‘97 4.3 2bbl to 4bbl!

[jkimball]

cap it.

Ok thanks!
assuming just use the standard silicone vacuum caps? No risk from capping since I have the electric fuel pump?

 

[Scott06]

That is not a fuel return line it’s a overflow tube such that when a Marine mechanical fuel pump has a diaphragm rupture the fuel that would **** out of an automotive pump is Directed through this tube into the carb and into the engine vs causing an explosion hazard.

not sure if it was mentioned else where merc part number 805359T is the throttle bracket they used with the Webber/edlebrock 4 bbl. this will mount the electrical components and fit the throttle linkage clean and easy.

 

[jkimball]

That is not a fuel return line it’s a overflow tube such that when a Marine mechanical fuel pump has a diaphragm rupture the fuel that would **** out of an automotive pump is Directed through this tube into the carb and into the engine vs causing an explosion hazard.

not sure if it was mentioned else where merc part number 805359T is the throttle bracket they used with the Webber/edlebrock 4 bbl. this will mount the electrical components and fit the throttle linkage clean and easy.

Right, which is what I understood it to be. Although I called it a return line.
With the electric pump, I don’t believe I have a use for it. So I suppose I’ll cap it.

I did order the bracket you mentioned above. I’m wanting to do this as cleanly and near OEM as possible. So I hope the breaker/solenoid mount up to it.

 

[jkimball]

Any advice on what type of NPT plugs to use in the bypass holes? Naturally I would shy away from mixing brass and aluminum- but since this is an aluminum manifold with brass inserts it kind of makes me question what knowledge I have of the galvanic chart....
should I use stainless, brass, or standard steel? Not really wanting steel Bc I want to avoid rust if possible.

 

[Scott06]

Brass is fine

 

[jkimball]

Just to close the loop on the swap I wanted to report back and post some pics.

Spent the day Saturday turning wrenches and got her on the water Sunday. Pretty happy with the results! Feels like it has a little more grunt low end, maybe not a ton but where it really shines is mid range 3,500 - 4,000 rpm.

The throttle response is much snappier and it’s actually considerably quieter than the 2bbl.
Cold starts are almost instant, however I am getting a little heat soak after she warms up that makes warm starts a little more prolonged.

I’m pretty sure this is definitely due to me just mounting the carb directly on the manifold using the supplied carb gasket.
So yesterday I ordered a 1/2” phenolic - wood spacer to help insulate it a bit and hopefully eliminate the heat soak.

Would I say the upgrade is worth the $$ if I didn’t already need a new manifold and carb... too early to tell I think. But since I was looking to replace the manifold and carb or have it rebuilt anyhow - they extra $200 I have invested in this over a rebuild back to OEM definitely seems to be worth it. At least initially.

 

[nola mike]

Just to close the loop on the swap I wanted to report back and post some pics.

Spent the day Saturday turning wrenches and got her on the water Sunday. Pretty happy with the results! Feels like it has a little more grunt low end, maybe not a ton but where it really shines is mid range 3,500 - 4,000 rpm.

The throttle response is much snappier and it’s actually considerably quieter than the 2bbl.
Cold starts are almost instant, however I am getting a little heat soak after she warms up that makes warm starts a little more prolonged.

I’m pretty sure this is definitely due to me just mounting the carb directly on the manifold using the supplied carb gasket.
So yesterday I ordered a 1/2” phenolic - wood spacer to help insulate it a bit and hopefully eliminate the heat soak.

Would I say the upgrade is worth the $$ if I didn’t already need a new manifold and carb... too early to tell I think. But since I was looking to replace the manifold and carb or have it rebuilt anyhow - they extra $200 I have invested in this over a rebuild back to OEM definitely seems to be worth it. At least initially.

In the middle of this now (plus some). What size jets/rods/springs did you use?

 

[jkimball]

Hey Mike - sorry for the delay, haven’t been on in a few weeks.

I just used the carb as it came out of the box and it runs incredible. Zero bogging issues or anything. Idle a great, great top end and responsiveness