Carb swap 305 to 350?

[CatriderF7]

Do I need to do anything special to change a 4bbl carb from a 1989 5.0 mercruiser to a 1999 5.7 mercruiser besides just change the intake with it?

 

[Bondo]

Do I need to do anything special to change a 4bbl carb from a 1989 5.0 mercruiser to a 1999 5.7 mercruiser besides just change the intake with it?

Ayuh,.... The intake from an '89, won't fit a '99 motor,...

The bolt pattern is different,.... the '99 only has 8 bolts, 'n the '89 has 12 bolts,...

 

[CatriderF7]

Ok thanks. Do you know if the carbs are interchangeable?

 

[harleyman1975]

The carbs should swap out as long as they look the same and have the same hook-ups and linkages. Just make sure that they are physically the same. Use new base gasket.

 

[CatriderF7]

Ok but as far as jetting they should be the same?

 

[NHGuy]

The 1989 5.7 uses .068 jets, .041 primary metering rods. Each is .001" smaller than the 5.0 uses. Secondary rods are the same. I'd try it the way it is before going through all that. I don't have the 1999 info here.
It might run fine the way it is. But if you will have it apart for any other reason, change them.
If you get a lean pop at part throttle that's lack of fuel, more likely the rods. A smaller rod allows more fuel through the opening. I don't get why the bigger motor uses a smaller jet though. My thinking is smaller jet = less gas.