Fuel Injection vs. Carb

[cwhite6]

I have a couple of dumb questions relating to fuel injection and carbs on I/O motors. I am looking at getting a bigger boat we can tube behind in the next couple of years and I am kinda confused.

1. Is fuel injection safer than carb? As in, you do not have a float bowl with fuel in it with fuel injection and other related piping. Are the fumes less than carb motors?

2. I have noticed the horsepower numbers for fuel injection are always higher than carb. Why is that?

3. Are the fuel injection systems easier on maintenance than the carb systems?

Thanks!!

 

[ezmobee]

Re: Fuel Injection vs. Carb

All that and more. I can't imagine a more worthwhile upgrade.

 

[Woodnaut]

Re: Fuel Injection vs. Carb

Electronic fuel injection was a revolution in the automotive industry. It lead to much cleaner and more economical operation. EFI and carbs are different, and therefore require different maintenance.

On fuel injected systems, the fuel has to be kept clean and free of water. Just keep top quality fuel filters and additives in the system and life will be good. The fuel tank filler inlet and fuel tank vents need to be positioned (and maintained) so as to not permit the ingress of water.

As far as safety, the fuel pressures are higher with EFI, but hoses and fittings are designed to safely operate at these higher pressures. All hoses ultimately deteriorate with heat and age, but routine replacement and maintenace is to be expected on any system.

It's true that many folks can dismantle a carb and give it a good cleaning when thing require a little attention. With the injected systems, there is sometimes a little more "replacement" and a little less "reconditioning". However, in my experience, there is a whole lot less maintenance in general on the injected systems. I really prefer fuel injection over carbs on all except for the smallest of engines.

 

[cwhite6]

Re: Fuel Injection vs. Carb

So, I see the 4.3 MPI and the 5.0 carb both have the same horsepower ratings. Would they burn a like amount of fuel? I am looking at a Glastron GT205 if that makes a difference. Biggest boat we are looking at is a 20 footer. Would the 4.3MPI push that boat good? Thanks.

 

[Chris1956]

Re: Fuel Injection vs. Carb

That 20 footer, is probably OK with a 4.3 MPI, provided it is not a heavy boat like a cuddy.

Although I agree that EFI was very good for the auto industry, I do not think it raised economy drastically however, it did cut maintenance. Fuel economy increases were additionally due to cutting weight, radial tires and aerodynamics, as well as stratified charge engines, 4 valves/cylinder, fuel charge "squish" design motors etc.. Boats have been given some of these advantages, but not enough since the marine environment is very hard on electronics.

You do see an EFI car burning profusely, everyone once in a while. Sequential Automotive-type EFI hoses are pressurized to 35PSI or more. If one of these rupture (very rare occurance), gasoline is sprayed onto the hot motor and whoosh...

 

[05GlastronSX]

Re: Fuel Injection vs. Carb

That 20 footer, is probably OK with a 4.3 MPI, provided it is not a heavy boat like a cuddy.

Anything less than a 5.0 mpi or a 5.7 is worthless in a 20 footer. A v-6 will be miserable on it. My friend has a 19 foot crownline with a 5.0 carb and its an absolute dog out of the hole, midrange ect. My glastron with a 150 outboard feels like a ferrari compared to any other I/O i have driven/experienced. There is no beating a 2 stroke outboard v-6 for shear fun. My boat gives you a good neck snap at any speed while you cant get that from an i/o.

 

[This_lil_fishy]

Re: Fuel Injection vs. Carb

No worries, I have that exact boat (see sig) with the 4.3carb version. It runs about 50mph but is under-propped (I over-rev at 5200rpm with four adults aboard at 48mph GPS) and this may improve with the proper prop. I run these speeds with four adults, but don't regularly ski or tube. So I dunno, typically with for adults I am on plane within three seconds of full trottle. Again hole shot would not be so good when towing a tub or skier. So it really is a matter of how much you can afford. Obviously the 5.0L MPI would be prefered, but I am very happy with my little 4.3. Of note, even after a full day of cruising/speeding across the lake I'll use less then a quarter of a tank (~35Liters). There is some argument that the big V8 will have more horsepower with the same mileage, which is entirely possible my new truck (5.4 L) gets much better mileage then my old truck (4.6 L). So who knows, so again, it comes down to what you would be happy with and can afford. I think you'll find the V8's have higher resale..but that's becuase it costs more to buy too.

I would have liked the 5.0 L carbed for sure, and as was said, electronics don't like water...also I am a backyard mechanic. Fixing a fuel injected engine requires special diagnostic tools, that I just don't have. Pulling a gummed up carb apart is a 30 minute job for me...so to each their own.

Ian

 

[dontask]

Re: Fuel Injection vs. Carb

One of the reasons injected engines gained mpg ratings is that in cars during deceleration-- a carbed engine would still pull a mixture of fuel in as the engine is slowing down (wasted fuel). The fuel was not able to shut off since the venturi action still pulled unneeded fuel in with carb set up. In injected systems the fuel can be shut off or greatly reduced, just enough to maintain the engine running. Since boats do not decelerate or coast as often as cars (stop and go traffic--coasting, going down hill) the gain in mpg would not be as much in a boat as a car. Injected engines have better computer systems to control mixture based on different inputs and parameters. Carbed engines don't have the ability to change mixture (pulse modulation) like computer controlled injectors can. Injected engines can lean the mixture out when it is able to, as it monitors map, temp, rpm's, throttle position, knock sensing.

 

[Bifflefan]

Re: Fuel Injection vs. Carb

The fuel was not able to shut off since the venturi action still pulled unneeded fuel in with carb set up.

This not true.
When you let off on a carb engine it closes the butterflies to an idle posotion and you are only using the amount of fuel the engine would idle with. Nothing is coming throught venturi's at this time.

 

[a70eliminator]

Re: Fuel Injection vs. Carb

Yea I was thinking the same thing.
Neverthless fuel injection is more efficiant, so are the electronics. Although I was surprised to see how many boats still used carbs and points ignition even into the 90's, basic and simple that's how we like it.

 

[dontask]

Re: Fuel Injection vs. Carb

This not true.
When you let off on a carb engine it closes the butterflies to an idle posotion and you are only using the amount of fuel the engine would idle with. Nothing is coming throught venturi's at this time.

Idle fuel not needed until the engine is at an idle speed (is wasted). Just like a vacuum pump the engine does not care where it is getting volume. As the engine decelerates it is pulling a higher vacuum on the idle jet due to the position of the idle jet outlet relative to the throttle plate. The time it spends in deceleration pulling unneeded fuel is wasted fuel. Notice when you let off the throttle in a car it does not go from 2500 rpm's to 750 in a split second, now multiple that period of time over and over again during a days driving. You say nothing is coming through the venturi's?????, the engine by design still wants to pull volume from anywhere & in this case the idle jet and a richer mixture than it needs to be. Next time you rebuild a carb look at where the edge of the throttle plate is in relation to the idle jet orifice. There are two ways to create low pressure to get fuel from that jet orifice, one by venturi design (Bernoulli's principle) or an evacuating pump which is what the engine is becoming during deceleration.
There was a J3 Cub engine produced that did not come with a choke (manual or automatic). The engine starting instructions when cold to enrich, were to leave the throttle at full idle stop and crank. At that throttle plate position it pulled (via evacuation, no velocity needed) more fuel from the idle jets than if the throttle plate was open. Then after cranking numerous revolutions you advanced the throttle it would start. There was not enough of the Bernoulli physics to deliver enriched fuel using the venturi effect. This "closed" throttle process was a way of priming. Do you understand how a dirty restricted air cleaner causes worse fuel mileage? Unless the law of physics changed over the years carbs still work the same way. Please let me know where you got your information I would like to research it.

 

[cwhite6]

Re: Fuel Injection vs. Carb

Thanks for all the answers guys! I appreciate the clarifications.