZ is 110 octane rated but also a lot cheaper $1.29 per litre v's 2.20 per ltr for petrol.

Hi bedfordman could you send me a photo of cab kind regards Lorenzo

Hi, if you still have the cab, then I'm interested. Thank you