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EFI vs carb


Gettin'old

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So I'm assuming EFI has the advantage in most categories, newer tech, more power, etc. How do these two fuel systems compare when it comes to fuel economy? Any other advantages or drawbacks to one or the other?

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A very common misconception about EFI is more power, that is actually not true, in fact a carbed engine can deliver more power than an EFI unit, seen many examples on the dyno.

Advantages for EFI: economy, driveability, starting, cold running, hot running, no tuning requirements, fewer emissions.

Advantages for Carb: power, simplicity, cost, no high pressure fuel pump, easy to rebuilt and tune.

For a boat that spends most of its time at a steady speed, a carb is not a bad device and the fuel injection does not have as many advantages as it does for an automobile.

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Not long ago got out of a carby engined boat and into a EFI boat. The carby boat was a Gilflite Shortline 190, a top Australian ski boat, 19ft long and powered by a 400ci small block Chev with 650 double pump Holley which we used for skiing at 32 - 35mph. The 400 gives heaps of torque and very reliable. Estimate on HP was about 300 - 310hp. Two years ago I purchased a Response with the 335hp Monsoon. I thought that with a smaller fuel injected engine fuel consumption in the Response could be less, but it works out about the same. Could be the extra 400 kilos weight the Response has over the Gilflite. In saying that though the guy I ski with has a Sportster with a 310hp Vortec carby engine and I swear it uses less fuel than the Response!!

Very impressed with the low end torque of the Response, pulls just as well as the Gilflite.

Advantages I see that the EFI has are,

1. Cold start, fires up instantly and runs perfectly until warmed up.

2. Smooth running, no flat spots or tuning needed.

3. Safety, always worried me having a carby, fuel leaks the risk of a back fire etc. Never had an issue but it was a worry. Every summer one or two ski boats would burn to the waterline in our general area.

An interesting point though, both boats use less fuel than the 115hp Johnson outboard that we used to have powering a 16ft ski runabout. This was a carby, 2 stroke OB but I believe that the new EFI 2 & 4 stroke OB's are far more efficient.

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EFI advantage: wife and guests can start boat 100% of the time. I have yet to be in or have owned a carbed boat that did not have a "personality" at start-up.

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Ease of use and starting.

Yes carbs can produce more power in the right tunning. But the tunning can change with humidty, temperature, altitude, atomospheric pressure, etc.

My last boat had a 454 square port 400hp engine in a supra. It was a beast but at the same time was a pain to keep tunned and was cold natured.

My indmar mpi 350 is a dream in comparrison. Idles smooth always fires the first pump of the switch and does very well in fuel.

Even look at merc's new turbo 1350hp it's injected.

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Carbs are used for one reason - they are cheap. Less wiring, nothing computer controlled, just slap the carb on and go. A properly designed EFI manifold will flow just as well as a carb...that's not to say most EFI manifolds are designed for optimal flow.

Even in racing, carbs are used because of rule restrictions, not because they are the optimal way to go.

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  • 10 months later...

I copied this from another forum. We had a 1989 Malibu Sunsetter, Euro F3, Rochester Quadrajet. It ran perfect for 20 years. Yes, it took a few turns to start cold, but after I learned to pour a little gas down the carb it started like a fuel injected engine. We started having inconsistent idle problems so I rebuilt the carb, the local shop rebuilt it, still had idle problems. Thought I found the problem when I found tons and tons of carbon on the back sides of the intake valves. This engine had 950 hours on it. So I rebuilt the top end, new exhaust manifolds and all new hoses. Still would not idle consistently. I double checked for vacuum leaks and did not find any. I decided to add TBI fuel injection and bought a kit from "Affordable Fuel Injection" - $1620. What a mistake. The only improvement was cold start. Everything else was a nightmare. It never idled correctly and would die when placed in gear sometimes, could not be relied upon. This is really tough when pulling up to a dock or trailering it. This engine never died with the carb, never. It also had a very bad flat spot at around 2800 - 3500 RPM, flat out would not run between 2800 and 3500 RPM. It was a nightmare trying to hold skiing speeds with the fuel injection. AFI reprogrammed the chip several times with no improvements. We used it for about 2 months, saw no improvement in efficiency, if you ran it at higher speeds, it seemed to use more fuel than the carb did. No difference in power/speed. I returned the unit within the return policy, AFI "repaired it" and sent it back to me. They kept saying I installed it wrong. They would not return any money. They do not stand behind their warranty and will not accept a return, so don't even think about doing business with them. I reinstalled the Quadrajet and it ran just like before. We traded it in on a new 2013 VTX, I was honest with the dealer about the problems it had.

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