How do I convert my carburated 351 to fuel injection?

[kyancy]

Hello all my "2001" nautique lovers! Im thinking about converting my 84 stock 351 to fuel injection. How big of a pain is this process and where do I start? Is it as simple as the manifold, injectors, and air assembly? Does it require some sort of OEM computer or something? What would a ballpark figure for the parts run me? Any info or opinions would be very much appreciated!!!

Thank You

KYancy

[Mikeski]

Why? The carbed 351 is a great running motor. When tuned correctly it will start with 2 throttle pumps from dead cold and with a quick turn of the key otherwise. If you want more power you could add some GT40 heads but I would keep the carb. As boats age I really prefer the simplicity of a carb.

[Nautiquehunter]

This topic has been discussed before you can use the search box to get that info. As I recall its not cost efficient . There are a number of systems available the cost is around 1500.00 and up .

[east tx skier]

Step 1. Unscrew throttle knob.
Step 2. Sell Boat.
Step 3. Buy newer fuel injected boat.
Step 4. Replace throttle knob on new boat with knob from old boat.

I think Holley sells a throttle body injection system kit that would work. But I'll still vote for keep the carb.

[TX-Foilhead]

Don't bother with the Holley system, I've never heard anyone say they have one that works. It the Hp these boats develop are at the very upper range of what the Holley can handle. There was someone on CCF who put a Powerjection III system on last summer, he claimed it worked great. After looking into it looks like its about $2000. Really the only improvement over a carb would be easy starts year round, shouldn't be much if any fuel savings with a throttle body system.

[swc5150]

Agreed... if your carb is well maintained, you won't notice much of a difference with TBI EFI. I do understand what you're saying though. If it's an easy/inexpensive swap, why not... but it's not.

[TRBenj]

Gotta agree with East TX Skier! The most straightforward (not to mention cost effective) way to convert to fuel injection is to buy a boat that already has it. The conversion will be difficult and expensive. If youre very mechanical, like to tinker, have lots of extra money laying around, and are not afraid of having a non-functional boat for a good long while as you get it to work properly, then go for it!

Many consider this type of project, a few actually try it... and I know of maybe 2 that have successfully finished it. Not for the faint of heart!

[Mamigacz]

I am very interested in this myself. My manifolds are removed right now. I am going to bring one to the machine shop and rework a spot on it to accept an O2 sensor. Im not sure when I going to pull the trigger on the full conversion, but I wanted to start with the O2 modification and maybe the fuel return line to the gas tank. Even if I don't do the efi conversion, I wanted to find out if im running rich or lean. Those wide band guages are nice for fine tuning carberators.

[DanielC]

The way I would do this is three simple steps.
1. Find a marine fuel injected GT-40 engine that is running.
2. Remove the carburetor 351 in the boat.
3. Put the fuel injected 351 in it's place.

[rman56]

A friend of mine has a 34 Ford with a 351 in it and he changed it over. He used a FAST set up and works really well but not sure how it would work in a marine application. I have talked to them about it last year but have not decided yet.

[Mamigacz]

Fast EFI is thesystem that I'm interested in. The three big things that need to be converted are:

-(1) exhaust manifold or riser needs to be able to accept a wide band O2 sensor. I’m in the process of doing this right now.
-The gas tank has to be modified to accept a low pressure fuel return line.
-The mechanical fuel pump is replaced with a high pressure electric fuel pump. This fuel pump comes with the FAST EFI kit.

FAST EFI costs about $1800 (not cheap). I have not found anything yet that says its marine safe. However, I did find some videos on YouTube of guys with I/O's that converted there carbureted boats into EFI with the FAST EFI system. The cool thing about it is that it tunes itself the more you use it. I don’t think it’s going to give much of a performance increase. I might give a slight decrease in fuel consumption. I would hope it would help with easier starts, lower RPM idling, and smoother accelerations.

The thing that irritates me about my carbureted set up is that on hot days I get an issue where the boat doesn’t want to start immediately after it sits more than five minutes. I think the gas is evaporating in the carburetor bowl causing starting issues. I have tried a phenolic spacer, heat shield, gas without ethanol (this did help a little) and a different coil. Nothing keeps it from happening. My previous boat also had a 351W carbureted engine and it did the same thing onhot days. I know how to get it restarted, but my wife can’t.

[TRBenj]

The thing that irritates me about my carbureted set up is that on hot days I get an issue where the boat doesn’t want to start immediately after it sits more than five minutes. I think the gas is evaporating in the carburetor bowl causing starting issues. I have tried a phenolic spacer, heat shield, gas without ethanol (this did help a little) and a different coil. Nothing keeps it from happening. My previous boat also had a 351W carbureted engine and it did the same thing onhot days. I know how to get it restarted, but my wife can’t.

I disagree on your assessment. That is not how a properly tuned carburetor should act. I would put a little more effort into troubleshooting the issue properly before springing for an expensive, unproven, and potentially dangerous EFI retrofit.

[Mamigacz]

I called FAST today, they said FAST EFI it is marine safe. The only difference is some parameter changes due to the low thermostat temperatures. The rep said they have sold many systems for marine applications. I agree it is expensive. I'm not ready to fully pull the trigger on this conversion, but it looks very interesting.

I'm open for any suggestions for tuning. My boat runs extremely smooth at idle (600RPM in gear), excellerates without any stumbles or misses, holds a steady RPM when cruising, starts immediately when the weather is below 80 (engine hot or cold). It runs like its jetted properly. Fuel pressure is at 5 psi. Needles and seats were replaced two years ago. What are some tuning suggestions to keep it from starting hard when its hot out?

[TRBenj]

Gotta figure out what the problem is first. I have my doubts that ambient temps have anything to do with it... it doesnt get that hot in Wisconsin! What do you have to do to make it start when it acts up? Have you tried looking down the carb throat to see if its dripping after shut down? 9 times out of 10, it is, when the boat acts as you describe. Could be a bad needle/seat, a bad casting on the bowl, or schmeg stuck in there. I would be more suspicious of it just because it was replaced 2 years ago... very common problem, especially with new parts.

The other thing to do is feel the coil when it doesnt want to start... if its really hot, it could be on its way out. This, combined with a no spark condition would point to it as the culprit... but I would expect it to act up once the boat is warm, even when the ambient temps are cool.

[Puzzlescort]

on one of our ford cars we had a similiar problem with it playing up when hot & it would not start again till cooled down...

to cut a long story short after chasing & replacing so many parts the problem ended up being was the wire mesh strainer on the fuel inlet into the carby - only something else to look at