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Which is easier to inspect, adjust & maintain the correct fuel mixture? F I or carb. ?

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That's an easy one, Cyclo - There's a reason why, for the most part, Fuel Injection has basically replaced carbs in the engine world. I know certain applications still use carbs but for everything you have to do less of, FI is the way to go. You have much better fuel efficiency, you get the best burn rate and mixture of air and fuel. Much less maintenance. Draw backs are that usually the injectors are pretty big bucks if you have to replace them along with control modules and injectors tend to run better on higher octane fuel which is more money. Carbs are stinky, finiky, like a diva part of the engine lol. Smell awful, affected severely by temperature fluctuations etc. Always go with FI.

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A carburetor at it core is a complicated, mechanical device. Idle circuit has fixed mixture screws that do not comprehend changes in air density, or atmospheric temperature. The idle stop screw just leaves the throttle plate cracked enough to let air in and attempt to manage the fuel being arbitrary dumped into the mix. It does not look at air conditions and engine temperatures, and must use an archaic devise known as the choke to provide an overly rich mixture to a cold engine just to get things started.

When throttle is transitioned from off idle to cruise, the accelerator pump squirts a shot of fuel just above the throttle plate in an attempt to off-set the gulp of air the intake manifold is about to see. No precision here, just a squirt based on linkage movement, not measured engine need.

Now the process has begun, but the air velocity is still not enough to draw gas through the main jet, up through the venturi's, as that takes time. Enter the power valve. Loss in manifold vacuum due to the opening of the throttle plate causes the power valve spring to shove the valve open and the fuel flow to begin. Again this volume is fixed, arbitrary, and totally mechanically biased with no regard to calculated engine need for a given set of conditions. Eventually the main circuit kicks in which draws fuel through the main jets, and creates partial atomization through the venturis.

Multi-port injection looks at ambient air temperature, atmospheric pressure, and engine temperature and optimizes fuel delivery based on precise measurement of throttle position. Air/fuel ratio can be optimized throughout the entire operating range of the engine, being adjusted at a rate of over 100 times per second. Cold engines require additional fuel and MPI meters just enough based on present conditions. Turn the key and drive away. High temperature, high humidity days mean low oxygen levels. Less air available means less fuel required. Instant adjustment. Cool day with a high barometric pressure means more oxygen, more potential horsepower, and more power for the fuel consumed. Again, instant adjustment, enhanced performance, and increased fuel economy. These eventualities are mutually exclusive when dealing with a carburetor.

To make MPI work, you need a computer, and although these things are a virtual black box full of magic, they are incredibly reliable. If you follow both boating and automotive forums, most times an owner decides to replace an EMC, it's because they failed to find the real problem in the first place. The other comments I see on our forum are mostly based on the fact that people react to hearsay and innuendo. Buy the manual for your system, read it, and forget what you have been told. You are dealing with an ECM, fuel injectors, throttle position sensor, manifold air pressure sensor, air temperature, and in most cases 4 water temperature sensors which you will have on a modern carb'ed engine anyway. The new O2 sensors on marine applications allow for even more precise fuel metering as they constantly monitor the air/fuel ratio in real time, and fine tunes the baseline fuel delivery. When they do need repair which is seldom, one just needs to test more and replace less. I like to think of it as closing the tool box and opening the mind. Carpenters call it measure twice, cut once.

Bottom line, you will not get the economy, max performance, and drive-ability and ultimately reliability out of a carb that you will from MPI. A side benefit of less fuel contamination into the engine oil due to cold operation over-fueling is increased engine life. Injectors linked to a high pressure secondary fuel pump atomize the fuel and introduce the mixture just before the intake valve. Precise delivery in real time. Keep synthetic oil in the crankcase, clean fuel in the tank, and you will see 2,000+ hours show up between overhauls. Try that with a carb.

W

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First lets get something straight. The fuel injection used on boats is not like what's in your car. The fuel injection used on boats in the model years 2013 and older are using 1970's technology. Speed density with no o2 sensors. Pre-programmed maps that can only stay within the parameters of the maps programmed to the ECU via a pressure sensor. The fuel injection system has no idea if it's running too rich or too lean.

You're not going to see any increase in fuel economy using fuel injection over carb on the same engine. If you have a Chevy 5.7 350ci using a 600cfm carb or Fuel injection they're both going to use the same amount of fuel at any given RPM to produce that power. You can argue that well, fuel injection is more efficient because it supplies the correct amount of fuel right? Wrong. Marine fuel injection up to only 2013 was batch fire. That means it sprayed fuel in the engine even when it wasn't on an intake stroke. MEFI4 and below literally wastes fuel down the drain. Compared to a highly tuned carb, zero benefits in terms of fuel consumption or power.

Why is the fuel injection/carb argument not applied to boats like it is cars? Easy. On your car you're literally changing the throttle position 100 times a minute. If not more. How many times do you change the throttle position on your boat? Once every minute? Once every 15 minutes? Longer? This is where carbs shine. They can be insanely efficient in constant throttle applications. That's why 99% of all drag racing cars are carbureted.

There is a time and a place for technology I understand, but due to how boats work in the quest for best economy the answer is not more technologically advanced gasoline engines with miles of wiring and ECU's. The answer is diesel power. Always has been, always will be.

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This is not true when it comes to boats. You're not going to see any increase in fuel economy using fuel injection over carb on the same engine. If you have a Chevy 5.7 350ci using a 600cfm carb or Fuel injection they're both going to use the same amount of fuel at any given RPM to produce that power. You can argue that well, fuel injection is more efficient because it supplies the correct amount of fuel right? Wrong. Marine fuel injection up to only 2013 was batch fire. That means it sprayed fuel in the engine even when it wasn't on an intake stroke. MEFI4 and below literally wastes fuel down the drain. Compared to a highly tuned carb, zero benefits in terms of fuel consumption or power.

Why is the fuel injection/carb argument not applied to boats like it is cars? Easy. On your car you're literally changing the throttle position 100 times a minute. If not more. How many times do you change the throttle position on your boat? Once every minute? Once every 15 minutes? Longer? This is where carbs shine. They can be insanely efficient in constant throttle applications. That's why 99% of all drag racing cars are carbureted.

There is a time and a place for technology I understand, but due to how boats work in the quest for best economy the answer is not more technologically advanced gasoline engines with miles of wiring and ECU's. The answer is diesel power. Always has been, always will be.

I just don't see that in practice. The 496 crowd I run with that are carb'ed can't come close to my fuel economy, and as far as drive-ability goes, they sit at the dock looking for engine heat before they dare make a move. Their crank case oil looks like black paint at season's end, and mine looks like I just put it in the thing. They keep up on maintenance and the carbs are as healthy as a carb can be. I just replaced the plugs after 6 seasons, and really did not need to. My carb friends are on a two year max cycle, as they start to loose both performance and economy.

W

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There has never been a 496 to ever roll off the showroom floor with a carb in boats or cars. That is a Vortec truck engine that was released in 2001 and discontinued in 2009 by GM.

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I love carbs. I like taking them apart, I like putting them back together. I like changing jets. I like adjusting them. All the boats and motorcycles I've have had, have been carbureted. I don't have a clue on how to adjust fuel injection, I always thought they were just magic, they adjust themselves. What fun is that?

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There has never been a 496 to ever roll off the showroom floor with a carb in boats or cars. That is a Vortec truck engine that was released in 2001 and discontinued in 2009 by GM.

?

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The 496 8.1 liter engine has never. Ever. EVER. Been installed in a boat, car, motorcycle, gokart, scooter with a carburetor. To say the "496 crowd" with carbs is having trouble is bull@#$%@# because there has never been a vessel powered in the history of mankind that has rolled off the factory floor that has ever been powered by a 496 with a carburetor.

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My 2002 5.0 L carb has 190 ? hours. Nothing has been adjusted or repaired. Up state N Y We did change spark plugs at 6 years. Looked great. Still look new now.

All the gauges read the same as new. I have a good carbed boat.

Hope we all get good ones.

I forgot. It has never had any dealer P M work done to it. Filters & oil changes each fall.

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The 496 8.1 liter engine has never. Ever. EVER. Been installed in a boat, car, motorcycle, gokart, scooter with a carburetor. To say the "496 crowd" with carbs is having trouble is bull@#$%@# because there has never been a vessel powered in the history of mankind that has rolled off the factory floor that has ever been powered by a 496 with a carburetor.

Wrong once again.

http://www.dragtimes.com/video-viewer.php?v=K_NwlRs_H4U&feature

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I have 400 hours on my 5.0 carb and it runs better than factory specs. I get 5 MPG at 30mph. Beat that with your fuel injection. You can't.

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I have 400 hours on my 5.0 carb and it runs better than factory specs. I get 5 MPG at 30mph. Beat that with your fuel injection. You can't.

Next time your in Michigan look me up....will drive circles around your carb with the EFI all day long and beat ya at the fuel dock also.

I turn the key and go while you pump the throttle and wait for it to warm up.

GROW UP ALREADY.

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Do you have hard paperwork specs to back that up? I do. Talk to me like an adult not like a child and come with proof or goto bed.

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Brian is right. His F I WILL go in circles around your carbed boat. The Computer has a panic attack & locks into a circle. No way to deprogram the ECMs. Fact

:)

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To answer your question CY. No adjustment without being able to reflash the computer with an EFI so it can't get any easier then that. Carbs are ok but can be temperamental as can the EFI. So its a blondes vs Brunete Merc vs Volvo . Both Have a purpose and both have good and bad points. I personally love my EFI.

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What? Brian, don't let them wear you down as if it's actually a 50/50 choice in the mind of the rest of the world. This idea that carbs are better is pure lunacy. What's next? A black n white TV is really better than a color flat screen? Please. I'm sure the best automotive engineers at BMW, Porsche & Audi are trying to figure out how to put carbs on their new offerings. Ditto for Merc & VP. It's insanity.

I would keep going and list reasons to support this, but I've decided that these iPad thing's are not as good as my hammer and chisel so, I'll be hammering it out my list of why FI is better and then drag the slate of rock into the back yard. You'll have to get into your horse drawn carriage and ride for days or weeks to read my response.

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I'm beginning to think Ric is trying to compensate with these ridiculous posts.

This guy spouts about all this high performance engine knowledge he has yet he readily admits he's got one of the smallest boats Chap makes with the smallest engine available. He complains about the lack of power yet even with all his skill and knowledge does nothing about it.

Plain and simple, Ric has a case of boat/engine envy.

He yearns for a bigger boat with a fuel injected big block but for whatever reason is unable to own one.

So, he compensates by telling us how smart he is and how much better life is with a small underpowered (carbed) boat. :)

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Hey Ric, what about EFI boat engines post 2013? If your whole argument is about EFI engines pre-2014 are using 1970's tech, then something must be going on with them as of 2014. Or are you saying that most motors out there that are even going into 2014 model boats have been built in 2013 and before? Not trying to give you a hard time, just trying to understand.

If it's the latter....then....

how many Mercs and Volvos come out of the factory as carbureted engines vs EFI's? What's the ratio?

I don't know what it is and I'm only asking because I'm willing to bet it heavily favors motors with EFI. Heavily. So what's the reason for that?

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I think we have succeeded in wandering away from the original question ???????

Can .....ANY OF US.......adjust the idle speed , idle fuel / air ratio..........Put a credit card over a none running lean running engine & motor home if alone & out of radio range for help.

I have been told by boat & auto dealers I have to wait for help. Is that true since 2002 ? That is the only reason I bought a carbed engine. Does any F I system Have a manual bypass system for boats ? I can not step out of the boat & walk to help like a car breakdown.

Hope this gets us back to what I was trying to ask about.

Rich

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I have absolutely noting to add here for the OP (sorry), but this SURE IS an interesting thread!! :popcorn:

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There has never been a 496 to ever roll off the showroom floor with a carb in boats or cars. That is a Vortec truck engine that was released in 2001 and discontinued in 2009 by GM.

True. What happens here is the 496 factory engines get snatched out of the Baha's, Donzi's, etc, and the PCM-555 processors get coupled to the new stroker motor after an injector and fuel pump change out and a ECM re-flash. One of our members actually added a blower to his, but will tell you that was an expensive journey. The factory 496 gets sold as is without the intake. Craig's list is loaded with them but they don't last long, because like you said GM is no longer making them. Merc's new offering is now a World Products aftermarket block with Eldelbrock aluminum heads. It is substantially cheaper to take the transplant approach to a HP upgrade after you factor in the secondary sale of the 496 stock offering. One of the dealers here bought two stock mills up for ready replacements, and some of the upper Chesapeake boys, (3 that I hang with) have bought them as replacements for dead engines, and now they have a roller cam, single piece rear main big block replacement, with stainless steel risers, one of which is a 4 bolt main, steel crank, 496 HO.

You mentioned linear carb output at a given RPM in drag race applications. I raced NHRA modified production in the early 70's and one thing I know for sure. If you are going to stay competitive, then figure on several jet changes and timing adjustments during the course of a single event due to temperature and air density changes. In my case, that meant 8 main jets. If the air change was dramatic, gains were also realized by changing rocker arm ratios. No power valves in these carburetors as all they needed to do was empty a pair of 50 cc accelerator pumps at launch, and with a 3:50 first gear and a 6:50 rear axle ratio, there was not a big issue with bog. Who does that with their boat? Nascar went to injection, and I would have too if the pieces were available and the rules allowed it. Hilborn injection was legal in some classes in drag racing in the 60's, but was expensive and totally mechanical. No incentive for a company to develop ECM based drag race injection when they can get 2 grand for a race ready 1,100 Holley dominator.

I'll stick with my PCM-555 injected 496 HO. 63 MPH, and 3 MPG at 3,150/35 MPH. A 256 SSX is fairly heavy.

W

The 502's and 454's of old with the high CFM factory Rochester Quadrajets suffered from premature intake valve failures. Valve jobs at 600 hours became the norm and fuel injection cured that. I don't know if it was avoiding a lean condition, or less crank case oil contamination that was the cause, but a well maintained 496 that has not been beat will live a good long life. The reciprocating mass is no lighter than it was in the 80's but it does not seem to matter. Better oils I'm sure helped too.

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