A couple more I/O questions...

[guy48065]

My 2000 4.3L has a standard carburetor (not tks like I first thought), distributor cap & coil. There's also a black box I'm wondering if it's a rev limiter?

Also--what the heck are the 2 plastic tubes for that lead from the valve covers to up near the flame arrestor on the carb? On a car this would be the closed pcv system. Here it appears to be open at the ends.

 

[alldodge]

I'm unable to make out the numbers on the box but looks like a TBV ignition module

The hoses are there so that any blow by gets sucked into the motor via the flame arrestor

 

[Pmt133]

100% agree its a thunderbolt V, that should be a denso sticker. (Exactly what mine looks like)

Also looks like batwing 1 piece manifolds.

 

[guy48065]

So does this ignition module have a rev limiter or did that feature come later?

 

[Pmt133]

So does this ignition module have a rev limiter or did that feature come later?

About 150 rpm above redline... 4950 or so.

 

[StewartL]

That black box is likely the ignition control module, not just a rev limiter. It manages your spark.

Those plastic tubes are your PCV system. They're open to allow crankcase vapors to be drawn into the carburetor and burned, which is normal for many marine engines. It's a closed system that vents back into the intake.

 

[StewartL]

Hope it helps

 

[Scott Danforth]

it does look like the one-piece Batwing motor killing exhaust manifolds.

 

[Scott06]

My 2000 4.3L has a standard carburetor (not tks like I first thought), distributor cap & coil. There's also a black box I'm wondering if it's a rev limiter?

Also--what the heck are the 2 plastic tubes for that lead from the valve covers to up near the flame arrestor on the carb? On a car this would be the closed pcv system. Here it appears to be open at the ends.

View attachment 410648

yes that is a Mercarb not a TKS. The mercarb is the younger brother of the Rochester 2 jet, Mercruiser started making their own when GM stopped making carbs back in late 80's early 90s. you can tell it from a 2 jet because the mercarb will have one idle mixture adjustment screw vs two on the 2 jet. There may be a anti tamper cover on it depending on the year.

The box is the ignition module and does have a rev limiter built in as other have mentioned it kicks in around 5k. The thunderbolt ignition is a great system only downside is if the module dies they are either NLA or costly.

 

[guy48065]

it does look like the one-piece Batwing motor killing exhaust manifolds.

Background on this topic?

 

[Scott Danforth]

The batwings were a cost savings idea to make the elbow and manifold as one piece.

The truth is the castings failed killing the motors

 

[Lou C]

There was an article on another website about it, Merc apparently did this to save $50 per engine, due to the Vortec engines costing slightly more, and what caused the problem was that they couldn't get consistent wall thickness in the castings, so some had really thin areas that rusted through fairly quickly and let water in the engine. So Merc came up with a conversion kit to allow you to convert to the 2 piece design without changing the Y pipe, and Barr Marine also makes one.
I had OMC's version of the same thing (used from '85-'90) and they were not known for failure AFAIK and I had them on my engine from 2004 to 2017. I changed the original pair it came with in '04, then again in '11, and by '17 they were due again to be changed (salt water boat) but had long been NLA so I converted mine then to the 2 piece system OMC changed to in '91 and Volvo used after they bought out OMC's sterndrive division right up to when they had to change to the dreaded cat converter exhaust.

OMC Cobra Batwings

OMC with 2 piece conversion using Barr Marine manifold + elbow and Volvo Penta 90* downpipes and hoses....fit perfect no leaks!

 

[guy48065]

The batwings were a cost savings idea to make the elbow and manifold as one piece.

The truth is the castings failed killing the motors

What percentage failed?

 

[guy48065]

I have these chunky manifolds. They're 1-piece but they don't look like the "batwing" shape in the photo.

 

[Lou C]

Those are Merc's Batwings, same idea cast all in one piece.
Besides saving money the one really good aspect of the design was no gasket to leak between the manifold and elbow. But the difficulties in the casting process caused so many warrantee claims I'd think that Merc quit making them.

Barr Conversion Kit for Mercruiser V-6 GM 4.3-Liter from One Piece to Two Piece

Barr Conversion Kit for Mercruiser V-6 GM 4.3-Liter from One Piece to Two Piece

marineengineparts.com

here's an easy way to remove the risk of hydrolocking your engine if and when the batwings fail.
this place is kind of local to me, when I buy exhaust I get it from them and don't have to pay shipping
the risk of not changing it is that you won't know a failure is eminent till it happens then you'll have water in one cylinder or more. If you try to crank the engine over not knowing why the engine won't crank you can bend a connecting rod. Many think it's a starter problem when in fact it's not, water in a cyl can't be compressed, if you try to start it you can bend a connecting rod!

 

[guy48065]

Lou I don't see an easy fix here.

 

[Lou C]

It is, you just replace the whole exhaust system with the one I linked above, pricy but can avoid ruining an engine. For us in salt water we have to do this every 5-7 seasons. My engine is on its 4th exhaust system and probably will get at least new elbows at the end of this season.