Adding TBI

[shrfdeputy]

My 1995 252 has the 7.4 GL which means a big, thirsty 4 barrel carburetor. Honestly it was the only thing that scared me a little when I first bought the boat. After adding about 120 hours on the clock I can say the fear was largely unwarranted. The boat usually starts just fine with a little pump of the throttle before cranking. I keep good gas in it and change the spark plugs about every 50 hours.

Since we added the swim platform and captain's call there has been a bunch of soot that is constantly on the transom. I've followed some posts on here and kept the fuel at 89 octane (what it calls for) as much as possible, but many times my only non-ethanol option is 91. I've talked to my mechanic and he says the carb'd boats were set up to run a little rich from the factory. Volvo Penta did not want a trip to Tahoe or some other high-altitude lake to result in a leaned out condition that could lead to serious engine damage. Basically he has told me it may be time to rebuild the carb or change power valves at the least, but he does not think I should be concerned about it.

On this last trip to Table Rock I could tell the carb was putting out more fuel than the engine could burn at idle. There was a little fuel in the water behind me if I fired it up and just sat there. Each year I've had the boat we have done some sort of upgrade to make the boat more enjoyable for us over the winter/early spring. I'm thinking this off-season I need to address this. My fuel burn is a tiny bit over 1 mpg, so a blast across 1/3 of Table Rock REALLY runs through some dead dinosaurs in a big hurry.

Here's my question: Has anyone switched to a TBI on an older boat like this? I'd be interested in hearing all opinions, but specifically regarding a 7.4 Volvo Penta. It looks like I can get a "turn key" system for about $1,200-$1,500 online that appears to come with everything I would need. I know I could expect better starting, and maybe a little better fuel economy, but I don't want to sacrifice power. I think any of you who have run beside my 252 at the Regatta or otherwise can attest to the fact that it performs better than you would expect a base 7.4 from 1995 to run, so I don't want to lose that. Would TBI keep or maintain the current power level? Is the cost and initial installation headache worth it? Would I be better off to rebuild and tune the current carb, or would a new carb be a third (and better) option. I'm looking for reliability, easy starting, no loss of power, and (less important) better fuel mileage.

[cmattj]

As calibration for efi is enriched for the marine lugging engine environment you have a task ahead. When I researched my 97 7.4 Sea Ray to convert I found ecu conflicts along with high pressure fuel systems helped me loose interest. There are some stand only aftermarket companies now that seem to have it figured out but those mid years are tricky. As they still have ecu ignitions that need to be delt with. Car systems are easy with o2 and tuning abilities but boats with wet exhaust mean your going to have to trust the system you purchase.
Don’t be to afraid to dial the carburetor as carter/ edlebrock both make series for marine calibration, and the idle mixture can be leaned down to almost stalling in gear. While still providing enriched cruise speed to avoid pinging.
Just a thought

[shrfdeputy]

As calibration for efi is enriched for the marine lugging engine environment you have a task ahead. When I researched my 97 7.4 Sea Ray to convert I found ecu conflicts along with high pressure fuel systems helped me loose interest. There are some stand only aftermarket companies now that seem to have it figured out but those mid years are tricky. As they still have ecu ignitions that need to be delt with. Car systems are easy with o2 and tuning abilities but boats with wet exhaust mean your going to have to trust the system you purchase.
Don’t be to afraid to dial the carburetor as carter/ edlebrock both make series for marine calibration, and the idle mixture can be leaned down to almost stalling in gear. While still providing enriched cruise speed to avoid pinging.
Just a thought

I definitely don't want to get into something that is harder to deal with than what I have now. I DID however find one this morning in a quick internet search that claims to have water proof oxygen sensors that would tend to be easier to tune. It required removal of the riser to drill a hole in a specific spot. It was a mercruiser application though so I would still be flying blind if I tried to use it.

[Big Block Power]

Sorry but carbs to me have been a nightmare forever. Your not going to change that. Get it rebuilt. They will always be rich to a point. Myself I said a few years ago I would never buy another carb boat in my life.

[AsLan7]

Sorry but carbs to me have been a nightmare forever. Your not going to change that. Get it rebuilt. They will always be rich to a point. Myself I said a few years ago I would never buy another carb boat in my life.

.
+1

[akorcovelos]

I agree with BB, but converting a carb boat to FI generally isn’t worth it, and if you do, don’t try and do a closed loop system with o2 sensors, get a simple open loop system like the same vintage mercury engines had, that way you just need a good base tune. That said, I think it would be far easier and cheaper to have the carb rebuilt and tuned with a remote AFR gauge in the exhaust.

[Ytmsn]

As calibration for efi is enriched for the marine lugging engine environment you have a task ahead. When I researched my 97 7.4 Sea Ray to convert I found ecu conflicts along with high pressure fuel systems helped me loose interest. There are some stand only aftermarket companies now that seem to have it figured out but those mid years are tricky. As they still have ecu ignitions that need to be delt with. Car systems are easy with o2 and tuning abilities but boats with wet exhaust mean your going to have to trust the system you purchase.
Don’t be to afraid to dial the carburetor as carter/ edlebrock both make series for marine calibration, and the idle mixture can be leaned down to almost stalling in gear. While still providing enriched cruise speed to avoid pinging.
Just a thought

Matt I'm just curious, what would happen if he dropped a Holley in there and tuned it for his motor? And what would you go with?

Here is a link

https://www.holley.com/products/marine_ ... rburetors/

[cmattj]

Holley Carbs are great!
Most had Holley marine carbs of that Volvo era. I assumed it was a Holley as he mentioned “ power valve “ which only Holley has.
Not to be a Debbie downer but most owners don’t know that a quick backfire on start up can pop the diaphragm, and result in a rich idle.
( Most people don’t know how to change them so they become a unknown rich condition).
My suggestion of Carter Afb or a edlebrock was for they have a different idle circuit design, thus require no maintenance.
But I’m a Holley guy as you can tune them in more capacity.

[shrfdeputy]

Holley Carbs are great!
Most had Holley marine carbs of that Volvo era. I assumed it was a Holley as he mentioned “ power valve “ which only Holley has.
Not to be a Debbie downer but most owners don’t know that a quick backfire on start up can pop the diaphragm, and result in a rich idle.
( Most people don’t know how to change them so they become a unknown rich condition).
My suggestion of Carter Afb or a edlebrock was for they have a different idle circuit design, thus require no maintenance.
But I’m a Holley guy as you can tune them in more capacity.

I appreciate the responses. I did forget to say the boat has the original Holley carb on it still.

It's funny that you mention a backfire. I have things rolling in my mind now. Last year right around July 4th we had a backfire issue that popped up. It was never on start up, but under a load while the boat was getting on plane. It usually happened around 2800-3000 rpm. I chased that for a few weeks until I finally figured out the flame arrestor was badly clogged. I cleaned it out and the boat ran perfectly.

Interestingly enough I never really noticed any soot on the transom until about that time. I assumed it was from running the captain's call and having the air trapped by the new swim platform. So now I've about got myself convinced I damaged the power valve when we had the backfire issues last year. I even remember reading that a bad power valve may cause a sooty transom. Sounds like I need to see about changing it. Hopefully youtube can be my friend yet again.

[Lockey14s]

The black around the transom is very common when you have thru hull exhaust, constantly have to clean it. You have a good carb on it being holley. I would get it deep cleaned and rebuilt. i bet your fuel consumption will go down and you will get close to what a fuel injected setup would get. in my opinion, dont mess with changing to FI, not worth it.

[shrfdeputy]

The black around the transom is very common when you have thru hull exhaust, constantly have to clean it. You have a good carb on it being holley. I would get it deep cleaned and rebuilt. i bet your fuel consumption will go down and you will get close to what a fuel injected setup would get. in my opinion, dont mess with changing to FI, not worth it.

Thanks Steve. I think I'm convinced staying with what I have is the way to go.

[Lockey14s]

The black around the transom is very common when you have thru hull exhaust, constantly have to clean it. You have a good carb on it being holley. I would get it deep cleaned and rebuilt. i bet your fuel consumption will go down and you will get close to what a fuel injected setup would get. in my opinion, dont mess with changing to FI, not worth it.

Thanks Steve. I think I'm convinced staying with what I have is the way to go.

No Prob! I would get it cleaned and rebuilt and run it next year. if you are still unhappy or want to improve it then go from there. To be honest, its probably easier and less work to find a drop in fuel injected motor and swap it out rather than try and convert yours over. And if you go this route you might as well upgrade to a 496... just sayin

[shrfdeputy]

The black around the transom is very common when you have thru hull exhaust, constantly have to clean it. You have a good carb on it being holley. I would get it deep cleaned and rebuilt. i bet your fuel consumption will go down and you will get close to what a fuel injected setup would get. in my opinion, dont mess with changing to FI, not worth it.

Thanks Steve. I think I'm convinced staying with what I have is the way to go.

No Prob! I would get it cleaned and rebuilt and run it next year. if you are still unhappy or want to improve it then go from there. To be honest, its probably easier and less work to find a drop in fuel injected motor and swap it out rather than try and convert yours over. And if you go this route you might as well upgrade to a 496... just sayin

Oh don't think I haven't thought about that. I would have to change outdrives since I have one of the older AQ's. I guess it would theoretically be possible because later versions of the 252 (2001 models) had the 496 as an option.

See how we went from replacing a power valve to a total rebuild/re-power? You old boat guys just can't do anything easy, can you? lol

[Lockey14s]

Oh don't think I haven't thought about that. I would have to change outdrives since I have one of the older AQ's. I guess it would theoretically be possible because later versions of the 252 (2001 models) had the 496 as an option.

See how we went from replacing a power valve to a total rebuild/re-power? You old boat guys just can't do anything easy, can you? lol

hahaha we dont do anything easy because nothing is EVER easy! And it can snowball pretty quickly, especially for power hungry guys like us.

But I did forget you have the older drive. that would take some transom rebuilding to upgrade it to the DPS style drive.

[Lockey14s]

oops i screwed up the quote lol