General Category > Quadrajet Carb Talk and Tips

carb questions

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old blue 75:
Hey guys I have a carb i'm working on and need some info on it.
The number is 17059288. In the book there is no 88.
 From what i can tell it is from a boat. It has the look of a 1975 and older(chevy side in let.) but has
a 1979 date. There is no pcv valve port on the front, divorced choke.
Being a 1979 will this have a apt or not?
 I would like to add the port for the pcv, it has a flat spot for it so i'm thinking of tapping it for
1/8" npt for a nipple. I work in a machine shop so adding the npt hole is no big deal.

Kenth:
You´ve got a 4MV Quadrajet for Marine usage.
No vacuum ports or APT. Fuel overflow tube from "passenger" side primary venturi.
Better left for the seaside guys.

old cars:
Kenth. Is this the tube your referring to. Could you explain how that works? And did all marine quadrajets  use this? Thanks

Kenth:
Marine pumps have a double diaphragm. When the first one breaks, it will leak fuel into the cavity where the small hose port is and send it to the carburetor instead of the bilge.
Also, marine units rarely, if ever, use fast idle cams.

Cliff Ruggles:
Marine Q-jets come in two flavors, Volvo Penta and basically everything else.  With that said there are a few exceptions to that rule as Q-jets were used on some rare 4 cylinder Ford Marine engines and "odd" applications in very late years of production.  So you may on occasion run into a Marine unit that is side inlet (Chevy style) but also electric choke.

Volvo Penta units were built from Oldsmobile style (early) hot air units, many are electric choke.

OMC, Mercruiser, Crusader, etc will be Chevy style side inlet units with divorced chokes.

Most Marine units did not use PCV or vacuum advance, or fast idle parts but the cams are often in place just not parts on the primary shaft.  They may have done this just for the weight to help with divorced choke operation.

In any case I do not recommend using a Marine carburetor for automotive and truck use.  They have special calibrations and castings because Marine engines were heavily loaded most of their lives.  They aren't emission calibrated either, so pretty generous for fuel delivery.

Marine carburetors also take different rebuild parts, which are NOT supplied in currently available rebuild kits unless you get them here.

I rebuild hundreds of Marine units and well known for doing them.  In the last 20 years it is rare to see one show up here with the correct N/S assembly and accl pump.  Even if they have the short pump in them it will use the "soft" blue seal and have already failed or failing as they are not compatible with this new fuel.

So basically Marine Q-jets REQUIRE high flow N/S assemblies to keep them bowl under heavy load and high RPM's.  The accl pumps are short for a reason.  If you are cruising on a plain enough throttle is used up there will be little or no pump shot left if you move the Morse controls ahead to speed up.  Without some pump shot in that scenario you may experience a stumble or bog due to a momentary lean condition.

So outfitting Marine units with automotive parts, or the wrong parts is a recipe for disaster before you even get started.  Hope this helps some......Cliff

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