'78 OMC 140 TBI Conversion

[Red0ktober]

My brother acquired a '78 Fiberform (18ft) with an OMC 140 engine and OMC 400 Stern Drive. I'm the mechanic of the family, so surprise surprise, it's parked at my house. It supposedly ran a few years ago, but has been sitting since, with about 20 gal of fuel in the tank.

I've been able to get it to start with some starting fluid and it will sustain itself with the throttle held open, but it will not idle or rev quickly. I've since drained the tank of old fuel and now I'm waiting on a new fuel filter before I try again with fresh gas.

If it still won't run reliably, I may just tell him that the boat won't be ready this season and convert it to fuel injection for next season.

I realize the OMC 140 is not an Iron Duke engine, but I suspect an Iron Duke distributor may bolt in. If that's the case, we may be in business. I'd just need to make an adapter plate for the TBI, drill it for a coolant temp sensor, an O2 sensor, fabricate a surge tank for the high(er) pressure fueling, burn a new chip for the ECU, etc, etc. Easy as pie.

Marine TBI Conversion on a 4.3L: http://home.hiwaay.net/~davida1/boat.htm

Thoughts?

 

[Bondo]

Re: '78 OMC 140 TBI Conversion

My brother acquired a '78 Fiberform (18ft) with an OMC 140 engine and OMC 400 Stern Drive. I'm the mechanic of the family, so surprise surprise, it's parked at my house. It supposedly ran a few years ago, but has been sitting since, with about 20 gal of fuel in the tank.

I've been able to get it to start with some starting fluid and it will sustain itself with the throttle held open, but it will not idle or rev quickly. I've since drained the tank of old fuel and now I'm waiting on a new fuel filter before I try again with fresh gas.

If it still won't run reliably, I may just tell him that the boat won't be ready this season and convert it to fuel injection for next season.

I realize the OMC 140 is not an Iron Duke engine, but I suspect an Iron Duke distributor may bolt in. If that's the case, we may be in business. I'd just need to make an adapter plate for the TBI, drill it for a coolant temp sensor, an O2 sensor, fabricate a surge tank for the high(er) pressure fueling, burn a new chip for the ECU, etc, etc. Easy as pie.

Marine TBI Conversion on a 4.3L: http://home.hiwaay.net/~davida1/boat.htm

Thoughts?

Ayuh,... Welcome Aboard,...
I see Alotta Wasted effort...

It'll still be a 140 hp. Stringer 400, only with an illegal ignition, 'n induction system..

 

[U.S.S. Too Tall]

Re: '78 OMC 140 TBI Conversion

Bond-O, illegal? Why is it illegal? Because it was not the stock set-up? It sounds like Red covered the explosion issue.

In the link, Red said that boat went from 40 MPH to 50 MPH, that sounds GREAT to me!!!

Sorry, still a newbie, I dont know the laws yet...

 

[Red0ktober]

Re: '78 OMC 140 TBI Conversion

I think the boat is more likely to catch fire as it sits than with a sealed injection system. But lay it on me, what are the regulations?

It's not 140HP right now, because it doesn't run. It's zero HP. I can convert it to injection for cheaper than a new/rebuilt carb.

Injection > Carburetion, always.

 

[Jason89sunbird]

Re: '78 OMC 140 TBI Conversion

Some of these guys can't think outside the box that's in the box lol.. The tbi ignition is the same as the boat efi versions and has a better advance curve. The tbi unit is also marine safe, just make sure you have no fuel leaks... I stayed carb when I upgrade my 4.3 to vortec and 4bbl.. I have a 454 tbi unit that has a spread bore adapter sitting around, tempting

 

[Red0ktober]

Re: '78 OMC 140 TBI Conversion

I'm hoping that Iron Duke dizzy bolts up, but worst case, the ECU could be used for fuel only and the old points ignition retained. Not my favorite option, but an option.

Poked around summit racing. All you'd need is to do is sandwich a couple adapters to go from the small pattern Rochester to the 3-bolt TBI. $60 for the set, or you could fab your own. I think I'll just buy them. [edit: actually, that base Rochester adapter doesn't look like it will overlap properly with the TBI throttle bores, might have to fab or modify]

Carb adapter:

TBI Adapter:

My [brother's] boat:

My other TBI project
1990 Isuzu, 2.8L upgraded to 3.4L with injection from 4.3L:

 

[Red0ktober]

Re: '78 OMC 140 TBI Conversion

Here are the Holley [expensive] adapters, looks to be a better alignment though. Trans-Dapt centers the bolt pattern, but Holley centers and transitions the throttle bores.

[edit, AGAIN: Upon a third look, the Trans-Dapt plates shown earlier do appear to be centered on the throttle bores, but have less 'meat' than the Holley and the TBI plate isn't transitioned towards the carb opening. The lower Trans-Dapt plate could be transitioned, but the gasket surface could end up pretty narrow at the edge if too much material was removed.]

Rochester:

TBI:

 

[bruceb58]

Re: '78 OMC 140 TBI Conversion

Please explain how you are going to have an O2 sensor work in a wet exhaust.

Like Bondo said, no matter what you do, you still have an OMC stringer...and that's the worst part of the whole deal.

 

[bruceb58]

Re: '78 OMC 140 TBI Conversion

The tbi ignition is the same as the boat efi versions and has a better advance curve.

Please explain why its a better advance curve. Also, please post the curves of these distributors. Would love to see them. Make sure they are the curves for the 4 cylinder that the OP is planning on using.

The tbi unit is also marine safe, just make sure you have no fuel leaks...

The fact that it is using a non-marine fuel pump and also using a fuel return path to the fuel tank(also not allowed) makes it NOT marine safe.

 

[Jason89sunbird]

Re: '78 OMC 140 TBI Conversion

Redotober I have done a 3.4 from iron duke conversion in an S-10 with a 4spd and 4.10 gears in the rear, LOVED IT. I kept the camaro sfi injection and manifold. It dyno at the wheels 148.9hp and 192ftlbs. I hauled my Matco 3 bay tool box in a uhaul trailer (about 5k lbs, truck weighed 3150) from san diego to salem oregon, ran like a champ. On the grapevine i maintained 55mph up the hills. They sell o2 sensor adapters on ebay for merc v6/v8 wet manifolds. Don't know about the 4cyl version. Bruceb58 As you have already posted before (1989 4.3 OMC cobra resistor replacement) the points curve of a 4.3 was 6 degrees advancement at 3200. The delco est dist has 20 degrees advancement and 16 degrees by 3000 rpm based on jtybt15 experience; http://www.boatered.com/forum/topic.asp?TOPIC_ID=129999

 

[bruceb58]

Re: '78 OMC 140 TBI Conversion

The Delco Voyager EST distributor for the 3.0 is 13 degrees total advance(relative to initial idle timing). This is from the Volvo 3.0L manual which is the same engine.

 

[Jason89sunbird]

Re: '78 OMC 140 TBI Conversion

That's still 3 degrees more then the points curve from the chart you posted lol. The true benefit of the est is 110 miliamps of spark it delivers vise 40 miliamps for points.......... I would never run points, I did find out how to properly run the esa circuit on the merc part of the forums. Don S is a good source of info. You delete the ESA module and wire the micro switch to run 12vdc to pin B on the 4 pin plug to the delco dizzy.

 

[Red0ktober]

Re: '78 OMC 140 TBI Conversion

Please explain how you are going to have an O2 sensor work in a wet exhaust.

Like Bondo said, no matter what you do, you still have an OMC stringer...and that's the worst part of the whole deal.

Where there's a will, there's a way. I'll figure it out, or run it open-loop which is still better than a carb.

The fact that it is using a non-marine fuel pump and also using a fuel return path to the fuel tank(also not allowed) makes it NOT marine safe.

Having a rod sticking inside the engine to thrash around a 34 year old diaphragm sounds like a better idea. A modern electric fuel pump doesn't have a glass bulb to catch fuel when it breaks because it won't spew fuel into your engine bay when it breaks.

Redotober I have done a 3.4 from iron duke conversion in an S-10 with a 4spd and 4.10 gears in the rear, LOVED IT. I kept the camaro sfi injection and manifold. It dyno at the wheels 148.9hp and 192ftlbs. I hauled my Matco 3 bay tool box in a uhaul trailer (about 5k lbs, truck weighed 3150) from san diego to salem oregon, ran like a champ. On the grapevine i maintained 55mph up the hills. They sell o2 sensor adapters on ebay for merc v6/v8 wet manifolds. Don't know about the 4cyl version. Bruceb58 As you have already posted before (1989 4.3 OMC cobra resistor replacement) the points curve of a 4.3 was 6 degrees advancement at 3200. The delco est dist has 20 degrees advancement and 16 degrees by 3000 rpm based on jtybt15 experience; http://www.boatered.com/forum/topic.asp?TOPIC_ID=129999

I ran the SFI on my Trooper for a while and loved it, though I had a problem with my O2 wiring and it hogged fuel (I found the problem when I was disassembling the harness). I took my engine apart to change the cam (Crane H260-2 with Comp pushrods, springs, and 1.6 ratio rockers) and use different intake manifolds to fit the engine bay better (from earlier 3.1L Camaro), and long story short, TBI was the way to get the truck back on the road before winter... a couple winters ago. I still have all the SFI gear and someday I may reinstall it, but for now it just works!

Thanks for the info on the dizzy, I'll look into those too. I can salvage yard a 'Duke dizzy for pretty cheap. If that fits, I can lay in whatever curve I want into the ECU.

Mocking up the 3.1L manifolds with the Fiero valve covers (I wish I would have repainted them the original orange).

My SFI setup, I had to run dual 10" fans down low to clear that 90? turn to the filter.

Since my 3.4L has a crank sensor, I retrofitted the DIS ignition to the TBI setup.

 

[Bondo]

Re: '78 OMC 140 TBI Conversion

Ayuh,... Still sounds like a wasted effort,...

You'll end up with a $500. boat, with a custom $1500. induction system...

It's an OMC Stringer 400...aka, a polished turd...

 

[Red0ktober]

Re: '78 OMC 140 TBI Conversion

You've posted on this message board 37,710 times, with only 500 being helpful or positive. Why don't you just let me light this boat on fire in peace. I'll get rid of one more Stringer 400 in the process, won't that make you happy?

 

[Scott Danforth]

Re: '78 OMC 140 TBI Conversion

Nothing wrong with a stringer 400 if you can make your own parts because you usually cant get them anymore with the exception of a lower casting as its the same as the V4.

however automotive TBI on a boat is not a good idea. if you want a simple TBI, just simply pick up the holley Marine Pro-jection unit (coast guard approved). however I recommend to just rebuild the carb and use the boat until the outdrive goes to hell.

 

[bruceb58]

Re: '78 OMC 140 TBI Conversion

That's still 3 degrees more then the points curve from the chart you posted lol.

I never posted the curve for the 3.0L engine.

 

[Howard Sterndrive]

Re: '78 OMC 140 TBI Conversion

Thoughts?

why not put the effort into a V6 conversion? Then you'll have a performance improvement.
18ft and 140HP sounds kinda boring.
fuel injection to a top speed of 35 with the motor screaming at 4500 rpm ... I guess if fishing is the objective, 140HP is ok.

I added 10mph top end speed to my 18 footer, removing the 140 and putting a V6 in... and my insurance company will insure the boat because it has all SAE J1171 rated components on board.

You've posted on this message board 37,710 times, with only 500 being helpful or positive. Why don't you just let me light this boat on fire in peace. I'll get rid of one more Stringer 400 in the process, won't that make you happy?

you asked for thoughts, Bondo gave you his thoughts.
You should have specified, "only post a reply if you think like I do" in your original post if you don't want voices of experience.
Often, experience = pessimism around boats. especially when 400 stringers are involved.

 

[U.S.S. Too Tall]

Re: '78 OMC 140 TBI Conversion

why not put the effort into a V6 conversion? Then you'll have a performance improvement.
18ft and 140HP sounds kinda boring.
fuel injection to a top speed of 35 with the motor screaming at 4500 rpm ... I guess if fishing is the objective, 140HP is ok.

I added 10mph top end speed to my 18 footer, removing the 140 and putting a V6 in... and my insurance company will insure the boat because it has all SAE J1171 rated components on board.

Often, experience = pessimism around boats. especially when 400 stringers are involved.

His other post states that he got an extra 10 MPH just out of a EFI set-up. Why pull an engine out, replace with heavier engine, which is probly over the USCG engine limit for that boat? When you can drill a few holes in the block and make that 10 MPH with fuel injection?

From the look of the picture, his brothers boat looks to be about the same as mine. A 16' 11" bow rider. The HP limit on mine is 140. Which is what I have, thankfully!! Swapping out a carb or EFI, doesnt really change the HP too much, just the amount of fuel flow.

Also, I do have this "dreaded" Stringer 400. I have not seen anything wrong with it. The only issue is finding parts. Which I believe I have found a few websites that look to have a great selection of stringer parts.

Just my 2 cents worth...

 

[bruceb58]

Re: '78 OMC 140 TBI Conversion

His other post states that he got an extra 10 MPH just out of a EFI set-up. Why pull an engine out, replace with heavier engine, which is probly over the USCG engine limit for that boat? When you can drill a few holes in the block and make that 10 MPH with fuel injection?

I don't know if you read the link but that boat was not running right in the first place. He was only getting 3500RPM out of his engine. He should have been able to go way faster with his original set up. TBI is not much better than a carb performance wise. In fact, its bascially just a carb body with a couple injectors instead of a venturi with jets. You could possibly get more HP with a MPI but that's not what he did.