Hello All! I have a 98 Sundancer 330 with two bad engines. They were both 7.4 MPI's. I will be operating in San Diego Mission Bay (which is salt water) 99% of the time. Very short trips of only a few miles from the slip to cruises around the Bay. Maybe 25-50 miles max on a real long weekend with lots of movement. There will be 1-2 to annual trips to Catalina but above and beyond that it's just going to be in Mission Bay, which is mostly no wake btw. I am considering swapping to Gen IV 454's with carburetors. I have heard both good and bad things about the 7.4 MPIs BUT it seems like they really don't like salt water and I am finding that Gen VI big block parts a hard to find fast and cheap and I need fast at the moment. I do all my own work and I can definitely go through the existing EFI systems and get them going again but I would HATE to spend all that time and money to have constant issues. Having a strong hunch towards going with the old Thunderbolt ignition system and some simple Edelbrock carburetors. I know EFI is safer on an inboard but I am pretty meticulous about maintenance and I keep my eyes on things. Am I crazy for wanting to go old school?
Thoughts on going from 7.4 MPI Gen VI to Carb Gen IV
- Thread starter grod1987
- Start date
techmitch
Well-Known Member
- May 1, 2008
- 8,423
- Boat Info
- 1999 270 DA
- Engines
- Twin 4.3s W/Alpa I Gen II's
Your not crazy, but I wouldn't do it.
boatrboy
Well-Known Member
I'll second that. I had 600 hrs. on mine with no trouble but I realize one man's opinion doesn't constitute fact.
I have friends who always complaining they are replacing carb's because the don't idle or run cold, or ethanol gas ruined them etc.
Look at the pros and cons of both.
I loved that I never needed to touch a choke. My MPI just started and ran. I'm sure if carbs were more reliable, Mercruiser and Vovlo would have them on every motor. Sure the rebuilt small blocks come with carbs, but that is the minority.
I'm sure there will be a lot of opinions coming...
BTW - Welcome to Clubsearay.
techmitch
Well-Known Member
- May 1, 2008
- 8,423
- Boat Info
- 1999 270 DA
- Engines
- Twin 4.3s W/Alpa I Gen II's
How long you gonna keep her?... https://searay340restoration.blogspot.com/
Carbs can definitely be touchy. I think a lot of their issues can be traced back to user error though. I have torn through countless marine carburetors and had to fix what the previous ‘mechanic’ did. I have been playing with carbs since I was a preteen so troubleshooting them is 2nd nature to me.
Ethanol fuels aren’t nice to carbs. You need to keep them dry during the off season. That’s the secret to longevity. The way I see it I can keep a spare carb on the boat along with a distributor, alternator, water pump, raw water pump, hoses, tune up parts, etc to make easy on the water swaps as needed. Hard to do that with EFI but the engine room is definitely large enough.
Ethanol fuels aren’t nice to carbs. You need to keep them dry during the off season. That’s the secret to longevity. The way I see it I can keep a spare carb on the boat along with a distributor, alternator, water pump, raw water pump, hoses, tune up parts, etc to make easy on the water swaps as needed. Hard to do that with EFI but the engine room is definitely large enough.
Long time
- Apr 26, 2009
- 5,821
- Boat Info
- '97 330 Sundancer, Raymarine C80 suite with radar, Mercury 310 Hypalon w/8hp Yammie 2stk
- Engines
- 2X 454 carbs w/ vDrives
My 97 330 has the original carbs. No problems for me. The bowls do leak down dry after week or so of non use. But it just means about 5 seconds of crank for the mechanical pumps to fill the bowls. If it’s been only a couple of days they fire right up. When I shopped for mine I was indifferent to carb vs MPI. Others may differ in view on resale.
Chris-380
Well-Known Member
I once had a friend that said “I bought the carbs instead of efi because I can work on them”
We joked about 5-6 years later when he was struggling with them and we said “there, now you have to work on them!”
I love my mpi motors, nothing against carbs, but they are pretty maint free and start pretty much every time
We joked about 5-6 years later when he was struggling with them and we said “there, now you have to work on them!”
I love my mpi motors, nothing against carbs, but they are pretty maint free and start pretty much every time
Stee6043
Well-Known Member
1,300 hours on my MPI's. I fully expect another 1,300.
Carbs are for old people that still believe the internet is just a fad
Carbs are for old people that still believe the internet is just a fad
Skybolt
Well-Known Member
- Nov 11, 2014
- 6,487
- Boat Info
- Reel Nauti
460 EC
- Engines
- Detroit 6v92TA
(Low profile's)
Alison Gears
Westerbeke
12.5kw Genset
Nothing wrong with Quadrajets, they do develop cracks at the stem and the bowls leak down after a few days. But it's an internal leak and doesn't hurt performance.
Carb vs FI, FI will use less fuel. A 340 with carbs will burn ~36-8 gal/hr at cruise and FI ~6-8 gal less. But YMMV...
Carb vs FI, FI will use less fuel. A 340 with carbs will burn ~36-8 gal/hr at cruise and FI ~6-8 gal less. But YMMV...
John E3
Active Member
Gen 6 parts are not hard to find, there is a new version of them readily available. I bought new heads last year, available from tons of places, and I also looked at new shortblocks, too. Beware, there are 2 versions, 3/8" or 7/16" mounting holes for all the fore and aft bolt on accessories. My Horizons are 7/16. If you are looking for original engines, good luck, they have pretty much dried up due to popularity, and time since last made. I looked for rebuilt heads (mine were beyond repair) and found very little, new was only slightly more. On rebuilds, if the block mating surface on the heads were milled you need to change the pushrods as they are non-adjustable (may be Horizon specific). Cheap is not an available option that I found.
Mercruiser specific parts could be a different issue, but normal wear stuff is readily available. I would think the MEFI (1, 2, 3, etc) may be the most difficult item to source. It looks like there may be aftermarket versions.
Regarding saltwater, are yours not FW cooled?
Mine fired up on the first try after sitting since November. The same was true after I rebuilt the one last year. Static set the distributor, bled the air from the fuel rail, and on the first crank it fired off and startled me as I did not expect it to! My last carbureted engines (1962 Chris Craft 283's) never started on the first try, when cold. They were 100% rebuilt, including professional rebuilds on the Rochester 4GCs. Not sure these are a fair comparison!
I do have ethanol free gas in mine currently, so that probably helps.
PlayDate
Well-Known Member
Carb guy here. I work on both EFI and Carbs.
I appreciate your question. We have had several threads that seem to go on forever trying to sort out MPI/EFI issues. Let me recap the problem areas:
-Cool Fuel interior flaking
-Injectors getting clogged
-Sensors
-ECUs
-Throttle Bodies
-Need for diagnostic app or device
There are a lot of things that MPI/EFI systems do well but when they experience issues.....they are very expensive to resolve.
The advantage that you have is that you are not trying to put a carb on an MPI/EFI engine. That creates a level of problems you don't want. Starting with a Gen IV setup makes it easy. The only real issue is the engine connector and having a lot of extra harness wires which are no longer needed.
I like using a low pressure electric fuel pump over the mechanical pump because it gives you the equivalent of turn key starting. Holley makes an oil pressure cut off switch to ensure it meets USCG requirements.
As to the carb.....that is always a personal preference. I have used marine grade Holleys forever and frankly have none of the problems cited by my colleagues. Holleys don't leak down and they are easy to tune.
It is up to you but I would consider doing it just because your existing EFI system is 26 years old. You will be chasing EFI gremlins at best.....at worst.....the engines won't run.
Just my opinion. I have a few other recommendations if you decide to go down the carb path.
Alternatively......I also like the Marine Holley Sniper EFI systems. They are easy to install and maintain. They are a throttle body injection system which gives you the simplicity of a carb with a tunable EFI system. The only downside is having to use the existing high pressure fuel pump.
I appreciate your question. We have had several threads that seem to go on forever trying to sort out MPI/EFI issues. Let me recap the problem areas:
-Cool Fuel interior flaking
-Injectors getting clogged
-Sensors
-ECUs
-Throttle Bodies
-Need for diagnostic app or device
There are a lot of things that MPI/EFI systems do well but when they experience issues.....they are very expensive to resolve.
The advantage that you have is that you are not trying to put a carb on an MPI/EFI engine. That creates a level of problems you don't want. Starting with a Gen IV setup makes it easy. The only real issue is the engine connector and having a lot of extra harness wires which are no longer needed.
I like using a low pressure electric fuel pump over the mechanical pump because it gives you the equivalent of turn key starting. Holley makes an oil pressure cut off switch to ensure it meets USCG requirements.
As to the carb.....that is always a personal preference. I have used marine grade Holleys forever and frankly have none of the problems cited by my colleagues. Holleys don't leak down and they are easy to tune.
It is up to you but I would consider doing it just because your existing EFI system is 26 years old. You will be chasing EFI gremlins at best.....at worst.....the engines won't run.
Just my opinion. I have a few other recommendations if you decide to go down the carb path.
Alternatively......I also like the Marine Holley Sniper EFI systems. They are easy to install and maintain. They are a throttle body injection system which gives you the simplicity of a carb with a tunable EFI system. The only downside is having to use the existing high pressure fuel pump.
Different engine, similar scenario.
I had a 1998 2 stroke Evinrude outboard with a carb. It was all mechanical and I learned how to fix everything on it. Rebuild the carb a bunch of times, and did the required in-water tuning. I liked it because it was simple and I could do the repairs myself.
But then I got really tired of having to do the repairs myself. Constantly adjusting the idle and linkages, cleaning and rebuilding the carb from the ethanol, idling issues. So I sold it and got a Mercury 4stroke EFI outboard. It requires a computer to do diagnostics, but all the frequent adjustment issues are gone. Maintenance is simplified (except having to change the oil. I do miss the ability to be 100% independent on the repairs, but the operations trade off is in my favor.
I had a 1998 2 stroke Evinrude outboard with a carb. It was all mechanical and I learned how to fix everything on it. Rebuild the carb a bunch of times, and did the required in-water tuning. I liked it because it was simple and I could do the repairs myself.
But then I got really tired of having to do the repairs myself. Constantly adjusting the idle and linkages, cleaning and rebuilding the carb from the ethanol, idling issues. So I sold it and got a Mercury 4stroke EFI outboard. It requires a computer to do diagnostics, but all the frequent adjustment issues are gone. Maintenance is simplified (except having to change the oil. I do miss the ability to be 100% independent on the repairs, but the operations trade off is in my favor.
Being crazy and not doing something are not necessarily mutually exclusive. Personally I would never go back to carbs. It's not like FI is a new untested technology. It's just not old-old-old school.
- Apr 26, 2009
- 5,821
- Boat Info
- '97 330 Sundancer, Raymarine C80 suite with radar, Mercury 310 Hypalon w/8hp Yammie 2stk
- Engines
- 2X 454 carbs w/ vDrives
When it’s time for a major rebuild on my carbs I will sell them and install Holley marine carbs. I have heard nothing but good things about them.
No not crazy. To me it is a matter of personal preference. If you can rebuild a carb effectively it has the inherent advantage of being able to be fixed with a $50 carb kit and simple hand tools.
When I repowered my boat in 2015 I went the carb route for that reason. We boat on a northern lake so the season is too short if you have an issue to wait on parts or marina. I can be pretty self sufficient by keeping carb kit, spare ignition sensor and module for the Thunderbolt.
Certainly nothing wrong with MPI, not going to bad mouth it. For my style of boating- older boat, do my own maintenance, try to keep costs reasonable its a better fit. Any of the carbs properly set up be it Q-jet, Holley, or Edelbrock will work fine if you dont mind setting the choke before starting....
PlayDate
Well-Known Member
Interesting you mention the choke.
18 years ago when I put the Holleys on my engines......I splurged and spent $50 a piece for the electric choke control.
Honestly......it was a waste of money for at least my boat (I electrically disconnected them and rotated the choke position to full open). It never really gets cold enough in the mid Atlantic where the start up needs a choke to start them. On a cold start usually two pumps on the throttle .....and they start right up. I don't leave the slip until the engines warm up so a choke doesn't add a lot of value at least in my application.
I could see if you needed to get underway quickly where they would be helpful. On warm restarts......you definitely do not need a choke or to pump the throttle.
You are correct generally not needed for warm weather and hot restarts. Just mention it because it is the big 'advantage' folks mention in favor of fuel injection, turn key starts. The edlebrocks like 1409 I run has a habit of dribbling fuel after shutoff so end up opening the throttle some to clear and overly rich condition. They make an insulating thick gasket that helps with this.
I ran my old boat for years with out choke when the element died. Did the same thing just adjusted so lean it never closed...
only had an issue when taking it out in October (upstate NY) cold wet and rainy mornings really had to get warm.
Again I think it is personal preference and mechanical comfort level.
Scott215
Well-Known Member
- Jun 4, 2022
- 2,243
- Boat Info
- 2006 215 weekender 5.0 mpi
- Engines
- 5.0 mpi alpha 1 gen 2
I thought the newer blocks don't have the fuel pump boss on the block. I would stick with efi . Easy to diagnose and find parts for. Don't like thunder volt at all. Lots of issues I've heard
AS EFI systems age they become problematic. The MPI's don't tolerate wear in throttle shafts well and what that play does to that fragile calibration. Their ECM's are bulletproof though.
Half the battle in Mercruiser EFI is finding a mechanic that knows what they are doing not only to diagnose, but repair and calibrate. It seems by reading posts here that "mechanics" throw snot on the wall hoping something sticks and consequently the massive cost associated with their work. On the other hand getting a carburetor to calibrate for use isn't plug and play either and finding someone do do that is getting rare. Sure they run bolted on but they still require jetting, idle mixture setting, power valves (Holley), throttle blade set for fuel transition, etc. I'm with @PlayDate on the Holley fuel injection especially if you are going to hang onto the boat. But, here we are again needing expertise getting the system set up correctly even though it is so much more sophisticated in the data on common laptop computers and the ability to get it tuned and trimmed.
Assuming you're not a sick motorhead (like me), I'd stay with the Mercruiser system but get a qualified mechanic to get it right.
Half the battle in Mercruiser EFI is finding a mechanic that knows what they are doing not only to diagnose, but repair and calibrate. It seems by reading posts here that "mechanics" throw snot on the wall hoping something sticks and consequently the massive cost associated with their work. On the other hand getting a carburetor to calibrate for use isn't plug and play either and finding someone do do that is getting rare. Sure they run bolted on but they still require jetting, idle mixture setting, power valves (Holley), throttle blade set for fuel transition, etc. I'm with @PlayDate on the Holley fuel injection especially if you are going to hang onto the boat. But, here we are again needing expertise getting the system set up correctly even though it is so much more sophisticated in the data on common laptop computers and the ability to get it tuned and trimmed.
Assuming you're not a sick motorhead (like me), I'd stay with the Mercruiser system but get a qualified mechanic to get it right.
