Hello everyone! First post here so I hope its in the right spot.

I have a question about converting my new boat from EFI to carb. I tried doing some research but this is a little more specific. I have a 1990 Baja 226 sport with a Gen IV 454 that got water in it and froze this past winter and the block cracked after it was just rebuild two years ago. This lead me into my new to me boat that is a 96, 26 Hustler Sport. Since I got it, its had a few issues and Ive been trying to work through them. I just sent the injectors out this morning to be ultrasonic cleaned and flow tested so well see how it goes when they come back but hopefully that's the last of the issues. I have been reading a bunch on here and it sounds like sometimes swapping to a good carb setup from MEFI1 is the way to go. Since I have the other boat with possibly all the parts to do it, I'm wondering if I can pretty easily. The only reason I am even considering it is because I had the Baja for ten years with the same setup and that boat NEVER missed a beat. Cold starts, hot starts, WOT runs, no hiccups coughs or anything. It was rebuilt two years ago so its quite unfortunate that it froze but here's a list on both
Motor 1/Baja:
Gen IV 454, .30 over. Made 490/520.
Merlin rec heads that were recently ported. I cant find anymore info on them but the numbers on the casting are "1-043", "9C" and "H02 I"
Unsure of cam spec
Edelbrock RPM air gap intake
Holley 800 or 850 CFM double pumper 4 barrel. "6R 3767 B"

Motor 2:
Boat was originally a Gen V 502 with MEFI1. The long block was swapped in 2016 for a Gen VI.
Rec port stock heads
VST
Stainless marine manifolds and risers


My main question is, can I move the intake, carb, fuel lines, coil etc over to the 502? If I can/did, is there anything specific I should look at to control it ignition wise? Also, I know the 454/502 difference but would the ported heads from the 454 be able to be swapped to the 502? I read going Gen IV to VI is ok as long as you use the correct HG. If so, would there be any gain?

Does one or both have roller cam and lifters, distributors may be different or at least the gear if one is a roller and the other is not.

GPM makes a good point on the Distributor gear. Often in complex swaps like this, those little things get missed.

Putting a Carb on an EFI engine generally is not a complex project, but there are important factors like correct head gaskets ( as you mentioned) to use...and the wrong ones will still fit up.

Daytona Sensors has a really good ignition...digital and programmable for Carbed engines. You should be able to use the EFI dist for that...or lock out your carbed dist. Someone can chime in on using the EFI dist with the Daytona.

The 088 style rec port heads are pretty big...and really need a lot of cubes to come alive...or run them at high rpm. The exh ports are restrictive. But if they are in good shape...then run them.
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Your carb intake will fit, but you may want to match up the ports, or not, just to test it out.

The 502 will likely have a roller cam.

Do the Stainless Marine exh manifolds have O2 sensor bungs? That would be beneficial going carb to dial it in. If you don't spend the time to tune it...you won't get as close to the EFI mileage or running manners.

Your EFI fuel pump pressure will be too high for the Holley 850DP...so swapping your old one if elec is easy.

The Merlin heads you have on the Mark IV look to be the same setup as the 088 Rec port heads. 2.19/1.88 valves with 119cc chamber. Around 320cc intake. Circa 1995-96.

If you're doing your own work, I would just change the manifold over...and run it up. Then make head changes later if you find the need. If you're paying to have it done, then heads right away if you want to go that route as less labor in the long run.

Good luck with the switch.

I just did this, the previous owner swapped a 502 into my 96 Baja put the 454 it was born with s EFI on the 502 including the MEFI-1 with no programming changes. Boat ran ok but never right then it popped a head gasket. I purchased Holly EFI for the new 509 but its on B/O so in the mean time Holley sent me a 850 carb so I am not out the entire season until the HP ECU arrives.

I am going to be running the same fuel pump on the carb that I will be using on the EFI but I had to get a regulator that can step down to 7psi for the carb and when I go to EFI swap out the reg to the one originally ordered for EFI. My distributer and ignition boxes are different for the carb and EFI as well. My engine is a Gen 6 roller and Im running the melonized gear on both distributers I have since the EFI and carb is different as well. This has been a SH*TSHOW to say the least.

If your interested in the parts list myself and Holley worked on I would be more than happy to share.

Why not take the distributor, coil, and module off the 454 and drop in the 502 with a good single plane and a 950/1000cfm annular Holley?
Did Merc use an iron gear on their roller cams? If so all is good. If not then use a melanized gear.

I appreciate that! I tried PM’ing you but can’t because I don’t have enough posts. Anyway you can try to PM me, if not I’ll give you my email

that’s what I’m gonna do, what’s a rec for a good single plane?

In this setup, your 502 will want a dual plane - a single plane with stock heads and the small GM cam will hurt torque production with no upper rpm gain.

Merc’s 502 MPI cam requires the melonized gear.

This is what I ended up doing. Have an air gap coming tomorrow, and bolt my carb onto that. Removed my VST and keeping the mechanical with -8 lines. It seems like I have 3 options, but someone please tell me if I’m wrong.


A) I have a wiring harness, distrib, coil + thunderbolt iv for the 454 (which is a “V8-24” module with a merc racing dist. Do I use that on the 502 and just set the timing accordingly? Instead of 8*BTDC, it would be …?? This is where I’m lost.

The factory thunderbolt for the 502, which I do not have, is “V8-20R”.

B) I also have a wiring harness, from a TB V 454 with the module, harness and distributor. I could use this and set the timing to?


C) use one of the TB harnesses with the original EST ignition coil, module and distributor that was from the MPI setup and act as if it were the est upgrade kit.

any help would be fantastic

Keep the EST. You can buy the pig tail on Amazon for less than $20 or take what you need from the injection harness and splice (I went this route).

Diagram for the EST below. Ignore the 4-pin connector - you’ll no longer need to plug anything into it.




The distributor shown is for a MOPAR adaptation of the GM module so don’t worry about those. You’re interested in the + and C connections.

Set your total timing at 3k rpm. 32 degrees total is probably good on a stock iron-head 502.