Converting to carburetor from mpi 350 mag

[Ignatios]

Edelbrock has Marine Manifolds for the SB Chevy
Holley has several Carbs that will work. My preference is the 650 Spreadbore.
I don't know if the Ignition Advance is provided by the ECMs which are fried, or is Independent. You might have to get a Distributor that has it's own advance.

Ignition is independent.

 

[ROY WILLIAMS]

Boat was on rack hooked to a land power.

so the boat was on a power cord ? the lightning hit the power lines ...
last week I had the electrical power lines on the street hit the lightning .. my house shut down the electrical around 30 min ..
I install the electrical surge protector ....

 

[Ignatios]

so the boat was on a power cord ? the lightning hit the power lines ...
last week I had the electrical power lines on the street hit the lightning .. my house shut down the electrical around 30 min ..
I install the electrical surge protector ....

There had to be some failure somewheres or who knows it might’ve hit the boat directly.

 

[Ignatios]

Maybe try giving this place a call just to see if maybe they can help fix, sell you or buy your old ECM if you do go carbureted, https://marineecm.com/

Maybe upgrade to MEFI 4

MEFI SERIES REPLACEMENT ECMS WITH TUNE OF CHOICE – BOOSTPOWER USA

Look up Merc part 865962A02 CARBURETOR TKS RETROFIT KIT for an example. https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2047675.m570.l1313&_nkw=865962A02&_sacat=0

​

I tried to stay ECM but it was tough to find the same or even upgrade to mefi4 and it is very costly but even if I did I may find out that I have to change yet the sensors and then pay some to use their gadget to tune in everything, thus I went with the carburetor however now I still got to solve the harnesses issue.
The boat now cranks all gages are up the only thing is no power to the fuel pump and the coil pack cup… so was wondering if I need special harness for that or maybe can get away with the same one?
Any thoughts
Have a blessed Sunday.

 

[Lou C]

That’s a good question actually for anyone who wants to convert. You need a low pressure fuel pump & the unit you have for EFI won’t work unless there’s a way to just use the low pressure pump separately (carb needs only 4-6 psi fuel pressure vs EFI much higher). So you probably need to buy a Carter low pressure electric pump with the safety harness hooked up to an oil pressure switch. What you’re going to do is just replicate Merc’s earlier electric pump set up for carbs. Several in here have listed up how to do it (Rick Stephens). Now for the distributor you may need to use a stand alone unit like the Delco EST.

 

[Lou C]

Also you are going to need some parts to make the throttle hookup which you can find on Holley’s website

 

[stresspoint]

the reason you should not use the HP fuel pump is the carb has no return line or fuel pressure regulator to send unused fuel back to the tank .
relying on a simple needle and seat to hold 18 or more PSI of fuel pressure is asking for trouble / leak.
a holley carb has no option for a return line , holley makes an adjustable regulator that will allow you to use a high pressure pump but i think the cost will exceed that of a OEM low pressure pump.

 

[Ignatios]

Also you are going to need some parts to make the throttle hookup which you can find on Holley’s website

Thanks for the site I will definitely be using it.

 

[Ignatios]

the reason you should not use the HP fuel pump is the carb has no return line or fuel pressure regulator to send unused fuel back to the tank .
relying on a simple needle and seat to hold 18 or more PSI of fuel pressure is asking for trouble / leak.
a holley carb has no option for a return line , holley makes an adjustable regulator that will allow you to use a high pressure pump but i think the cost will exceed that of a OEM low pressure pump.

Using a low pressure regulator after fuel pump. Any thoughts?.

 

[Ignatios]

the reason you should not use the HP fuel pump is the carb has no return line or fuel pressure regulator to send unused fuel back to the tank .
relying on a simple needle and seat to hold 18 or more PSI of fuel pressure is asking for trouble / leak.
a holley carb has no option for a return line , holley makes an adjustable regulator that will allow you to use a high pressure pump but i think the cost will exceed that of a OEM low pressure pump.

I got one from JEG I was told I don’t need new pump or do anything except to install this low pressure regulator

 

[Scott Danforth]

I would swap out the high pressure pump for a low pressure pump myself

Without ECM, you will need to wire the fuel pump to prime off of starter and get power thru oil pressure switch

 

[Lou C]

Agreed that’s what I thought worries about depending on a regulator to not overpower the carb

 

[Scott Danforth]

Good news is there is a Carter low pressure pump that will directly interchange with the high pressure

 

[Ignatios]

Ok after so long I am not sure what is going on… I am not getting spark out of the coil.
When I turn the switch on all gages comes on except the water temp because it is not connected yet… I have a power line to the coil positive and then it Continue to the fuel pump, the fuel pump comes on when I turn the key switch on, now this power line is coming from the harness, I ran a line from the negative on the coil to the distributor white/red line, I left the white/green line in the distributor not connected for now, I believe it runs to the tach, and the black line negative again from the distributor to the engine block.
Now power to the coil positive is good(13+) coming out of the negative on the coil to the distributor (white/red) is good 13+, coming out of the white/green line is good it seems like tach line because i get intermediate power out of it, the problem is I’m not getting spark from the secondary coil to the distributor I tested the coil for primary and secondary it is good, but still got a new coil tried it, got the same thing no spark coming out of the coil, I replaced the sensor in the distributor (thunderbolt V or IV) changed the cap the rotor still nothing.
Any thoughts what could it be?
Thank you very much and God bless.

 

[Ignatios]

Ok after so long I am not sure what is going on… I am not getting spark out of the coil.
When I turn the switch on all gages comes on except the water temp because it is not connected yet… I have a power line to the coil positive and then it Continue to the fuel pump, the fuel pump comes on when I turn the key switch on, now this power line is coming from the harness, I ran a line from the negative on the coil to the distributor white/red line, I left the white/green line in the distributor not connected for now, I believe it runs to the tach, and the black line negative again from the distributor to the engine block.
Now power to the coil positive is good(13+) coming out of the negative on the coil to the distributor (white/red) is good 13+, coming out of the white/green line is good it seems like tach line because i get intermediate power out of it, the problem is I’m not getting spark from the secondary coil to the distributor I tested the coil for primary and secondary it is good, but still got a new coil tried it, got the same thing no spark coming out of the coil, I replaced the sensor in the distributor (thunderbolt V or IV) changed the cap the rotor still nothing.
Any thoughts what could it be?
Thank you very much and God bless.

Just as a reminder, ECM is out harness is out intake been replaced with a carbureted intake and a quick fuel technology carburetor the only thing that left is the knock sensor using the same oil and water temp sensors… did I miss something ?

 

[Scott Danforth]

Tach wire is gray

 

[Ignatios]

Tach wire is gray

So what is the white/green?

 

[Scott06]

So what is the white/green?

Goes between ignition module and dist on tb ignitions not dist and coil

whats your engine number

 

[Ignatios]

Goes between ignition module and dist on tb ignitions not dist and coil

whats your engine number

serial number L365398
I converted to carburetor from mpi after my computer got toasted with a lightning.

 

[Ignatios]

All I have is distributor and old style coil cup, 3 wires coming out of the distributor white/red white/green and black those are actually coming out of the a sensor that is seated inside the distributor