Should Carb. settings be the same for a 350 and 350 Magnum engine?

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I have a 1984 Mercruiser 5.7L 260hp V8. The Rochester quadrajet (17090210) that had run for years on it finally needed replacing. I purchased a re-build that was advertised as being a replacement that was built and calibrated for the Rochester Quad 17090210. Felt great, then I noticed seller advertised as being built and calibrated for the Mercruiser 350 Magnum engine as well. I don't have a Magnum. The carb arrived and looked almost identical, intalled easily and it started right up but it ran terrible, rough, jerky and I had to use the throttle to keep it going between 1600 and 2000rpm. It wouldn't run on it's own or smooth out so I shut it down. It seems to me the jets, settings or something would have to be different for the higher HP Magnum engine than the standard or is there something I need to do or adjust or ...

The difference between the two would not cause the issues you are experiencing.

The difference between the two is the secondary hanger cam and needles which would in your case possibly cause a rich condition at higher speeds.

Most likely it wouldnt be noticed.

can you return the carb?

Sounds like something is wrong with the rebuild.

No they don't allow returns. I took the cover off and started it up this morning and you could hear the leaks a block away. I took it off and found the two screws that mount the base to the body were not much more than finger tight. Also what looked like a 1/4" breach in the gasket between the same two sections. Turned out to be a soft spot in the gasket that may or may not have contributed. Just going to check everything holding this together and re-mount it with a new base gasket with a bead of sealer. Torque it 20lbs and pray. Thank you for your help kghost.

Fix any vacum leaks , set the idle mixture and speed. Have you set your ignition timing as well?

Any other trouble shooting done ?------It is not always the carburetor that is in need of replacing !

I'll bet that repairing that gasket does the trick.
This is just my 2 cents but I don't trust "rebuilt" carbs from anyone except the original manufacturer and it has to have a warranty. Burned too many times.

o2batsea said:

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This is just my 2 cents but I don't trust "rebuilt" carbs ...

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2X that one. your best bet is to have a real pro rebuild what you have...the 'reman houses' do things as economically as possible, not necessarily 'by the book'...

bingo. two plugs were dripping oil. one of the cyl at 30psi and it started smoking, badly.