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marinize a quadrajet?

FstaRockr Burns

FstaRockr Burns

Regular Contributor
So far - add jtube from vent down primaries, drill hole in float body for mech pump over flow hose, and obviously a flame arrestor - Remove everything except elec choke and vac pull off for the secondaries.

anything else come to mind?
 
Idle screw cam must be round with NO steps for automotive high idle. If you dont do this, when engine is cold it will idle above 1200 rpm.

ALL Vacuum ports must be closed off. if possible I would suggest drill, thread, plug and use JB weld on threads of plug. File clean and flat when done.

Primary and secondary jets should be checked against mercruiser manual for correct size.
Primary and secondary metering rods and secondary hanger cam must be to mercruiser specifications per manual.

If you say what year/engine size we can upload jet, metering rod and cam size charts also where to ass sight tube fitting
 
FstaRockr Burns said:
So far - add jtube from vent down primaries, drill hole in float body for mech pump over flow hose, and obviously a flame arrestor - Remove everything except elec choke and vac pull off for the secondaries.

anything else come to mind?
Click to expand...

MArine carbs have an ID on them indicating that they are marine... That's what anyone who inspects your boat would be looking for.... including the insurance co in the event of a claim.
 
tx jack - i did find some numbers for a 383.. which is what im working on now (converting from volvo penta to a carb).. unless theres a way to reprogram the vp ecu for a 383 which i doubt..

is there a marine specific sheet with rod/jet combos? i presumed one would use the automotive charts.. i do have a wideband as well if need be but i can usually tune them pretty darn good by smell and sound..
 
FstaRockr Burns said:
So far - add jtube from vent down primaries, drill hole in float body for mech pump over flow hose, and obviously a flame arrestor - Remove everything except elec choke and vac pull off for the secondaries.

anything else come to mind?
Click to expand...

MArine carbs have an ID on them indicating that they are marine... That's what anyone who inspects your boat would be looking for.... including the insurance co in the event of a claim.
 
If your not needing the ecm and its a TBI injected motor your converting I need a ecm from a V8 TBI
PM me about it.
 
How old is this thing? I'm not 100 percent certain that the existing FI won't work on the slightly larger displacement, esp if it's TBI.
 
FstaRockr Burns said:
tx jack - i did find some numbers for a 383.. which is what im working on now (converting from volvo penta to a carb).. unless theres a way to reprogram the vp ecu for a 383 which i doubt..

is there a marine specific sheet with rod/jet combos? i presumed one would use the automotive charts.. i do have a wideband as well if need be but i can usually tune them pretty darn good by smell and sound..
Click to expand...

Need more info

What boat? length and approx weight?

Approx horse power and torque.

If under 300 hp I would say the same as a 350 mag calibration.

if higher like 325-350 then a 454 calibration.

Not a whole lot of difference and Mikes carbs I think has metering rods and other tuning parts
 
Unless I'm wrong (hah!) the float camber vents on a marine carb are designed to make it flood INTO the carb.

Jeff
 
fastjeff said:
Unless I'm wrong (hah!) the float camber vents on a marine carb are designed to make it flood INTO the carb.

Jeff
Click to expand...

The vent tubes on the Rochester 4 bbl are a few styles.

Automotive are straight tubes and can extend rather high. May or may not have 45* cut on one of the tubes

Marine are shorter and some have a 45* angle cut pointing inwards so FUMES get sucked into throttle body. The shorter tubes may be because of the low hieght of the flame arrestor.

There are some Rochester 4bbl with J tubes but I have never seen an OEM Mercruiser with them not to say they dont exist but they are rare

Holley Marine 4 bbl typically have the J tubes on the primary and secondary. Makes it easy to pick up and carry!!

The VENT tubes are not related to flooding although if it were to flood they certainly could direct fuel into throttle body but that is not their primary function



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If you are using an electric fuel pump you don’t need the nipple for the fuel pump overflow hosp, that is only needed if are using a mechanical pump as was used on the pre Vortec engines. Since this engine had EFI it must have come with the electric pump. For the carb conversion you need a low pressure electric pump wired so it cuts off if the engine stalls (safety feature). I have an original marine QJet on my 1988 4.3 and it has the short vent cut at a 45* angle and the nipple for the overflow hose for the mechanical pump. If you are using this on a Vortec engine the choke has to be converted to electric.
 
going down that path will get you more liability than most willingly sign up for...

You'd be much better off remapping the ECU, especially if it drives the ignition system.
 
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