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EFI to carbureted

Andy B.

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What are the pros and cons its an 99 502 mpi? I mainly boat at mead with an occasional trip to Havasu.
 

PlanB

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I would never go back to a carb, especially on a boat. All my toys with carbs are a PITA, especially if they sit for a while. Even my brand new Merc's that were carbureted were finicky from day one.
 

240Hallett

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I have a carbureted 1991 454. The small issue I have is first start of the weekend takes a few extra cranks to get fuel up to the carb. My assumption is that the fuel in the carburetor just evaporates from sitting in a hot Havasu garage. After the first start it’s good to go for the weekend.
 

Andy B.

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Depends on what you want to accomplish really , what heads ? what intake is planned ?
Stock heads going to machine shop for some work nothing crazy and not sure on intake the motor has emi thunder exhaust also.

I don't have a lot of knowledge with carburetors do they need tunning every year? Boat sits in my garage from middle of November until late February.
 

Racey

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Stock heads going to machine shop for some work nothing crazy and not sure on intake the motor has emi thunder exhaust also.

I don't have a lot of knowledge with carburetors do they need tunning every year? Boat sits in my garage from middle of November until late February.
Yes, needle and seats, accelerator pumps with the ethanol fuels usually. And set float levels.

I would leave the EFI on it.
 

sonicss31

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I made my 454 Magnum EFI motors to a sorta clone of HP 500’s with a cam change, CMI’s and Edelbrock single planes with 850 Holleys and never regretted it. Just wanted old school maintenance without the need to plug it in to find a bad sensor. To each there own and yes many advised me against it. ;)
 

jetboatperformance

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Stock heads going to machine shop for some work nothing crazy and not sure on intake the motor has emi thunder exhaust also.

I don't have a lot of knowledge with carburetors do they need tunning every year? Boat sits in my garage from middle of November until late February.
Relatively low maintance , actually less to go wrong , tune should stay the same (once done) from on use to the next
 

Bigbore500r

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You can keep the EFI and soup up your 502 MPI.

If your going so far as to have head work done and a camshaft, the biggest thing holding that stock induction setup back is the intake. Get a take-off unit from a 525 that is upgrading to a whipple kit, and you can plop that entire intake / throttle body / injector setup on your motor. I think that intake was developed in partnership with AZ Speed & Marine, i know my Volvo DPX 415 (502) uses the same intake and its an AZ Speed part number. If you go that route, you'll need to have the MEFI ECM tuned, and there will possibly be some changes to harness connectors for the injectors, etc. Another route would be to have the stock Merc intake massaged, some have had success porting them and modifying the runner length inside the intake to increase higher RPM performance (they are a truck intake at heart and really die above 4500). @rvrrat350 had a 540 stroker built out of his 502 MPI, with massaged stock heads, camshaft, and a ported / massaged 502 MPI intake, and it rips
 

Blackmagic94

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Drain the fuel out of the carbs for long term storage. Probably solved. I just fired up the port engine on the cigarette and it started almost instant after not being ran for 16-18 months
 

monkeyswrench

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I like carbs for two reasons, I can work on them, and, to some extent, can afford them. Both FI and carb can be set and pretty much left. Altitude differentials for carbs I try to find a happy medium. Not the most power, but not bad. My jet boat stays at the river, so it's set pretty much accordingly for what it has. The trick from my view is getting the carb setup very close for your end combo, before it is on the motor. As pointed out by blackmagic, draining the carb or carbs for the season will save you a ton of headaches come spring time. At this point in time though, get a parts list together and figure rough cost on everything. Good carbs have become pretty expensive. I'd look at that total, and compare it to other FI intake setups and optional tuning. Weigh your options, no one wants to do it twice.
 

obnoxious001

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There is some chance that you had problems with the EFI and/or fuel pressure based on what I have seen in your engine. If you recall, I told you on the phone before I had met you that you need to have the fuel rail on the odd side (#7 where the main destruction started). That was based on what I have heard about others having similar problems, before I ever knew you had burned a couple of pistons.

I am not necessarily trying to sway you away to a carburetor, but was saying if we built a 540 it could make sense instead of trying to make the Merc injection work with the larger cubic inch engine.
 

Rotten deal

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If your going to a 540, what about Holley fi. lot of people going that route now. Call Boost Power.
 

Shlbyntro

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I honesty vote for carbureted. KISS.

It'll be cheaper to retain the fuel injection and clean it up for the new engine. But the carb is going to be simple, minimal electronics. Just good plain fun. I have never had the reliability issues with carbs that a bunch of these guys talk about. If its set up right, that won't happen. I have had all kinds of reliability issues with fuel injection. Both have their pros and cons, to each their own
 
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ramos45

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If you want to take on the frustrating and satisfying feeling of a properly tuned carb then go for it. I'm in Vegas and can offer some assistance. I'm no expert mechanic but have researched until pinkies go numb (I'm sure some of you know that reference) and have successfully got mine right twice with different blowers.

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Andy B.

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If you want to take on the frustrating and satisfying feeling of a properly tuned carb then go for it. I'm in Vegas and can offer some assistance. I'm no expert mechanic but have researched until pinkies go numb (I'm sure some of you know that reference) and have successfully got mine right twice with different blowers.

View attachment 943829 View attachment 943830
I've seen your boat out by Gator this summer I'm pretty sure it the scarab in your avatar right? Nice boat!
 

Husqy510

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The older EFI found on the 502 and 454 is not failsafe. I've had plenty of friends experience problems from injector issues, to TPS issues and everything in-between. However, when working correctly it's turn-key and safer.

Carbs are simple to work on and shouldn't require any tuning after initial set-up. They are prone to internal and external leaks if they sit a long time, which can be catastrophic if the blower isn't utilized correctly. It would be pretty simple to get over 500hp out of a 502 with a carb, not sure about tuning the older injection.
 

Andy B.

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The older EFI found on the 502 and 454 is not failsafe. I've had plenty of friends experience problems from injector issues, to TPS issues and everything in-between. However, when working correctly it's turn-key and safer.

Carbs are simple to work on and shouldn't require any tuning after initial set-up. They are prone to internal and external leaks if they sit a long time, which can be catastrophic if the blower isn't utilized correctly. It would be pretty simple to get over 500hp out of a 502 with a carb, not sure about tuning the older injection.
No blower nothing crazy just want reliable power.. Barry is taking good care of me.
 

wet hull

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No blower nothing crazy just want reliable power.. Barry is taking good care of me.
If you do go carburetor I have a bunch of great parts listed in parts section. Everything you need as I am going opposite way to fuel injected. Aeromotive pump and regulator, Eddlebrock Air gap and holley 4 barrel carb, billet MSD distributor. All in great condition and ready to bolt onto a standard deck block.
 

Rajobigguy

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I'll just leave this here for you review.
 

ramos45

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I've seen your boat out by Gator this summer I'm pretty sure it the scarab in your avatar right? Nice boat!
I spent some time at the entrance to the bay at the right on the beach during early part of the season. Then, we took it 23 miles to long Beach our last 4 trips out. I like it better out there but it's a good haul
 

zx14

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With efi you’re stuck with finding a tuner, ask me how I know. I’m dead in the water in havasu because no tuner. My idle is a little high. If I had carbs I could fix that. If I had to do over, I would put the largest Cu in bbc with 1 pr 2 carbs and call it a day. At the end of the day, you only need 3 things, air,fuel and spark. I can deal with all 3. Put efi on it, and it took away my ability to work on it. Once the carb is setup, it’s done, end of season, if you have one, put some sty-Bil in the tanks, run it a bit , and your good. If it does gum up, you can take thecarb apart, clean and reassemble, you plug injectors, they are off to somebody to go through and flow test.
Get the carb a good manifold and call it a day. Barry can tune it up for you, set it, and forget it.
 

Boat 405

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I've been down this route. I had a carbed 540 in my 25 daytona. Ran amazing for a couple years. Had someone offer to buy the engine complete and ready to roll. So I sold it. I had a block, crank, and rods and an idea of a big cubic inch EFI deal. I put together a 582 EFI deal and I spent a year trying to get it to run right. Was constantly chasing it with a computer. Had it tuned on the dyno, then again when in the boat. It would still run pig rich. It would start up and idle amazing, just never could get it to run properly and gave up. I have a 2 year old little boy and just don't have the time to constantly mess with it while we want to go boating. I took off the EFI put a brand new holley dominator like I had on the 540 and had it re dynoed. Picked up some hp and now it starts every time and runs amazing. Yes I'd like to go back to EFI some day and learn how to tune it properly myself, but right now I just don't have the time. I spent all the $ doing custom tail pipes with O2 bungs, the Holley EFI setup, 36 skip a tooth crank trigger, the 6 way imco fuel valve with returns, the basically best of the parts plus spares of everything just in case.

End of story, I can tune a carb with my eyes closed, heck I even use the O2 bungs with a standalone O2 monitor to see real time AFR values and can jet up or down, change power valves, or change air bleeds. Sure I could probably do the same with the computer and key strokes, I just do what I know works so I can enjoy boating with my family without drama.
 

Ziggy

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Andy, just get an electric waverunner😁
.
Carb if you're old school and can turn your own wrenches to fix shit. If you're not mechanically inclined regardless of what system(ie. have to get it worked on by others) then do efi and make the boat more user friendly.
.
If all that fails then go plug your E-waverunner while in standing in 3' of water🤪🤣
 

Andy B.

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Andy, just get an electric waverunner😁
.
Carb if you're old school and can turn your own wrenches to fix shit. If you're not mechanically inclined regardless of what system(ie. have to get it worked on by others) then do efi and make the boat more user friendly.
.
If all that fails then go plug your E-waverunner while in standing in 3' of water🤪🤣
I'm ok with a wrench haven't worked on a carburetor since I was 16 and helped my brother rebuild his 428CJ in his 70 mustang. I'm a quick learner im sure I could tune a carb if someone showed me the ropes. Also an excuse to pick up some tools that's always a good thing!

That brought back a good memory thanks I remember when you could work on your own engine without having to plug it into something. Nothing beats wrenching on something with your older brothers those were some of the best times. You dads out there don't take it for granted. My dad passed when I was 3 months old so my older brother was more of a father figure.
 

DaveH

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going from EFI back to a carb is akin to "getting back with an X you already dumped because its easier".

i understand the argument for simplicity.....I really do....and a carb will get you that.

however, EFI will net you better fuel economy, better engine longevity, an overall "happier" running engine and an engine that has many more safeguards and features you simply don't have with a carb.

that being said......IT IS more complicated to setup. The biggest issue i see is people will spend huge sums of $$$ in billet parts....but when it comes to the electronics......they skimp and go with the cheapest junk or factory hacks they can find.

the EFI companies (like Holley) tout "self tuning" and all sorts of other BS trying to dumb down the electronics and installation and only given EFI a bad name.

it is possible to get a good marine EFI system setup. but if you want CHEAP...then stick with a carb.
 

Andy B.

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going from EFI back to a carb is akin to "getting back with an X you already dumped because its easier".

i understand the argument for simplicity.....I really do....and a carb will get you that.

however, EFI will net you better fuel economy, better engine longevity, an overall "happier" running engine and an engine that has many more safeguards and features you simply don't have with a carb.

that being said......IT IS more complicated to setup. The biggest issue i see is people will spend huge sums of $$$ in billet parts....but when it comes to the electronics......they skimp and go with the cheapest junk or factory hacks they can find.

the EFI companies (like Holley) tout "self tuning" and all sorts of other BS trying to dumb down the electronics and installation and only given EFI a bad name.

it is possible to get a good marine EFI system setup. but if you want CHEAP...then stick with a carb.
So what about the original merc efi it did get me to 800 hrs.
 

DaveH

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So what about the original merc efi it did get me to 800 hrs.

here is the problems with your old MEFI system.

1. the software to break into this system is a FUCKING NIGHTMARE to work with. it isn't a real-time tuning platform. its also VERY limited in its capabilities.

2. your old wire harness is probably shot. Most people fail to recognize the ECU takes its input information it gets from sensors/wiring and any issue with the sensors and wiring are usually misunderstood as a "tuning issue" instead of recognizing the intermittent nature of wiring issues.

3. the merc MEFI system is CRUDE. you do realize its TWO CHANNEL fuel? it has no logging capability, no internal wideband 02 capability, limited additional sensor inputs and on and on.

4. the cost of high quality aftermarket systems have come WAY down. but that's just the beginning. most don't recognize what it really takes to properly setup up all aspects of an EFI system, and then blame it on tuning or whatever instead of recognizing its design issues from the start. example......people just install a high pressure fuel pump when they convert to EFI, run some new lines and call it good. the problem is boat fuel tanks don't have any baffles and starvation of the pump when low on fuel or in rough water causes fuel pressure (that don't always show up on a gauge) issues that commonly get blamed on the computer. addressing fuel pressure stability in a boat has nothing to do with the computer but always misdiagnosed as a tuning issue.
 

MK1MOD0

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So here is a question...... has anyone ran a Holley Sniper EFI system on a boat. I know they are self learning, and have great reviews with mild cars engines. I don’t know how aggressive a cam it can accommodate, and how radical a motor will it support.
 

DaveH

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So here is a question...... has anyone ran a Holley Sniper EFI system on a boat. I know they are self learning, and have great reviews with mild cars engines. I don’t know how aggressive a cam it can accommodate, and how radical a motor will it support.
this is the equivalent to an electronically controlled carb. another low budget poor excuse compared to modern EFI.

self learning is BULLSHIT. all it entials is a target mixture table that then takes 02 sensor data and constantly tries to adjust mixture to match the table. the problem is, 02 measurements are not the end all be all and can be highly inaccurate, which in turn makes for a poor running engine.
 

MK1MOD0

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this is the equivalent to an electronically controlled carb. another low budget poor excuse compared to modern EFI.
ok. I get the carb comparison. But ya didn’t answer the question, has anyone ran it on a higher HP boat engine
 

DaveH

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ok. I get the carb comparison. But ya didn’t answer the question, has anyone ran it on a higher HP boat engine
i haven't and while i am sure in the world of the internet there is someone out there doing it......all you have to do is take a look around and you will see it isn't being done for a reason.
 

DaveH

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what is missing in this conversation, is people are not seeing that engine HP output per cubic inch has been going up and up.

this means that precise fuel AND spark delivery are more important than ever. People point to these crude, cheap or outdated systems and say " it worked over here" but fail to recognize it was on a much lower output engine that will tolerate much less accuracy.
 

Shlbyntro

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here is the problems with your old MEFI system.

1. the software to break into this system is a FUCKING NIGHTMARE to work with. it isn't a real-time tuning platform. its also VERY limited in its capabilities.

2. your old wire harness is probably shot. Most people fail to recognize the ECU takes its input information it gets from sensors/wiring and any issue with the sensors and wiring are usually misunderstood as a "tuning issue" instead of recognizing the intermittent nature of wiring issues.

3. the merc MEFI system is CRUDE. you do realize its TWO CHANNEL fuel? it has no logging capability, no internal wideband 02 capability, limited additional sensor inputs and on and on.

4. the cost of high quality aftermarket systems have come WAY down. but that's just the beginning. most don't recognize what it really takes to properly setup up all aspects of an EFI system, and then blame it on tuning or whatever instead of recognizing its design issues from the start. example......people just install a high pressure fuel pump when they convert to EFI, run some new lines and call it good. the problem is boat fuel tanks don't have any baffles and starvation of the pump when low on fuel or in rough water causes fuel pressure (that don't always show up on a gauge) issues that commonly get blamed on the computer. addressing fuel pressure stability in a boat has nothing to do with the computer but always misdiagnosed as a tuning issue.
Funny, sounds like the same thing people like to do with carbs, they never get them set up properly and just blame it on the carb.


ok. I get the carb comparison. But ya didn’t answer the question, has anyone ran it on a higher HP boat engine

I have 1 experience with the sniper efi on a boat. A competitor destroyed a brand new engine in a boat with one (a moderately built big block). He ended up owning the boat, i dont know if the setup was wrong or just a garbage product but I looked at it and didn't like what I saw. I told him to fix it right, we need to take it back to its original configuration with a carburetor. People put too much stock in efi, ot is not the end all be all.

Fwiw I see a lot more high hour carbed engines than I do efi engines. Efi kills marine engine when it goes wrong
 
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DaveH

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Funny, sounds like the same thing peoe like to do with carbs, they never get them set up properly and just blame it on the carb.





I have 1 experience with the sniper efi on a boat. A competitor destroyed a brand new engine in a boat with one (a moderately built big block). He ended up owning the boat, i dont know if the setup was wrong or just a garbage product but I looked at it and didn't like what I saw. I told him to fix it right, we need to take it back to its original configuration with a carburetor. People put too much stock in efi, ot is not the end all be all.

Fwiw I see a lot more high hour carbed engines than I do efi engines. Efi kills marine engine when it goes wrong
if this were the case.....merc and the other manufacturers would still be running carbs.

efi is complicated and the problems i see are due to poor setup and implementation being done by people that shouldn't be doing it because they fall for the snake oil sales pitch of how simple itis.
 

Shlbyntro

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if this were the case.....merc and the other manufacturers would still be running carbs.

efi is complicated and the problems i see are due to poor setup and implementation being done by people that shouldn't be doing it because they fall for the snake oil sales pitch of how simple itis.
the EPA and CARB is what ruined it. Carbureted motors only went away because the cores that they were built out of went away. Reduced availability of carburetor related parts due to the entire ICE industry being forced into fuel injection. It became more cost effective for the marinizers to keep the fuel injection that the engines were coming with from Ford/GM

Although I suspect today with glass cockpits on the rage that they actually would be going out the wayside.
 
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