carburetor question please advise

[Jestertattoo]

i have a rebuilt 1997 5.7 OMC. it have is a rochester quadrajet 17800563. that is dumping to much fuel into the manifold. I researched and found that this model of carb is for a 7.4 454. the manifold is also not factory. it has somewhat of a higher rise to it. does any of this matter, will what i have work with the proper adjustments, or do i need the correct carb for the 350?

 

[Scott Danforth]

welcome aboard

the carb is most likely fine for the application, except for dumping the fuel

most likely its the welsh plugs leaking (common issue on rochester carbs)

however it could be stuck float (another issue) or it could be the fuel pump died and is pumping fuel up the clear hose to the spark arrestor

so if the fuel isnt in the clear hose, your carb need an overhaul

 

[kenny nunez]

You do not have the correct marine carburetor. I looked up the marine application chart and from what #s I could get your carburetor is for a manual transmission vehicle. The jetting,metering rods, and power valve spring is actually letting too much fuel because of the vacuum signal. This is a common symptom with an auto carburetor on a marine engine. Also the genuine Q Jets for marine applications usually have an extra port in the front for the fuel pump safety line should the pump start leaking. Some time there is no port and there is a bracket holding the safety line facing into the air horn.
Summit or Jegs have the correct carburetors in stock. They also have the Edelbrock marine versions. With the correct carburetor you will see a difference in consumption and all around performance.

 

[Jestertattoo]

apparently i have the numbers mixed up my apologies!!! the correct numbers are 17080563

 

[Lou C]

By 1997 OMC and Volvo were not using Quadrajet carbs any longer, they seemed to have switched to Holley carbs around 1990 or so. After looking through the BRP OMC sterndrive catalogs, what they appear to have been using is a Holley 4175 spread bore carb that does not need an adapter on the stock GM spread bore cast iron manifold. What manifold do you have in the first place? If it is a square bore intake the Q-Jet will not work, you will need to use a Holley or Edelbrock. Post up some pix of what you have....

 

[Jestertattoo]

[No message]

 

[kenny nunez]

You do in fact have a marine carburetor if the # you posted is 17080563. I looked it up on Flying Fish Carburetors web site. It is listed as a Mercruiser carburetor. They can rebuild your carburetor or could set you up with a square bore Holley that would probably work better with the manifold. I suggest you contact them and explain what you have and hopefully they can help you.
It appears you have a square bore manifold . Is there room for the secondary butterfly’s to open?

 

[Jestertattoo]

Yes i have a spacer that i can in between

 

[kenny nunez]

What type of spacer, does it divide the front from the back barrels? If it is open in the middle you will get a “reversion” which will hurt low to mid range torque. How much vacuum is there at idle?

 

[Jestertattoo]

There is my issue!! It is open in the middle!! And it is dumping way to much fuel! Black smoke!! Believing this carb is completely wrong and in need of rebuild

 

[kenny nunez]

Do you have any idea if the engine has the original cam? With a marine engine idling on a flush out the vacuum will be around 14-16. While idling in the water may be only around 5-7 because of the back pressure. That manifold will work better with a square bore style carburetor. Do you know any history of the carburetor you have, was it “improved” by the previous owner? If so then you really need to get another carburetor.

 

[Jestertattoo]

It has a different cam!! They were trying to get more bottom end torque and carb is off of a 454

 

[Lou C]

What I would do is try to get the specs of the cam, and call Holley tech support, see if they think they have a carb that will work with your engine or can be easily tweaked to work with it. Holleys are easily modified to suit individual engines if the owner is able to do what is suggested, or can have a shop do it. I don't think you could ever get a Q-Jet to work on that square bore manifold, that is for either a Holley or Edelbrock carb.

 

[kenny nunez]

On page 26 of the latest Summit catalog there is an adapter, #edl2606 which says it is to mount a square bore carburetor to a Q jet manifold, It may work in reverse. Or switch to a Performer series on page 22.
It would be helpful if you could find out which cam is in the engine. With the correct cam/manifold/ carburetor I am sure the engine will do much better.

 

[jimmbo]

If you have a square bore manifold, use a square bore carb. If you have a spreadbore manifold use a Spreadbore carb. I have yet to see a good adapter, the best one so far, was open between the primaries and secondaries, but divided port and starboard. It will extend the plenum a bit, but that shouldn't matter much. The adapters that have four separate holes that taper to match, are really bad. Volvo makes a real good 4bbl intake for the Vortec engines that fits both types of carbs, and with a plate adapter, Volvo used it with the 2bbl Holleys.

 

[Lou C]

I wondered about this as well when I was doing my Q-Jet to Holley 4bbl conversion. On the OMC/Volvo 4.3s OMC and later Volvo switched from the Q-Jet to the Holley 4160 around 1990 or so. They used an adapter plate that is similar to what is sold by Mr Gasket, Holley and Edelbrock (open in the center, no divider). The only real difference between the aftermarket ones and the OE OMC/Volvo one is that the OE style is 1/2" tall vs the others are 3/4" tall. I was able to get the OE OMC/Volvo plate, it fits a bit better than the Mr. Gasket one I tried first and the hardware is much better. However, I have never seen an adapter plate for these spread bore manifolds with a divider. Only the open style and the one with the 4 holes (Edelbrock). I would have used a square bore manifold but for this pre-vortec engine there are not many choices and the Edelbrock style that fits this engine does not work with the high mounted alternator on the OMC/Volvo rigged engines (the water outlet is too far over, not centered like the OE manifold).
I looked into using the spread bore Holley 4175 (this was used on OMC/Volvo V8 applications) but it is too long to fit because of the different fuel inlet on the front bowl (would interfere with the thermostat housing). I would have had to use a tall spacer to make this work. Since the OE installation used the 1/2" plate with the 4160 that's what I did.....

 

[Jestertattoo]

The adapter plate is open, does not divide all it does is add 1/2” spacer and bolt hole pattern!!