Marine carb vs. Automotive carb.

6

69GTOby

Seaman Apprentice
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Alright, this is a very interesting topic to me. As my 350 MerC needs a carb (leaky Q Jet), I have been delving into this topic and received many mixed signals. Some say don't dare put an auto carb in a boat, some say it's the same thing just richen it up. I understand boats are under vastly different loads than cars. It would be like a car going up hill all the time.

I have a good 650 Holley spreadbore (4175 Q Jet replacement carb.). I emailed Holley Tech, asked for a carb recommendation, and asked if I could convert my 4175 for marine usage. He basically said boats need to be much richer, you can replace the jets, pump cam, power valve, etc... but it still will not be the same b/c the channels and metering plates are different. His recommendation was a 4175 "marine" carb. Which looks identical to my 4175 but has the J tubes, and a huge price tag. Even the specs for the squiter, pump cam, jets were the same.

Anyway, my boat is small, only 19.5', fairly light, and has a shallow V-hull. It's not a cruiser struggling to get on plane. It really seems to me like I could put my 4175 "auto" carb in the boat, richen it up as needed, make some J tubes for the float overflows... is that reasonable?
 
Bondo

Bondo

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Re: Marine carb vs. Automotive carb.

Ayuh,... Marine carbs are Marine for the same reasons Marine fuel pumps are Marine....

Any, 'n All potential spillage of fuel MUST be directed down the throttle bores, 'n not allowed Outside of the motor's in-coming induction air stream...

So,... You can do whatever ya want with yer Holley, so long as it's played with in a Marine sorta fashion... ;)
 
6

69GTOby

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Re: Marine carb vs. Automotive carb.

I looked over that thread, thank you.

For what it is worth, this auto Holley carb is probably much better, and safer than the leaky Q Jet that was on there. I can richen up the Holley to make it more suitable, and I can make some J tubes out of brake line or something.
 
etracer68

etracer68

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Re: Marine carb vs. Automotive carb.

We used to run a hose from the one vent tube to the other, with a cut out under the middle. If the float would stick open, the fuel would pour into the middle of the carb. You will have to make sure the flame arrestor fits too, dont run it without one. The other thing I would do is make sure you replace the accelerator pumps, as they are under the float bowls, and if they leak, they will leak on the outside of the carb. Im not real sure about the spread bore holleys though. As far as running lean, the auto carbs are set up that way because of the pollution, so you may need to fatten it up some. Holleys are very basic carbs, and very easy to work on. I have heard other people likeing the edelbrock carbs for marine use too. Im sure there will be other opinons, and I may have missed something too. Goodluck.
 
thumpar

thumpar

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Re: Marine carb vs. Automotive carb.

Why would you risk yours and others lives on a few dollars?
 
Tahorover

Tahorover

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Re: Marine carb vs. Automotive carb.

69GTOby said:
I looked over that thread, thank you.

For what it is worth, this auto Holley carb is probably much better, and safer than the leaky Q Jet that was on there. I can richen up the Holley to make it more suitable, and I can make some J tubes out of brake line or something.
Click to expand...

So you just want to patch it and not fix it? Your insurance will be void and your boat will be a danger to all aboard.
So how do you plan to fix the typical mid range (2000-3000 RPM) flat spot that most boaters experience with a auto carb?

5594138279_196b8ff158.jpg
 
J

JOEP2

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Re: Marine carb vs. Automotive carb.

I recently had the same delema, I had a q jet that was just leaky and worn out, so I took a edelbrock carb (same a the webber) and did all the mods to it to make it the same as a webber 4 barrel that's installed on boats, also called edlbrock about doing this and they advised me of the jets to use, the off road mod for the floats and that was all I had to change, other then the vacume springs above the needles, I do still run the fire arrestor air cleaner. Boat runs awsome so far. I was also told other then the color of the carb and the jetting there the same from edlbrock auto as the marine. Im not saying this is right but Im also wonder if this is going to be ok.
 
achris

achris

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Re: Marine carb vs. Automotive carb.

JOEP2 said:
I.... I was also told other then the color of the carb and the jetting there the same from edlbrock auto as the marine. Im not saying this is right but Im also wonder if this is going to be ok.
Click to expand...

That is definitely not right. There are a few quite subtle, but very significant differences. Not the less of which is the internal venting of the float chamber. Also the accelerator pump discharge volume, no vacuum advance port... Jetting is quite different also...

In short, if it's not a 'Marine' carburettor, don't use it in a marine environment... (same goes for electrical items too)

Chris...........
 
series60

series60

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Re: Marine carb vs. Automotive carb.

I'd be glad to take all those old Marine Q-jets off any ones hands
 
L

lamphega

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Re: Marine carb vs. Automotive carb.

Send your old marine carb to a professional rebuild shop. I did this with my 2GC Rochester that leaked near the throttle rod. They did a great job and I don't worry about a thing.
 
etracer68

etracer68

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Re: Marine carb vs. Automotive carb.

Now, thats a cool picture. And I mean the colors.

I have a few Qjets under my work bench, that I use for parts, if someones boat that I may work on. I have never been a fan of Qjets.
 
Bondo

Bondo

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Re: Marine carb vs. Automotive carb.

JOEP2 said:
I recently had the same delema, I had a q jet that was just leaky and worn out, so I took a edelbrock carb (same a the webber) and did all the mods to it to make it the same as a webber 4 barrel that's installed on boats, also called edlbrock about doing this and they advised me of the jets to use, the off road mod for the floats and that was all I had to change, other then the vacume springs above the needles, I do still run the fire arrestor air cleaner. Boat runs awsome so far. I was also told other then the color of the carb and the jetting there the same from edlbrock auto as the marine. Im not saying this is right but Im also wonder if this is going to be ok.
Click to expand...

Ayuh,... The Carter Clone carbs,... I Love 'em....
The Edlebrock Street/ Strip Kit is a Must Have item...
The Edlebrock parts fit the Merc/ Weber, perfectly, 'n are cheaper, 'n Much easier to find...

The fact that Edlebrock gives 'em different part numbers than their street versions, tells Me, their not the Exact same...
Though I've never had the 2 versions side by side, much less apart...

I actually Hated mine, til I figured out the Edlebrock parts fit it...
The fumes at the stern were terrible, 'n I could get the Merc dealers to find bigger needles or nothin'....
After playin' with it 6 ways to sunday, I Love it,...
It sips gas, 'n will rip yer head off when hammered...


Once ya get past the 1st start of the day, anyways,.... ;)
 
riskibusiness

riskibusiness

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Re: Marine carb vs. Automotive carb.

My local omc dealer sells rebuild kits for the mercruiser 2-jet thats on my 3.7. And carbs are really easy to rebuild. As long as the throttle shaft bushings arent bad I would just rebuild what you have. Alot cheaper than a new one. And way cheaper than a new boat when yours goes blewy.
 
cr2k

cr2k

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Re: Marine carb vs. Automotive carb.

A 2GC and a Mercarb have nothing in common with a Q-Jet.
 
6

69GTOby

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Messages
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Re: Marine carb vs. Automotive carb.

The 2GC is a 2bbl by Rochester, and the Q Jet is a vastly different vac sec 4bbl by Rochester... Right?
"Darwin's work is never done!" Hardy har harr. I am trying to have a fruitful conversation about the differences of auto vs. marine carbs and conversion possibilities. I have had some good feedback, so thank you to those. I understand there are differences, most importantly safety related. I can make some J tubes, or a crossover of the float bowls with a drip hole as someone suggested. I can jet it up and install a steeper pump cam, other than that, I think it should work well and safely. Am I missing anything?
 
6

69GTOby

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Messages
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Re: Marine carb vs. Automotive carb.

Many of you will be pleased to know that I have decided to rebuild the original Q jet. Websters wanted 200 some bucks to rebuild it, which is way high, IMO. For that much, I can take a stab at rebuilding it myself, and if something went wrong, I could still pay someone to rebuild it and not spend that much. Does anyone know a good place to get a rebuild kit, and which one I will need?
 
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