Proper Carb Size for 318

levelwind
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Proper Carb Size for 318

Postby levelwind » Thu Jun 01, 2017 12:13 pm

My 318's have Carter AFB 750 CFM carbs. I was told this by the number and the primaries are almost as big as the secondaries. I rebuilt the starboard and the port kit is on order. Considered upgrading to Edlebrock but which one 1409 is 650 CFM or 1410 is 700 CFM. Will I gain or lose fuel economy going down to 650 CFM? Some input would be helpful and appreciated.
Brian & Susan
"X-Rayz"
Upper Niagara River
1981 Marinette
28ft Sedan FB
Twin Chrylser 318's
Raw water cooled

Ray4713
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Re: Proper Carb Size for 318

Postby Ray4713 » Thu Jun 01, 2017 2:39 pm

There is quite a bit of info out there on sizing carbs. IMO you need to also consider air flow. What type of air filter / flame arrestor are you running?
1987 32' Sedan Flybridge "Brown Eyes"
Twin Chrysler 318s
Center Hill lake, TN

honestcharlie56
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Re: Proper Carb Size for 318

Postby honestcharlie56 » Thu Jun 01, 2017 3:29 pm

That 1410 is going to be too big for a 318, just my opinion....maybe I'm wrong. Small engine that never needs to run past 4500 rpm doesnt need a huge carb.
1990 Marinette 32 Sedan Flybridge "Hubba" Lake Charles, LA
Twin Chrysler 318's

Fastjeff
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Re: Proper Carb Size for 318

Postby Fastjeff » Thu Jun 01, 2017 4:10 pm

A two barrel carb is more than enough for most twin engine Marinettes.

A case in point: My old 32 footer (360s) would plane off at the SAME throttle setting needed to cruise at 2,500 rpm/ 18-20 mph. I marked the throttles where this was and did some measuring (with the engines off). The butterflies were open so little I could not stick a PENCIL in the openings! And this was with over sized props that limited WOT rpm to 3,900.

Jeff
"We live at the bottom of an ocean of air, not at the top." General Marvage Slatington

Tuggle
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Re: Proper Carb Size for 318

Postby Tuggle » Thu Jun 01, 2017 6:09 pm

Are those 750's stock? Mine are Carter 600's on 318's.
"Deplorable", 1975 32' Express, Twin 318's, Raw Water Cooled, Lake Lanier, Ga.

levelwind
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Re: Proper Carb Size for 318

Postby levelwind » Fri Jun 02, 2017 5:55 am

Not sure. That's why I'm inquiring. I am the 4th owner. The 3rd didn't replace them and he bought the in central OH. Going through some old receipts there seemed to be a lot of overpriced repairs done that I would have questioned. When I found an exact Carter rebuilt replacement on EBay, I contacted the seller Hemigeorge and he informed me that the 750 CFM was to big. So I passed on that one and bought another that needed rebuilt to practice on now I can't get one of the primary venturi's out of the float bowl even after heating it. More heat I guess?
Brian & Susan
"X-Rayz"
Upper Niagara River
1981 Marinette
28ft Sedan FB
Twin Chrylser 318's
Raw water cooled

Fastjeff
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Location: Rock Halll, MD
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Re: Proper Carb Size for 318

Postby Fastjeff » Fri Jun 02, 2017 6:47 am

A word of caution on reusing those old Carter AFBs: I HAD to toss two of them out after ethanol gas caused porosity that made them leak, right through the carb body. I rebuilt them with new parts several times, thinking the needle and seats were leaking, but no. Ended up buying Edelbrock 1409s.

Jeff
"We live at the bottom of an ocean of air, not at the top." General Marvage Slatington

Tuggle
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Re: Proper Carb Size for 318

Postby Tuggle » Fri Jun 02, 2017 9:52 am

Did have my Carter's rebuilt supposedly to a "better than new" standard, per the cost, and not much cheaper than new Edelbrocks, I've often wondered if buying new wasn't the way to go. As a matter of principal I always try to stay with original equipment.
"Deplorable", 1975 32' Express, Twin 318's, Raw Water Cooled, Lake Lanier, Ga.

jmonday
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Re: Proper Carb Size for 318

Postby jmonday » Fri Jun 02, 2017 2:12 pm

I have the 1409 on mine.
Jeff Monday (Blue Mondays)
1973 28 ft Express single 318 1976 StarCraft Islander 1961 Sea Nymph
Lower River rd
Rabbit Hash KY

honestcharlie56
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Re: Proper Carb Size for 318

Postby honestcharlie56 » Fri Jun 02, 2017 2:20 pm

Not sure on yours, but alot of carbs are coated internally. Once this is worn off they can start to rot away. I'm pretty sure the quadrajets were, like I said not to sure about yours.
1990 Marinette 32 Sedan Flybridge "Hubba" Lake Charles, LA
Twin Chrysler 318's