Really?

It's quite basic, it's called induction. A magnet spins in a coil which creates electricity from kinetic energy. When the engine is started by manual cranking, it can supply that kinetic energy to the magneto to continue operation. This can easily generate 12v which is what the ignition coil wants.

Obviously this actually requires a manual movement to get it started.

Quote from S14 DRIFT :

So hence why I presumed, rightly from my experience that a carbed vehicle which doesn't have fancy electronic components making it run either requires far less electrical power or can function without.

Jamie presumes rightly (?) from his experience that a carbed vehicle can function without electrical power...

Quote from RasmusL :

...

It is still electrical power that has to come from either a stored source (a battery) or a generator driven by the engine.

How did it even get to this argument Are we arguing whether an engine can run without enough battery power (or a battery at all), or without electrical power? Because conventional gasoline powered engines obviously won't run without any electrical power. But why is this even an issue? Obviously I began explaining the workings of a generator because it seemed to be about the battery dying.

If the argument is about whether an engine would die if the battery died - well, it MIGHT not if it was designed with a magneto driven by the engine. Or it might, if this magneto doesn't supply enough power to the ignition anyway. End of story

Quote from RasmusL :

Because conventional gasoline powered engines obviously won't run without any electrical power.

Exactly but as usual Jamie makes a really stupid comment without thinking about it (like rightly assuming that an engine will run without electrical power so long as it is fully carbed) from his 'experience' and then moan when somebody points out he's talking shit...

Quote from ajp71 :

Jamie presumes rightly (?) from his experience that a carbed vehicle can function without electrical power...

By which I meant without a battery. But yeah that's just me not being precise enough in my off the top of my head responses. Oh well.

Quote from S14 DRIFT :

No to be honest with you chum. I just know that the engine sucked through what it needed rather than being injected electronically what it was asked for.

Fuel from the bowl is sucked into the motor from the air flowing past the needle valve in the carb. But something has to fill up the bowls. You claimed that there are vacuum powered fuel pumps. I have not seen any. I think you are mistaken. The bowl is either going to be gravity fed, as motorcycle carbs usually are, or there's going to be a pump filling the bowl.

This image will help any discussion regarding the original question of fuel vs throttle vs rpm.

http://www.track-monkey.co.uk/KMS/kms_fueling_map_graph.jpg

As you can see the time the injectors are open only relates to the rpm and load loosely. Generally we can say that the higher rpm and load the more fuel is used but the link is weak at very low and very high rpm.

Maybe this can be explained because an engine will struggle to run at very low rpm because of lack of momentum so will require more fuel. And at very high rpm and load a nice lean mixture (about 12.5:1) is required for max power.

Every motor will require a different map depending on a multitude of factors. I could probably list hundreds of factors but things such as igntion timing, cam duration and lift, injector size, fuel pressure, fuel type, RON, MON, intake and exhaust design, head design etc etc would be included.

It doesn't really help in determining the best way to drive a particular car in order to achieve maximum mpg if that is part of the question. But my instinct tells me that for most motors lower rpm and light throttle position will achieve best mpg assuming the motor isn't labouring.

Speeds below that where wind resistance becomes significant (about 60-70mph) will help fuel consumption. Obviously 5th gear is better than 4th so I would say get up to speed as quickly as you can without using lots of throttle or high rpm.

Quote from Gentlefoot :

a nice lean mixture (about 12.5:1) is required for max power.

That'd be rich though. Approximately 14.7:1 is the stoichiometric ratio, you'd need more air to make it lean and less air to make it rich.

Other than that I agree with your conclusion, hence my saying "the only way to know is to get a read-out from the ECU". Monitoring the injection period and fuel pressure is as accurate as it gets, since you can't measure the flow after the injectors.

I don't think a purely mathematical solution exists (and probably never will because - sadly - we'll ditch internal combustion engines before anyone would bother) to accurately calculate the optimal (= most economic) operating conditions for any given situation. Gets even more complicated when forced induction comes into play... so yeah, "meh".

Quote from morpha :

That'd be rich though. Approximately 14.7:1 is the stoichiometric ratio, you'd need more air to make it lean and less air to make it rich.

I was always under the impression you would melt an engine pretty quick running it at stochio. But I'm not sure where I heard that so I could be wrong.

I knew I'd read it in a decent source. These ratios below are taken from A Graham Bell's Four-Stroke Performance Tuning (Second Edition). It's the bible as far as I'm concerned and I would recommend anyone serious about engine tuning to have a copy of this book for constant reference.

Starting - 1-3:1
Idling - 6-10:1
Low Speed Running - 10-13:1
Light Load Ordinary Running - 14-16:1
Heavy Load Running - 12-14:1

Quote from Gentlefoot :

I knew I'd read it in a decent source. These ratios below are taken from A Graham Bell's Four-Stroke Performance Tuning (Second Edition). It's the bible as far as I'm concerned and I would recommend anyone serious about engine tuning to have a copy of this book for constant reference.

Starting - 1-3:1
Idling - 6-10:1
Low Speed Running - 10-13:1
Light Load Ordinary Running - 14-16:1
Heavy Load Running - 12-14:1

Some engines run AFRs of 30-40:1 under idling, sometimes higher. Not race engines, mind, but we're not talking about them.

I can totally believe that with road car manufacturers trying to improve fuel consumption figures. Savagly lean mixtures at small throttle angles at cruising speeds and injectors completely closed during over-run.

Amazed they can make an engine idle at those mixtures though.

Keep in mind that it's a ratio of fuel to air. It doesn't tell you anything about the amount of fuel actually combusted, just that it's mixed with exactly the right amount of air to burn it completely.

Could be 0.01g of petrol mixed with 0.147g of air, but could also be 1kg of fuel mixed with 14.7kg of air.