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Permalink Reply by Edward "Ed" STONE on May 22, 2013 at 8:09pm

There will be many replies to this; of that I am confident. If I learned it correctly, the most basic answer is that the item (I.e. carburetor, starter, etc.) or the materials are specifically designed and made to survive in a marine environment and / or keep the vessel operators safe while using it. A 327F motor automotive carburetor exhausts excess fuel which evaporates harmlessly as it falls to the roadway below the vehicle; a boat's 327F carburetor drains that surplus fuel back to the fuel pump,to be captured and recirculated into the fuel feed system, thereby preventing its potentially hazardous and explosive condition in the boats enclosed engine compartment or bilge area. Dick Morland, Lee Dahlen, or many others will echo or correct and accurize for the audience!

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Permalink Reply by Quentin on May 23, 2013 at 7:33am

That's a good article, but they left out one important fact: in addition to certain legitimate reasons why marine stuff costs more, they also frequently bump up the price just because it says "marine" or is sold in a chandlery instead of an auto parts store.

;-)

Q

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Permalink Reply by Dick Morland on May 24, 2013 at 11:29am

IMHO, there's no valid reason for the huge difference in price when an item becomes marine, even though there really are some differences. Marine carbs are a good example. If properly operating and jetted (no increase in price at the mfg. level), an automotive carb would work fine in a boat. The marine carb modifications are for keeping a malfunctioning carb from blowing up the boat ! Ed mentions "surplus fuel", which does not exist in a properly functioning carb, automotive or marine. Only a carb that has developed internal leaks has surplus fuel.

A marine carb has 2 main changes, venting the fuel bowls into the throat (or interior) of the carb, and tighter fitting throttle blade shafts so that if there is any internal fuel leakage after engine shutdown, the leakage does not migrate past the throttle shaft to the outside of the carb. Here's what Edelbrock says about their marine version of their Carter clone:

MARINE CARBURETORS 
For use in marine applications, these Edelbrock carbs comply with U.S. Coast Guard safety standards. Cast surfaces are iridited with PTFE-coated shafts and pump arm for maximum protection. Other features include modified bowl venting, specially designed throttle shafts, accelerator pump seal, 3/8" inverted flare fuel inlet fitting, tube in airhorn for fuel pump vent, 5-1/8" flame arrestor flange, universal throttle lever and revised secondaries for improved transient performance.

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There's a bunch of advertising BS in here, but note the two main things --- throttle shafts and bowl venting. The marine carb is $100 more than the almost identical automotive carb. I can guarantee you the automotive jobbie has the internal bowl venting just like the marine, so the main difference is the throttle shafts, and these do not cost the manufacturer more than 5 or 10 bucks per carb.

Ed mentioned " a boat's 327F carburetor drains that surplus fuel back to the fuel pump,to be captured and recirculated into the fuel feed system," ------ This is system employed on diesels and some automotive fuel injection systems, but certainly not the 327F fuel delivery system as designed by Chris Craft and Carter carburetors. There is a later fuel system addition, but this is a line from a replacement fuel pump port to either a non vacuum port on the carb, or a port added to the flame arrestor. This is designed to route any possible future internal fuel pump leakage right into the carb and then the engine. The original fuel pumps routed any leakage into the crankcase where fuel leakage would contaminate a and thin out the engine oil. The newer system merely dumps any leakage into a running engine. It certainly isn't properly metered, but it's better than going into the oil. It looks like it might be an excess fuel return, but that's not it's intent or purpose. There should never be anything in this line in a properly running marine engine. OK, stepping down from my soapbox now -----  :-) 

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Permalink Reply by Timothy "Tim" Miller on May 24, 2013 at 4:01pm

One other venting possibility was the fuel pump would send a mist into the engine bilge if the diaphragm failed.  This mist originates at the top of the pump near the hinge pin.  Found it out about 15 miles into the trip to Mecca for the rendezvous.  We did not hesitate to remedy this problem.

Tim

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Chief CommanderPermalink Reply by Mike H on January 12, 2021 at 7:09am

This is very basic, but gets the point across. 

This video by Teleflex elaborates on some of the key differences between a marine engine in comparison to an automotive. Although some automobile parts look exactly the same you will see in this video the hidden features that go into an aquatic engine making it efficient and safe for the marine environment.

https://commanderclub.com/video/marine-vs-auto

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Permalink Reply by Jim Frens on January 12, 2021 at 8:59am

Not to mention the cost of product liability insurance built into every product, marine or not. For marine products, it's bound to be much higher.

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