Fuel tank size and usage

[J-Rides]

Hey everyone, I have an '86 340 Express Cruiser with two Merc 260's - that's the 5.7L Chevy Small Block. Each engine has a 4 barrel quadrajet carburetor, from what I understand. I will confirm before I do any tuning on them, but I think that's what came stock on these engines.

From my manual it appears as if I have two 102 gallon fuel tanks for a total of 204 gallons. However, my experience is telling me that either I have the smaller tanks (72 gallon port and 80 gallon starboard) OR one of my new fuel senders is reading wrong, OR my port engine is burning considerably more fuel than the starboard engine.

Can anyone tell me if the EC ever came with the smaller tanks or did they all come with the twin 102 gallon tanks? Again, when I look in the manual it would appear I have the twin 102 gallon tanks but something is not adding up. I obviously hoping this is just a matter of the fuel senders reading wrong.

My other issue is that both engines smell like they're running rich - both at idle and at a reasonable cruising speed of about 7-9mph. Is that normal? I've done quite a bit if snowmobile carb work, but never done carbs like this... maybe its time I learn. I do plan to pull some plugs this weekend and try to get a read on how they're burning. I also plan to run a gallon of Berryman b-12 in each tank, change the fuel/water separators and change the oil on both engines this weekend - you know, yearly stuff. But I appreciate other and advice or tips.

Thanks for the help!

 

[Skybolt]

Does your boat have the aft cabin? If so it's a Sundancer and not an EC. The EC's didn't have the aft cabin, but had the larger fuel tank(s) and the fresh water tank was in the middle of the boat under the stairs going forward. I had an 86' 340 with Crusaders in it. Was a great boat.

 

[Lazy Daze]

I've never seen a tank without an ID tag on it - always somewhere visible (relative term there!)... but I haven't seen everything, either Start by looking near the senders.

 

[Nater Potater]

Rochester Quadrajets are good carbs in my book. Their one Achilles heel is the main jet well plugs can begin to leak, allowing fuel to start leaking into the intake manifold. It usually manifests itself as a hard-start condition; hot start issues since fuel is dripping into a hot intake manifold causing an overly rich condition, or needing much throttle pumping after sitting for a few days due to the float bowl now being empty. I've resurrected a number of them with thoroughly cleaning and JB Welding the plugs. The prescribed method is more involved with some machining involved and adding o-ringed plugs, but I've never had to go to those measures. You can see it being done here:

There's the two large plugs for the secondaries you see in the foreground, then a number of smaller plugs in the standpipes between the smaller primaries. Search https://duckduckgo.com/?q=quadrajet+main+well+plug+repair&t=ftsa&atb=v184-1&ia=web for a real rabbit hole.

 

[J-Rides]

Does your boat have the aft cabin? If so it's a Sundancer and not an EC. The EC's didn't have the aft cabin, but had the larger fuel tank(s) and the fresh water tank was in the middle of the boat under the stairs going forward. I had an 86' 340 with Crusaders in it. Was a great boat.

No aft cabin, definitely the Express Cruiser. Thanks! It is a great boat!

 

[J-Rides]

Rochester Quadrajets are good carbs in my book. Their one Achilles heel is the main jet well plugs can begin to leak, allowing fuel to start leaking into the intake manifold. It usually manifests itself as a hard-start condition; hot start issues since fuel is dripping into a hot intake manifold causing an overly rich condition, or needing much throttle pumping after sitting for a few days due to the float bowl now being empty. I've resurrected a number of them with thoroughly cleaning and JB Welding the plugs. The prescribed method is more involved with some machining involved and adding o-ringed plugs, but I've never had to go to those measures. You can see it being done here:
View attachment 152269
There's the two large plugs for the secondaries you see in the foreground, then a number of smaller plugs in the standpipes between the smaller primaries. Search https://duckduckgo.com/?q=quadrajet+main+well+plug+repair&t=ftsa&atb=v184-1&ia=web for a real rabbit hole.

This is exactly what is happening right now. Hard starts, seems like I’m losing fuel, I just had no idea I’d be losing fuel that way. Gonna have to check that out. Tbh, I’ve toyed with the idea of putting Holley Sniper EFI on these engines anyways. Maybe it’s time

 

[Skybolt]

Rochester Quadrajets are good carbs in my book. Their one Achilles heel is the main jet well plugs can begin to leak, allowing fuel to start leaking into the intake manifold. It usually manifests itself as a hard-start condition; hot start issues since fuel is dripping into a hot intake manifold causing an overly rich condition, or needing much throttle pumping after sitting for a few days due to the float bowl now being empty. I've resurrected a number of them with thoroughly cleaning and JB Welding the plugs. The prescribed method is more involved with some machining involved and adding o-ringed plugs, but I've never had to go to those measures. You can see it being done here:
View attachment 152269
There's the two large plugs for the secondaries you see in the foreground, then a number of smaller plugs in the standpipes between the smaller primaries. Search https://duckduckgo.com/?q=quadrajet+main+well+plug+repair&t=ftsa&atb=v184-1&ia=web for a real rabbit hole.

And this is why I just replace the carbs with Edlebrock's. I have also JB welded them and it works for a time, but they always seem to loosen up and leak again. When the carbs are solid they are a good carburetor. Just have too many down sides when they age. JMO.

 

[J-Rides]

I've never seen a tank without an ID tag on it - always somewhere visible (relative term there!)... but I haven't seen everything, either Start by looking near the senders.

Good call - I'll check that out.

 

[J-Rides]

Rochester Quadrajets are good carbs in my book. Their one Achilles heel is the main jet well plugs can begin to leak, allowing fuel to start leaking into the intake manifold. It usually manifests itself as a hard-start condition; hot start issues since fuel is dripping into a hot intake manifold causing an overly rich condition, or needing much throttle pumping after sitting for a few days due to the float bowl now being empty. I've resurrected a number of them with thoroughly cleaning and JB Welding the plugs. The prescribed method is more involved with some machining involved and adding o-ringed plugs, but I've never had to go to those measures. You can see it being done here:
View attachment 152269
There's the two large plugs for the secondaries you see in the foreground, then a number of smaller plugs in the standpipes between the smaller primaries. Search https://duckduckgo.com/?q=quadrajet+main+well+plug+repair&t=ftsa&atb=v184-1&ia=web for a real rabbit hole.

Do you know what cfm the stock carbs are by chance?

 

[J-Rides]

And this is why I just replace the carbs with Edlebrock's. I have also JB welded them and it works for a time, but they always seem to loosen up and leak again. When the carbs are solid they are a good carburetor. Just have too many down sides when they age. JMO.

Any idea what CFM the originals were? Is an adapter plate needed to bolt on the intake?

 

[Skybolt]

Any idea what CFM the originals were? Is an adapter plate needed to bolt on the intake?

Most if not all of those quads's were 750. But yes an adapter plate is needed. The quad's are spread bore and the Edelbrock is square bore.

Adapter:

Carb Adapter #2696 Square-Bore Carb to Stock QuadraJet & Thermo-Quad 0.85 in.

Edelbrock Square-bore Carb to Spread-bore Manifold Adapter. #2696 is emissions legal when used with carburetor #1400 on a 1980 and older non-feedback GM vehicles powered by a V8 gasoline engine. EO D-215-10.

www.edelbrock.com

Carb:

Marine Carb #1410 750 CFM With Electric Choke, Zinc-Dichromate Finish (Non-EGR)

Edelbrock Marine Series 750 cfm, Square-Flange, Electric Choke Carburetor (non-EGR)

www.edelbrock.com

 

[J-Rides]

Most if not all of those quads's were 750. But yes an adapter plate is needed. The quad's are spread bore and the Edelbrock is square bore.

Adapter:

Carb Adapter #2696 Square-Bore Carb to Stock QuadraJet & Thermo-Quad 0.85 in.

Edelbrock Square-bore Carb to Spread-bore Manifold Adapter. #2696 is emissions legal when used with carburetor #1400 on a 1980 and older non-feedback GM vehicles powered by a V8 gasoline engine. EO D-215-10.

www.edelbrock.com

Carb:

Marine Carb #1410 750 CFM With Electric Choke, Zinc-Dichromate Finish (Non-EGR)

Edelbrock Marine Series 750 cfm, Square-Flange, Electric Choke Carburetor (non-EGR)

www.edelbrock.com

Hey thanks for the links and info. Now, I've heard that Edelbrock carbs are way more difficult to work on that Holley carbs. Any truth to that?

 

[Skybolt]

Hey thanks for the links and info. Now, I've heard that Edelbrock carbs are way more difficult to work on that Holley carbs. Any truth to that?

Not form my experience. There on par with the Qudrajet. Holly's are simple but tend to not last and are not a marine carb (even the marine version IMO). That dam power valve that pops on every backfire is tough to get past. For me they belong on cars. Cold big blocks tend to pop a bit at times. Would hate for that to mean I need to replace the power valve because of a cold engine. JMO.

 

[J-Rides]

Not form my experience. There on par with the Qudrajet. Holly's are simple but tend to not last and are not a marine carb (even the marine version IMO). That dam power valve that pops on every backfire is tough to get past. For me they belong on cars. Cold big blocks tend to pop a bit at times. Would hate for that to mean I need to replace the power valve because of a cold engine. JMO.

That's good to know. No matter what, it's all gonna be learning for me - holley or edlebrock. At this point no one has recommended anything else so we'll see. Thanks again for all the help. If I decide to go with one or the other I'll let you know.

 

[Skybolt]

That's good to know. No matter what, it's all gonna be learning for me - holley or edlebrock. At this point no one has recommended anything else so we'll see. Thanks again for all the help. If I decide to go with one or the other I'll let you know.

The marine Holly cost's more then the Edelbrock and you still need an adapter. Not by much though.

Adapter:

Mr. Gasket 1932 Mr. Gasket Carb Adapter - Open Center

The Mr. Gasket Carburetor Adapter Kit allows you to install a square flange carburetor like a Holley 4150,4160, Edelbrock, Carter AFB, etcetera,, onto a Quadra-jet or Thermoquad 4-barrel spreadbore intake manifold. And yes, it works in reverse. Just flip it over, and it allows you to install a...

www.holley.com

Carb:

Holley 0-9015-2 750 CFM Marine Carburetor

All Holley Marine Carburetors are designed to meet Coast Guard specifications. A marine carburetors fuel metering system is calibrated to compensate for unique engine loads found on boats. The J-style vent tubes direct fuel/fumes back into the carburetor for safe operation while on rough...

www.holley.com

 

[J-Rides]

The marine Holly cost's more then the Edelbrock and you still need an adapter. Not by much though.

Adapter:

Mr. Gasket 1932 Mr. Gasket Carb Adapter - Open Center

The Mr. Gasket Carburetor Adapter Kit allows you to install a square flange carburetor like a Holley 4150,4160, Edelbrock, Carter AFB, etcetera,, onto a Quadra-jet or Thermoquad 4-barrel spreadbore intake manifold. And yes, it works in reverse. Just flip it over, and it allows you to install a...

www.holley.com

Carb:

Holley 0-9015-2 750 CFM Marine Carburetor

All Holley Marine Carburetors are designed to meet Coast Guard specifications. A marine carburetors fuel metering system is calibrated to compensate for unique engine loads found on boats. The J-style vent tubes direct fuel/fumes back into the carburetor for safe operation while on rough...

www.holley.com

By the way, your boat looks amazing!

 

[Skybolt]

By the way, your boat looks amazing!

Thank you, I went much newer after my 86' and went for an 88'

 

[J-Rides]

The marine Holly cost's more then the Edelbrock and you still need an adapter. Not by much though.

Adapter:

Mr. Gasket 1932 Mr. Gasket Carb Adapter - Open Center

The Mr. Gasket Carburetor Adapter Kit allows you to install a square flange carburetor like a Holley 4150,4160, Edelbrock, Carter AFB, etcetera,, onto a Quadra-jet or Thermoquad 4-barrel spreadbore intake manifold. And yes, it works in reverse. Just flip it over, and it allows you to install a...

www.holley.com

Carb:

Holley 0-9015-2 750 CFM Marine Carburetor

All Holley Marine Carburetors are designed to meet Coast Guard specifications. A marine carburetors fuel metering system is calibrated to compensate for unique engine loads found on boats. The J-style vent tubes direct fuel/fumes back into the carburetor for safe operation while on rough...

www.holley.com

I also want to ask, besides the adapter and the carb itself, what else will I need to get to make this all work? Or is this mostly going to be a plug and play type situation. Specifically, do I need a regulator of some kind? Different jets? different spark arrestor (currently have an aftermarket K&N arrestor).

 

[Skybolt]

I also want to ask, besides the adapter and the carb itself, what else will I need to get to make this all work? Or is this mostly going to be a plug and play type situation. Specifically, do I need a regulator of some kind? Different jets? different spark arrestor (currently have an aftermarket K&N arrestor).

So those are good questions. You do need to have a USCG rated spark arrestor. Not sure the K&N qualifies for that, but some do. You would have to look that one up. The standard jets on the Edelbrock 750 are more then sufficient. If your fuel pump is stock then your good there as well. The Edelbrock/Holley throttle linkage is different then the Quadrajet. Be prepared to possibly make an adapter, shorten or lengthen the cable attachment. Fuel line may not line up exactly either. I think the Edelbrock is a very close match to the marine 4MV.

 

[Lazy Daze]

Concerning the spark arrestor - the key is to have a wire mesh. Newer Mercs do have a K&N style filter material used in there arrestors (I have no idea who actually makes it), but they also have the screen mesh.

Fun little project... if you have a piece of metal window screen laying around, hold it horizontally and hold a flame underneath it (butane match stick, for example)... it won't go through the metal screen! It's kinda cool to see that