Marine QJ Choice

[zkurtb]

I have two marine QJs available to choose from and would appreciate any thoughts on which would be the better choice to use on my 1987 I/O boat with chevy 5.7L and electronic ignition, already set up for a QJ.  I want to replace current carb because  top plate is warpped - I don't want to deal with fixing that and I can get either of the others for a pretty good price.

One is a 17059286 which I believe is 1979, 49 state emissions; it has secondary rod hanger "B".  It came off a boat with a chevy 5.0L OMC  I/O.

Other is a 17080561 which I believe is a 1980, California and high altitude; it has secondary rod hanger is "J". It came off a chevy 5.7L Mercruiser I/O.

I have not had them apart so don't know what jets or primary metering rods and power piston spring they have.  All the boats are in the same 2800 lbs weight range.

Granted, the second one is already off a 5.7L, so it might be tempting to assume it would be the better choice to go on my 5.7L, but perhaps not necessarily...hence why I am posting. I'm particularly interested in thoughts on the tradeoffs and differences between the 49-state and California versions. I'm wondering whether the 1980 California/high-altitude one might be less in performance since it's emissions oriented.  But on the other hand, I'd prefer better gas-knottage over absolute max horespower.  Our altitude is 2500'.

All thoughts welcome.

[makomark]

I don't think you will find anything hugely different between them.....The decoded numbers don't always have an accurate translation for the marine applications.

I'd be more inclined to evaluate each one for its physical condition and select the one in the best shape. Pay particular attention to the screws and their threads - also, the condition of the primary throttle plates can give you some insight into their previous use.

Jets, rods, and hangers can be changed as needed.

Good Luck

[zkurtb]

Thanks Makomark, great points. 

I was hoping to use them out-of-the-box, so to speak, without a lot of performance tuning via experimenting with power-piston springs and jets and rods, etc. 

Anyone have thought on which might be best "as is"?

[Cliff Ruggles]

Marine units are pretty generous for fuel delivery right to start with.  Seldom is it necessary to increase jet size with them, and they typically have a lot of idle fuel available as well.  The best course of action would be to completely/correctly rebuild one of the units and test it in all areas, then go back and address any areas that need help.

We sell complete rebuild kits for Marine units, with upgraded parts for modern fuels.....Cliff

[Cliff Ruggles]

Just a side note on Marine Q-jets.  I rebuilt one last week that was on a mid 80's big block Chevy Marine unit.  Wanting to get my Ventura out for some street driving I decided to install the Marine unit on the car for testing.

I put about 20 miles on it, and it ran FLAWLESSLY in all areas.  I made half a dozen full throttle runs thru all the gears with it, and it never faltered once.  This was with the stock jetting and metering rods.  The only mods to it were internal venting, and a larger .145" fuel inlet seat.  The owner was complaining of running the carb dry on his boat under full throttle......Cliff