# Benefits of Carburetor over Fuel Injection?

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1. Jul 8, 2015

### RaulTheUCSCSlug

What are the benefits of carburetors over fuel injection methods in engines? I have started working on motorcycles and have noticed that even modern motorcycles are carb'ed rather than fuel inject. Is it because of the cost of adding a computer? Or is there something else to it?

I know that some motorcycle companies tend to get away from modern technology to retain a brand image, but working on my carburetor on my motorcycle I notice how much I can change the fuel system just by changing the jets, shimming the needle, changing the air/fuel mixture etc. But for a fuel inject, wouldn't it just be connecting it to a computer, pushing some buttons and off you go?

Are there any benefits to carbs vs. fuel inject? Carbs seem pretty easy to work with to be honest, but I do understand that there is a bigger chance of wasting fuel. Also for cars and not motorcycles, how is it working with the carburetor?

2. Jul 8, 2015

### Dr. Courtney

Fuel injection allows the computer to be dialed in just right to reduce emissions, optimize power, or improve fuel economy, depending on conditions. If there were fuel economy and emissions standards for motorcycles as rigorous as for cars, I bet they would have a fuel injector and a computer controlling it.

Carbs are cheaper, more reliable, and easier to fix.

3. Jul 8, 2015

### RaulTheUCSCSlug

I am still unsure on how fuel injection works though, is there some form of diagrams that are available that can explain it more thorough? I know how a carburetor works since I've taken them apart myself, and seen diagrams on how they work, but have yet to work with a fuel inject system.

California motorcycles still have to meet EPA standards even if they are out of state.

Is there is a difference in price or complexity between EFI systems and direct fuel injection?

4. Jul 8, 2015

### RaulTheUCSCSlug

Also I believe that there are "lower" standards for motorcycles since they often have a better miles per gallon when compared to a car (unless you look at higher cc engines from 1200 and up). But I still don't comprehend how two stroke motors are still legal! All that oil burning cannot be good for the environment...

5. Jul 8, 2015

### Staff: Mentor

https://en.wikipedia.org/wiki/Fuel_injection

6. Jul 8, 2015

### jack action

Carburetor: A restriction creates a pressure drop in the air stream that pulls the fuel into the air stream. The pressure drops «tells» the carburetor how much air goes in such that fuel can be correctly metered.

Fuel injection: A pump is used to push the fuel into the air stream. Some measuring device must be installed into the air stream to measure how much air goes into the engine.

I would say that carburetor are simpler because they don't need a pump (the engine is the pump) and an extra measuring device. Fuel injection are usually less restrictive to the airflow.

You can have one central carburetor/injector or one carburetor/injector per cylinder (the latter being better than the other). You can also add to both systems electronic sensors to add precision in the metering of the fuel.

What turn most people to fuel injection in the 80's is due to a lot of «unfair» comparisons. Multi-injectors were often compared with single central carburetor. Most motorcycle already had one carburetor per cylinder, thus there wasn't much improvement going to multi-port injection for them. The other point was that electronic fuel injection was often compared with mechanical carburetor. But sensors and variable jets can be added to carburetors to do the same thing as injectors. But in all fairness, with all the electronics added, I think fuel injection gives an advantage in the packaging department. Marketing «new» fuel injection systems is also easier than selling «improved» carburetors.

Though, nowadays, fuel injectors are injecting fuel directly into the cylinders. That gives a huge advantage (better air-fuel mixing) that carburetors will never be able to accomplish.

Last edited: Jul 9, 2015
7. Jul 8, 2015

### SteamKing

Staff Emeritus
Carbs are cheap to make and work fairly well over the operating range of an engine. They are hard to start on cold mornings and can get flooded easily if the operator isn't skilled at working the throttle.

FI systems have been around since before computers got small enough to carry around. The mechanical FI systems used a lot of precision parts in order to function, which made them more expensive than most carb setups, except probably multiple carb engines.

Reciprocating aircraft engines were the first to use FI, because it eliminated a lot of problems related to keeping carbs functioning at different altitudes and under the motion of the aircraft, which can change suddenly and in three dimensions.

Outside of cost and ease of maintenance, there's not much.

FI systems are widespread on autos because emission controls and fuel economy are highly regulated by various local and national governments. If your cars can't meet these regulations, they either can't be sold legally or the manufacturer must pay hefty fines.

Electronic FI systems allow for the precise metering of fuel over a wide range of operating conditions, they are easier to start in cold climates (or even hot ones, where vapor lock might give carbs fits), and the sealed nature of the FI system means that less raw fuel is allowed to evaporate from an engine when it is shut off, reducing overall pollution.

8. Jul 8, 2015

9. Jul 8, 2015

### tom aaron

The old FIs were a pain in the butt. One of the criteria when I bought a vehicle...no FI. Today, in contrast they are much, much more reliable.

If I rode a motorcycle, I'd prefer a carb so I could tweak it. Take it off..,clean it. Part of the fun.

Yes, carbs had issues but nothing that couldn't be adjusted, fixed or replaced in a few minutes. Always used carbs, parts available. Many a lad started off with a bucket, brush, Varsol, repair manual flipped open to carburetor. Everything taken apart, cleaned , back together and fingers crossed when the key was turned.

10. Jul 8, 2015

### jim hardy

http://www.allpar.com/cars/desoto/electrojector.html
it has a good rundown on the differences.
the one 1958 Desoto left on the planet with its analog electronic fuel injection system intact.

I think you hit the nail on the head - simplicity.
If you have carb and magneto ignition there's no need for even a battery. Use the kick-starter( real motorcycles have one) or roll down a hill.

11. Jul 8, 2015

### SteamKing

Staff Emeritus
Yeah, Chrysler got tired of all the maintenance and warranty headaches with this system, IIRC, and developed a dealer-installed kit to convert the injection cars back to regular carburetion. Most owners took advantage of the swap, and with DeSoto being dropped soon after by Chrysler, time has taken care of the rest of these cars, save one.

The competing fully mechanical system developed by GM about the same time had somewhat more success. At first, it was available in selected models of full size cars along with sportier lines like Corvette, but its use eventually dwindled down to just that last model until 1965, when it was dropped for big block engines and multi-carb setups which were then proliferating. Still, surviving cars equipped with this FI system are rare today and highly prized by collectors. A second hand FI system in good condition can fetch upwards of $10,000-$15,000 alone today, with a few original new old stock (NOS) units still out there, commanding the highest prices.

12. Jul 9, 2015

### jim hardy

1957 ? Doubtless it was germanium transistors... Although the February 2003 IEEE Spectrum wrote an article describing it as vacuum tubes, i see no tube sockets in the photos. Can you imagine such an analog computer in automotive temperature environment?

Looks like a pair of transistor sockets underneath the circuit board.

Reports are it wouldn't start below 40degF..

Last edited: Jul 9, 2015
13. Jul 9, 2015

### SteamKing

Staff Emeritus
I think the electronic control unit on the Bendix/Chrysler Electrojector EFI was built from discrete components, since this system pre-dated the invention of integrated circuits as we know them today.

According to this SAE paper from 1957, written on the development of the Electrojector system, p. 760 in the available preview,

http://papers.sae.org/570060/

Bendix engineers first prototyped the ECU using vacuum tubes, but they soon found that tubes take a while to warm up before they can function. The production ECUs were re-designed to use transistors in place of vacuum tubes, hence their absence from the photo of the innards of the ECU. Tubes also required a relatively high current draw from the battery while the system warmed up. Apparently, the development of the ECU resulted in at least 4 different models, including the tube prototype, with each succeeding model getting smaller and drawing less current for operation.

14. Jul 12, 2015

### RaulTheUCSCSlug

Now this is exactly what I wanted to hear, not just be directed to some wikipedia article. Thanks for all of your input and definitely helped me gain some more knowledge on the subject!

15. Jul 12, 2015

### jim hardy

Thanks !
I have a soft spot for those Chryslers. My friend's grandfather had a '57 New Yorker with the 392 hemi, you'll see it in the first Godfather movie scene where they visit the old guy in Miami Beach - black 4 door , big fins...

Its acceleration was incredible for the day.

Somebody mentioned the "sealed up" natue of FI.
I have a '03 Ranger that sits sometimes for a year between starts.
The system stays full so it always starts in one crankshaft revolution.
A carb would have evaporated dry and probably gummed up.

16. Jul 12, 2015

### SteamKing

Staff Emeritus
That's one of the benefits of FI. As long as the system is functioning, and there is gas in the fuel line, the engine will start in just about any weather, hot or cold, since you get the fuel delivered already atomized by the injectors.

The one draw back is that most cars and trucks equipped with modern EFI systems have an electric fuel pump installed in the gas tank, which keeps the fuel system pressurized. When those in-tank fuel pumps need replacing, man, you've got a job pulling and replacing that pump. The older mechanical FI systems didn't need those in-tank pumps and could work with a standard fuel pump mounted on the engine.

17. Jul 13, 2015

### RaulTheUCSCSlug

Why the change in design to the fuel system?

18. Jul 13, 2015

### SteamKing

Staff Emeritus
There are several reasons.

The engines which used the mechanical FI systems had been designed to use carburetors initially, and the engineers designed the mechanical FI systems to fit with a minimum of modifications to the existing fuel delivery system coming from the fuel tank.

Carbs do not require fuel pumps with high delivery pressure and are fitted with a small fuel bowl to allow for excess gas storage. Fuel pumps could be driven mechanically directly from the engine by using a simple lever actuated by a cam attached to the crank or cam shaft, which pressed onto a diaphragm, pumping fuel from the tank to the carb.

EFI systems require a pump which can deliver fuel at higher pressure than required by a carb and at greater flow rates. The older mechanical pumps could not perform effectively, so they got replaced by electrical pumps which did not need to be driven mechanically by the engine. Because of this, and due to cramped engine compartments in most cars, engineers could move the fuel pumps away from the engine and mount them instead in the gas tank. The FI equipment mounted on the engine typically has no reservoir for any excess fuel to accumulate, so a fuel return line back to the gas tank must be provided to prevent excess fuel from building up in the system.

Electric pumps can also pressurize the fuel system almost immediately when the ignition switch is turned on, unlike mechanical pumps which must have the engine turning in order to produce any pressure. Electric pumps eliminate the need to crank the engine to pressurize the fuel system before starting.

19. Jul 13, 2015

### jim hardy

When i was in high school(1961) a friend dragged home a 1931 Model A Ford. It was only thirty years old at the time...

It does kids a lot of good to bring one of those back to life.
Carbureted of course,

spark advance is manual by a lever in middle of steering wheel,
three brush generator so there's no voltage regulator,
fuel tank mounted up behind the dashboard so gravity suffices for a fuel pump,
fuel line is the white tube from upper left to carburetor bottom center.
http://oldcarandtruckpictures.com/ModelAFordRebuild/1928_Model_A_Ford_Model_60B_Leather_Back-nov10h.jpg [Broken]
http://oldcarandtruckpictures.com/ModelAFordRebuild/ [Broken]

We learned our basics on something simple enough for fourteen year olds to figure out.

But - should you ever get one - upgrade the mechanical brakes to hydraulic.
We often resorted to the emergency brake , for emergencies like stop signs.

Last edited by a moderator: May 7, 2017
20. Jul 13, 2015

### RaulTheUCSCSlug

Oh man, those must have been the good old days! Interesting with the brush generator, and if the car was run to higher altitudes, was it just rejetted?

21. Jul 13, 2015

### jim hardy

I grew up in Miami where 20 feet of elevation was a mountain.
I don't know about Model A's, but for Flathead V8's(1932 to 1953) Ford parts department sold a "high altitude kit" consisting of resized high speed jets and a power valve with different spring. I tried one when in Colorado, couldn't tell that it helped, still 15mph over Berthoud Pass..
That's one place where fuel injection shines, above 10,000 feet.
I'm not quite sure why probably to do with venturi effect. With FI, throttle body doesn't need a reduced throat area to induce fuel flow so you don't have that flow restriction.
Perhaps a genuine mechanical engineer will chime in.

22. Jul 13, 2015

### tom aaron

I heard a panel discussion on space technology. The success of Apollo was largely attributed to engineers and others who had learned perspective by tinkering as youths with a bicycle, Model T, the family tractor, etc. The guys who emerged from both sides during WW2 when the mantra was 'just get it done'. Von Braun and others were as handy with a wrench as they were a Slide Rule.

23. Jul 13, 2015

### jim hardy

i kept this poster over my desk for years

"Before there was a high tech, there was a low tech"

credit to the artist http://www.greenwichworkshop.com/christensen/lowtech.asp#bio

24. Jul 13, 2015

### SteamKing

Staff Emeritus
Sadly, this hasn't been the case for a long time.

I remember taking my car in for service, probably 30 years ago now. The young attendant at the service station (Remember those?) was trying to check the fluid in my car's manual transmission (it was ATF instead of gear oil; long story about that). To check the fluid level, all one had to do was take out one bolt from the case and stick a finger in to see if the fluid was there. The poor boy doing the service could not remember which direction to turn his wrench to take the bolt out. Fortunately, I was watching him while he did his work and was able to stop him before he stripped the threads on the aluminum transmission case.

The skills taken for granted in older times are largely lost on the newer generations who use only their thumbs.

25. Jul 13, 2015

### tom aaron

Yes, it's a difficult balance. The KISS principle disappeared with the Space Shuttle and James Watt Telescope. Someone needs to actually turn the nut on the bolt in addition to some computer simulation of the part involved.

Probably no longer the case but one of the first things the Israelis did when receiving military jet fighters from the USA was to customize them...not adding but removing features...simplifying.

On the positive side we can send a probe to Pluto with pinpoint precision...incredible. Fix the television?