All books and articles which are an idiot's guide to the

functioning of carburettors start with a description of how a

venturi (or "choke") works - by lowering the static pressure of

the incoming airstream so as to suck up some fuel. This process

is not efficient, it is known in thermodynamic terminology as

"irreversible" - that is, you cannot get out of the process

anything like the amount of energy which went in. My girlfriend

is irreversible, for example.

In effect, the engine is strangled purely to provide some power

to drag the fuel in. Atomizing the fuel nicely (making a fine

spray) so as to make it evaporate better takes more power, a more

restrictive choke, which adds to the strangling effect. In

addition, the chokes and spray bars play havoc with shock waves

travelling up and down the inlet port, meaning that little

advantage can be taken of their ramming effect.

Worse, when a highly-tuned engine is "off the cam" and is

suffering from blowback, the incoming air gets fuelled three

times - once on the way in, again when spat out, and again when

dragged back in. This accounts for the "stand-off" phenomenon -

the cloud of petrol spray seen by carb bellmouths, totally

messing up the settings.

All of this doom and gloom begs the question, if chokes are so

bad, why not pump the fuel in under high pressure, so as to get

rid of them? The answer is that motorcycle design, even at the

highest racing superstar level, is heavily influenced by stupid

greasy oik stick-in-the-mud has-been old pillock luddite twats

who much preferred life in the days of an old tobacco tin full

of assorted jets, needles, and slides with different cut-aways.

Kenny Roberts once said that carburettors are bound to supply the

most suitable fuel mix for an engine as it then receives the fuel

supply which its suction demands. Many journalists believed this

and dutifully reported it, whereupon he must have gone back to

the bar for a good laugh with the Yamaha engine men.

When I was a development engineer working in the F1 car world, we

also used to have competitions to see who could get a journalist

to print the most ridiculous horseshit. My technique was to look

slightly worried whilst describing some complete nonsense which I

made up as I went along: it was amazing what the average hack

would believe then, and we could read all about it in the next

issue of Furry Dice Monthly.

Another aspect of Mr Roberts' management technique, which he

strangely forgot to mention in his superb book, is that when he

finds something particularly good, he will tell everyone else

that it is complete crap, thereby keeping the advantage to

himself. Expect to see a fuel injected Yamaha GP bike soon.

Page 2 of 8

The story which King Kenny put about is quite obviously false

even now: modern carbs (2- and 4-stroke) have emulsion tubes,

progression jets, power jets, air bleeds, and all sorts of other

complex contrivances to fool the engine and provide anything but

the mixture which it demands.

By far the most blatant form of this meddling with the "natural"

demands of the engine is the accelerator pump, which is actually

a transient form of mechanical fuel injection. If you don't

believe this, try opening the throttle with the engine switched

off - there is no venturi effect, but the fuel still squirts out.

Mechanical fuel injection was used in the car world on racing 4-

stroke engines for decades with moderate success. Typically, the

system would be not unlike an HGV diesel metering unit: a kind of

pump, driven directly by the engine, which therefore delivered

more fuel with increasing revs. The stroke of the pump would be

controlled by a shuttle linked to the throttle system, normally

with some sort of cam which allowed the part throttle fuelling to

be controlled quite well.

These systems never really translated into the bike world as they

only worked well over a narrow rev range and the pickup could be

rather abrupt. This is not a big deal on a machine weighing 500kg

with a pair of 15 inch rear slicks, but is a lot more dicey on a

two wheeler.

The Norton-Cosworth twin was one of several bike engines to ditch

a mechanical fuel injection system in favour of a pair of trusty

Amal carbs. What a bag of shite that thing was. Conventional

wisdom has it that poor management caused the death of the Great

British Motorcycle Industry: in fact, that Norton engine proved

that had the (highly esteemed) design engineers of the GBMI been

Japanese, they would have been ritually beheaded by their

shareholders. That even Cosworth couldn't sort that engine out

goes to show just how bad it was in the first place.

I worked in the Development Department at Cosworths for a while

during the pimply stage of extreme youth. In those days I lived

on beer and curry, my face looked like a pepperoni pizza and my

ringpiece like a sliced blood orange. I was even more short-arsed

then than I am now, and I used a Norton-Cosworth engine as a step

to allow me to reach things on the top shelf in the stores - this

is significant, as it is the only known case of one of these

engine units being anything other than a total waste of space.

The mechanical fuel injection system reached its height of

development in the early eighties, the last days of the Cosworth

DFV Formula 1 engine (Lucas mechanical injection) when the dog's

dick road car to have was the Audi Quattro, which had a Bosch

system, again totally mechanical.

Page 3 of 8

It was then that fuel injection really came of age, with the

increasingly popular use of microprocessor-based electronic

control units (ECUs). These allowed for huge flexibility in

controlling the fuel delivery, making the systems much more

adaptable than the older mechanical ones.

There are many concepts like this, which have been on the shelf

as Good Ideas for years, they are just waiting for the technology

to become available so that they can be made to work properly.

An example is the Wankel engine, which has been around as an

unreliable oily shitbox for ages, but has now been made viable

with recent advances in tip seal materials and lubricants. The

irony is that no sooner had it become workable than it was

immediately banished to the outer darkness again by the

environment people - a Wankel will never get through any half-

reasonable emissions test, and will surely be banned for everyone

apart from the military before very long.

I wonder if a certain member of the Great British Motorcycle

Industry has worked that one out yet? Probably not, they still do

not know how to install a carburettor after eighty years of


The coming of the ECU allowed fuel flow to be controlled

precisely by switching electrical shuttle valves (for that is all

that a fuel injector is) for an easily controlled amount of time,

thereby controlling the fuel flow. Most systems have a high-

pressure fuel pump which keeps the supply side of the injector

(known as the fuel rail) under pressure. A small regulator known

as an FPRV (fuel pressure relief valve) dumps excess fuel from

the rail back to the tank to keep the pressure constant, normally

about 3 bar or 50psi, though there are a few 5 bar systems


High pressure pumps are usually electrically powered, and made by

a very rich kraut called Robert Bosch. Some racing engines have

mechanically powered pumps, but these need to be spun over

electrically to pressurize the fuel rail before the engine can be

started, of course. Lucas make a superb one of these.

As a safety feature, on road going vehicles the pump is located

close to the engine to reduce the amount of high-pressure fuel in

the system, and the supply is designed to be cut off by a relay

in the event of an accident. Most cars have a low pressure or

"lift" pump just to get the fuel out of the tank and up to the

high-pressure pump.

Page 4 of 8

The first really good electronic injection systems were made by

Lucas. The ECU frequently controlled ignition timing as well, and

was then known as an Engine Management System, or EMS. At the

time, Lucas were world leaders in EMS technology, a reminder of

the great days not so long ago when an engineer knew that if he

couldn't find what he wanted in Birmingham, it would be a waste

of time looking around the rest of the world.

Some engineers at Lucas showed their warm appreciation of the

progressive and sympathetic management style there by buggering

off with all of the secrets to start their own companies, which

flourished. To this day, outside the group of big multinationals

who make their own systems (Lucas, Bosch, Marelli, Ford, Honda,

etc) there is a plethora of small specialists who mainly

concentrate on racing in a shifty sort of way because much of

their stuff contravenes Lucas-held patents. Lucas seem not to

mind too much as it all goes to help the sales of Lucas

injectors, pumps, FPRVs, etc.

The basic set-up of high-pressure fuel rail, injectors, and EMS

(normally known as the black box or brain) has changed only in

detail since the early Lucas systems. The main area of

improvement has been in the brain itself, with the availability

of more powerful and user friendly programming systems

(software), and faster, more sophisticated chips (known loosely

as "firmware", being neither hardware nor software. Really deep

people, electronics engineers).

The brain contains a series of instructions which governs fuel

delivery and spark timing; these are normally worked out

beforehand on a small computer and then "uploaded" to the ECU,

where they are stored in a chip for use. The first chips, known

as EPROMs (eraseable programmable read-only memory) were a bugger

to use as the only way to alter the program was by pulling the

chip out and putting a new one in. These could take anything up

to half an hour to prepare (the process known as "burning in").

It was then normal to see F1 engineers with little foam-lined

boxes full of chips, each with slightly different programs,

which they could swap with whatever was in the car when required.

My own experience of this system was that no matter how many

chips you had, none of them was quite right, so that meant half

an hour in the back of the transporter to burn another one in.

The other approach (especially with Italian racing teams) was to

stand around and argue passionately about which of the present

chips represented the best compromise, but this normally took

more than half an hour anyway.

Page 5 of 8

The Great Leap Forward was then the EEPROM, or electrically

eraseable PROM. This could be reprogrammed via a cable from a

portable computer, meaning that a new chip program could be

uploaded without any fiddly work in about 30 seconds. The cable

(or comms link in computer jargon) also meant that an ECU could

be controlled directly from the computer keyboard.

This is especially useful in dyno testing, when all engine

functions can be monitored, changed, and recorded on the

computer, and the chip only programmed right at the end of the

session. It is also possible to re-map car ECUs by driving up and

down with a lap-top computer on your, er, lap. I have done this

at 150mph in a racing Jaguar sports car whilst trying to cure a

misfire, but have not tried it on a bike yet - I might be crazy,

but I'm not stupid.

The writing of software for an EMS and the subsequent programming

of the ROM is a very highly skilled job demanding rare talent and

experience: my guess is that only about one per cent of those

people who think that they know how to do it really do, perhaps

no more than 20 in the world at the highest racing level.

What doesn't help is that there are only about five dynamometer

systems in the world good enough to keep up with the latest EMS,

so that tends to mean a lot of very expensive track tests.

Money must then also be thrown at telemetry systems, because most

test drivers and riders who are fast enough to be suitable seem

only to get their IQ levels into double figures when going

downhill with a following wind, and their feedback cannot be


This is a pity, because modern EMS systems offer truly awesome

control over engine functions, more than most engineers can use

at present. As is often the case, adaptability also brings

headaches, because with so many things to play with, so many

things that can be altered at the touch of a button, setups are

often way out and people just go around in ever decreasing

circles until either they disappear up their own arseholes or

they go back to carbs out of sheer frustration. Confucius said

that a man with a clock knows the time, but a man with two is

never sure.

All modern software for programming ECUs is based on what is

called the "map". A two-dimensional map is the easiest system,

often used for ignitions. A sensor on the engine tells the ECU

what the speed is, and the ECU will select the required spark

timing from that point on its map. Thus, the programmer must

enter a specific timing for every speed. To make things simpler,

the program will require to know the timing required at (say)

250rpm intervals, and the software will join the dots up to

decide what the timing should be between these intervals.

Page 6 of 8

The next step is the 3-dimensional map, where the spark timing

depends on another parameter as well as the rpm, normally the

throttle angle, which the ECU can again find out by means of a

sensor. Therefore, with a speed and throttle sensitive 3-d mapped

system, the EMS is constantly checking these two inputs to find

out what the spark advance should be by looking at the required

point on the map - say 11,000rpm up and 30% open across.

This is a very powerful tool; the advance for best power on full

throttle at any and every particular speed can be found by dyno

test and entered, the part-throttle timing can be advanced to

provide good response and mid-corner pickup, the low-speed low-

power setting can be retarded for easy starting, and a huge

amount of advance wound on for high-speed closed throttle (ie

overrun) conditions to stop popping and banging.

Normally, modern EMS systems have two three-dimensional maps

based on speed and throttle inputs, one map for ignition, the

other for fuel flow.

A typical 3-d fuel map will have high fuel flow for low-speed

wide throttle (starting mixture), smallish flow on half throttle

(to give a lean mixture for good economy and response) and a well

rich mixture for best power on wide open throttle. Entering the

fuel-flow values for every single point on a 3-d map takes ages,

and so normally only a few points are checked on the dyno and the

rest filled in by guesswork.

This is why many racing engines run like ruptured ducks at low

speed; the engineer simply couldn't be bothered to spend time

testing an engine costing L75,000 with a service life of about

400 miles under conditions which the driver would never use. As

maps for engines of the same type normally look pretty similar,

there is usually a standard map which is fine-tuned to each

engine in the important areas. "Important areas" on racing

engines are wide-open throttle in the powerband; for a production

engine "important areas" are idling and low-speed pickup, which

are normally adjustable by screwdriver to keep the luddites


You would think that, with the ability to fix fuelling and spark

advance at any possible combination of speed and throttle at the

touch of a button, all engine management problems would be

solved. The very first EMS systems did that, and were crap. There

is so much more to engine functions than a pair of 3-d maps, and

the surface has only been scratched. Again, the availability of

advanced electronic systems only makes life for the engineer

harder; it is no wonder that many just reach for the tin of jets.

Page 7 of 8

Perhaps Karl Marx had this sort of thing in mind when he wrote in