View Full Version : Carb to fuel injection

07-13-2006, 09:44 PM
I have a 1998 Mercruiser 4.3 Vortech V6 in my boat. It has a Weber 4 barrel on it. Is there anybody that makes a kit to convert it to fuel injection. Thanks Shawn

07-13-2006, 09:50 PM
Momar injection in Colorado. 303 618 4140.

07-13-2006, 10:50 PM
"Edelbrock, Holley and a bunch of others make aftermarket systems. You could also go with the same system used on Mercruiser boats or check into GM performance parts. www.truckperformance.com ("") may have something, too.

Why does it have a Weber 4BBL when they come with Rochester?"

07-14-2006, 09:20 AM
"I agree with the above posts... many quality kits are available. I must say though, I really like the Webbers. They are easy to work on, adjust and are pretty much bulletproof. That's what you want out there miles from land IMHO. Plus, if you want to change your fuel curve it takes 15-20 min.

I'm curious, why go to EFI?"

07-14-2006, 01:00 PM
Thanks for he response

Jim it came with a Weber new. It looks just like a Rochester but says Weber on it.

Bill It runs good with the Weber. I just like how the fuel injection starts when it it cold and seems to be a little more responsive. Don't get me wrong it runs great with the carb. just looking to see if anything else is available for it.

07-14-2006, 02:46 PM
"WOW! I don't think I've ever seen a Mercruiser with anything other than Rochester. Maybe it was an attempt at fixing their problem with run-on, which was pretty bad on the 4.3L Vortec motors. Still a good motor, though.

Personally, I hate carbs. They're a cheap, easy way to get gas into the engine but I don't like the problems. You might check into shopping around for the sensors, harness and ECM from car parts suppliers. Standard TPS (non-Corvette), MAP, ECT and knock sensors, Delphi ECM (MEFI 4) and harnesses are available. The tricky part will be getting the right program for it, which won't be from SuperTuner, etc. You may be able to get an ECM with a Chevy pickup program to use as a baseline from GM performance parts. Call around to see if any speed shops near you work with TBI systems and if they have the hardware, software and a technician who can acquire data, analyze it and make the proper changes for your application. I know someone in Indiana who can but it wouldn't be cheap. His shop is usually busy doing development work for GM, Delphi, MasterCraft and Indmar.

Another option would be to find a scrapped boat with a good drive that has the TBI on it. That way, you would unplug the motor from the boat harness and replace yours with it. If it's a Mercruiser, the motor side of the harness is the same pin configuration, but I would still check around for a diagram. You would strip your motor harness off, install the sensors and install the harness from the other motor. The program should work for your boat if the donor boat is a similar size and weight."

07-14-2006, 05:27 PM
"Jim I have that same "run on" problem you are talking about so the weber didn't fix it. I have tried mercruiser suggestion with colder plug, better ventilation, etc. It still does it. It run's great with the exception of the "run on" problem. I was thinking fuel inj. would cure it. Holley makes some that are marine and some that are automotive. I wonder what the diff. is. Here is one I was looking at http://www.affordable-fuel-injection.com/marine-fuel-injection-systems.htm ("")"

07-14-2006, 06:00 PM
"Mercruiser had a solenoid (it was a service kit for your motor) that was activated when the key was turned to ON and basically replaced the idle stop. When the key was turned off, the solenoid retracted and the carb was set so the idle speed was effectively 0 RPM, so it completely closed the throttle plate. It actually works."

07-14-2006, 06:20 PM
WOW how do I get one of these? That would be great. Like I say the motor runs good I am just tired of this "run on" condition. Thanks Jim

07-14-2006, 07:15 PM
"Any Mercruiser dealer can get them and there was a service bulletin for this issue in '98, IIRC. The part number is on the bulletin along with the rest of the other things to try. I don't think I had to use the others on the list after installing the solenoid but that was a lot of boats ago. Make sure the gas is fresh (and keep the octane up), don't shut it off right after a long, hard run and definitely let it cool down after long runs in hot, dry weather (when detonation is more likely to occur). You may be able to go back to the MR-43T plugs or whatever it came with. The Vortec may have come with MR-43LTS (I know the 8 cylinder came with those) but refer to the flame arrestor cover to be sure.

One thing to be concerned with re: the run-on is ingesting water. If the motor just will not crank after it runs on, pull the spark plugs and crank it over to clear the water from the cylinders. If you don't do this and keep trying to crank it, you'll kill the starter."

07-15-2006, 02:14 PM
Jim I went by my mercruiser dealer today. They didn't have a clue what I was talking about. "I was afraid of that around here" Any other ideas on where I can get that part/ part #. Thanks Shawn

07-15-2006, 03:20 PM
"The only problem with service bulletins is that not enough people read them. Your dealer should at least have the integrity to look for it. I assume they have a service manager and at least one person who does admin stuff. Or, they could call Mercruiser and ask. ANY Mercruiser dealer has access to this info and if you are in a warmer area of the country and they don't know about this, they are way behind on their training.

Whoever looks for this bulletin will need the serial number of the motor, so post it here and if anyone has access to it, they can help out."

07-15-2006, 06:14 PM
Make your own. Take one from a old chevy and wire it so it opens when the key is turned on and will close with the key off. Its the same idea they used on cars starting back in the 70s. Idle control solenoid. (ICS)

07-15-2006, 10:58 PM
What cars came with these so I will know where to look? Thanks

07-19-2006, 07:24 AM
""Run on" problems in a boat? You've got to be kidding! Those problems, in cars, were in the early smog era, when engines were run lean as heck to reduce pollution. There's absolutely no reason for a boat engine to do that, especially since the motors run cooler than in a car.

Two things cause run on: a too lean idle, and/ or too high an idle speed. Both are easily adjustable witha mere screw driver--try changing it with an EFI system!


07-19-2006, 10:06 AM
"Jeff- Mercruiser had a big problem with it when they made some changes to their motors in the late '90s. the 4.3L was the biggest offender and even after enriching the mixture, they still did it, in a lot of cases. The idle speed could be dropped to 500 and they would still do it, especially in hot weather. You can't easily adjust the idle or mixture on an EFI system, but they don't run-on, either. Cars are still run lean because the EPA and C.A.R.B. still want to see zero emissions and because some companies are trying to make cars use less fuel. Boats haven't been mandated to run as lean as cars but C.A.R.B. has all but eliminated 2 cycle motors in California and they got rid of MTBE after finding it in ground water. For the 2007 model year, Indmar is introducing motors with catalytic convertors and 02 sensors.

Because scanning the service bulletin and posting it on the web will probably get me in trouble, I'm including the possible causes listed and the suggestions to minimize the issue here. The boats I worked on still ran on after going through the whole list and I ended up installing the Mercruiser "last resort" kit, which is an idle stop solenoid and that fixed it.

"These conditions include but are not limited to:
1. Type and formulation of gasloine in the area.
2. Type of boat and engine compartment ventilation system.
3. Outside air, inside engine compartment ait and engine coolant temperatures.
4. How quickly the engine is shut off after running or cruising at high RPMs.
5. How the boat and engine are operated.
6. Engine idle RPM set too high.
7. Wrong heat range spark plugs with deposits on them.
8. Deposits in combustion chamber.

Suggestions to minimize 'Run On'

Items 1,2 and 3 can correct or reduce most of these 'run on' problems. Letting any engine idle a minute or two before shutting down is desireable. This helps the engine to normalize at idle RPM before shut down.

1. Be sure engine idle mixture, idle RPM and ignition timing are correct. On engines with Thunderboat IV ignition, setting the idle RPM as low as possible can help stop 'run on'.
2. Adjust throtte cable barrel so that the carburetor's throttle lever returns to the idle speed stop every time the remote control throttle lever is returned to neutral, idle.
3. Idle engine 1 to q-1/2 minutes before turning key off after running at cruise or higher RPM.
4. Try a different brand of regular fuel or try some premium fuel.
5. Increase the idle mixture by 1/8 turn 'richer'.
6. Go to the next colder heat range spark plugs.
7. V6 and V8 only: install a 140 degree F thermostat.

OEM spark plugs:

Short reach- AC MR43 T

Short reach replacements:

NGK- none
Champion- RV-12YC or
Champion RV91MC

Long reach plugs:


Long reach replacements:

AC- none
Champion- RS9YC"

This is directly from Mercuiser service bulletin 97-17, revised July 1999. Original bulletin was from July, 1997.

The "last resort" parts kit I referred to in Mercruiser part # 862656A3 (4BBL Weber carb) or 862656A2 ( Mercarb 2 BBL) and the list price is $294.35, but I would check for best price. I'll see if there's an aftermarket equivalent.


07-19-2006, 04:56 PM
Jim do you think you could post a picture of that kit. I bought a Idle Stop Solenoid for a rochester that goes on a 1979 Buick that I think I can make work. If you had a picture of that "kit" it sure would help alot. Thanks

07-19-2006, 05:36 PM
"I don't have a photo but if you go to a Mercruiser dealer with that part number, they can look in Midas (Mercruiser's parts software). It won't be a great picture but it should work. Take the serial number of your motor with you when you go."

07-19-2006, 05:59 PM
Ok Jim thanks for all your help. I will post at a later date to give an update. Thanks again.