Mercury XR6 150 2.5

[rock]

Because the porting is different on a 200 and putting 150 parts back on it wouldn’t work correctly?

It would probably run just not right or, depending on what parts you swapped, for very long. Motors are air pumps and they need to be balanced to be all they can be. By balanced I mean you need to be able to process what you put in. If you put on bigger carbs you need to have a less restrictive exhaust in order to process what you put in. Port sizes and locations can also restrict processing so back to the bigger carbs if you can't use what the bigger carb offers then you can actually take a step backwards and hinder performance by introducing more air and fuel. Most think bigger is better but only if all sides of the equation are addressed. 200 carbs on a 150 will likely produce less power than the 150 carbs did due to the inability of the porting and exhaust to process the extra air and fuel of the 200 carb.

Rock

[David - WI]

If you order one of those powerheads online, you would have to tell them which one you are replacing.

[bullet123]

If you blow a power head(rod through block) and put a new power head on, what have you put on? When advertised for sale on the internet they are listed as a 150, 175, 200. All being a 2.5. Now if you had 150 carbs and ignition and all to put back on it. It would be a 150? Same for a 175? And 200? I guess maybe I’m not understanding how it can be advertised at that if it wouldn’t work that way? Because the porting is different on a 200 and putting 150 parts back on it wouldn’t work correctly? Or would it? Just with restriction?

Tell us what you have now and what you want to end up with and im sure one of us can point you in the right direction. for instance....if you buy a bare 200 block (rotating assembly powerhead) to put on your 150 midsection, the only thing you will need to change is tuner and carbs. you can find them real cheap on this site.