Considering going from 500 efi to intakes and carbs
 

Looking for opinions. How difficult? Any downside? I have 3 of these in my 2000 43 Scarab AVS. They are 25 years old now and with some of the stories of NLA injectors failing and leaning out and trashing engines I thought about going to carbs. Thoughts? Thanks in advance for your replies.

That would be a lot more grief and money than just buying different injectors and have the ECU's tuned.

You'd possibly gain hp from 5000 / 5200 up and give up 4 times as much torque from idle to 4500 due to runner length. IF your engines have stock cams that are done by 5400/ 5500 youd most ;likely end up going down a pitch in prop to get it to drive the same and in end fight to get it to drive as good as it currently does assuming its dialed in currently. Runner length dictates tq, you have 14.5" runners currently, most intakes have 3" to 6" runners, personally I wouldnt do it unless you plan other mods, Smitty

Who tunes ecu's and what injectors do I buy? Thanks.

I was really hoping it would be a simple swap. I didn't think there would be much difference between my motors and the old 500 hp blue motors. I think they came with single plane intakes.

I did it but completely had new engines built and just used the 500efi accessories and part of the wiring harness. Best move I made getting Rid of the efi. I’m old school so I like tuning on carburetors. This is in a 2003 30ft twin step cigarette mystique.

https://cimg0.ibsrv.net/gimg/www.off...bc6a5afa1.jpeg

Articfriends is correct. I have HP500EFI's and just use injector cleaner every other tank of fuel. They have around 780 hours on the motors and run great.

My engine builder (RIP) had a combo where he used the stock intakes with a 540 cu in kit and out of the box AFR heads. The thing had 700LB of TQ at 3500 rpm and made about 640 HP. That is some killer TQ for a NA motor and what we need most of the time.

You can seek higher HP but those intakes unless modified are not good at it and you normally lose low end TQ.

It's not a race boat.

Nice setup cig 28. Looks sweet. Exactly what I had hoped to do. What carbs and intake are you using. And look, no $900.00 thermostat housings that you can't even buy anymore. I take it you couldn't continue to run the stock ignition?

In looking around I was maybe thinking about something like this.

https://www.hardin-marine.com/p-1356...oval-port.aspx

Are you still running your stock injectors? What injector cleaner are you using? I always overdose my boat with Seafoam every time I fuel up.

Are you running electric fuel pumps on these? If so, can you post up some pics of fuel system and what all you did. TIA, beautiful work!

With twins, I would plumb thr guel oumps so 1 can feed both engines if 1 of the pumps fails.

Or better yet, have a 3rd pump as an emergency pump that is self pressure regulated.

You may not get full flow for WOT, but the intent is to be able to cruise and get home.

Filtered fuel to the pumps, mounted to reduce lift to the pump.

Yes still running stock injectors, had them cleaned and flowed years ago. Only after sitting while I was redoing transom did I have one fail, OPEN!

That was crazy.

Seafoam or Lucus injector cleaner.

BTW you posted a Oval port intake, HP500EFI's are rectangular port.

I make the same #'s with 540, Dart 308 iron head, 525 efi cam, Bill Mitchell single plane intake, 850 QF carbs, 1'' carb spacer, DUI ignition, Tq is 700 @ 3900 & HP 638 @ 5200.

Originally had 540 with 502 mpi intakes, 308 darts and tuned computers, was a bear to 3500 where it would hit a wall and lay over, I'm guessing the intake/cam combo was an issue. I bought the boat that way.

Never tried the MPI intakes.

I guess it comes down to if the OP wants to spend money on new intakes, carbs etc. Or just use what he has. Of course the 540 I talked about had different injector so took care of that. Options, Options.

Bill Mitchell intake and AED carburetors.

no I’m using mercurys setup that the later model 500 efi used as a lift pump to get fuel to the electric pump. They are mechanical pumps.