03 Yam 60 to70hp conversion.

[joe brown]

What parts do I need to convert a 2003 Yamaha 60 two stroke to a 70 hp two stroke? I know the heads need to be changed. I also think the carbs and exhaust muffler need to be changed.
Another question I have is what is the deal with Yam showing two differant part numbers for carbs on the 60 and 70? Both part numbers are identical. Same for the exhaust. In reality is the fiche the same for both motors and one part# is for the 60 and the other the 70?

[boats.net]

The part numbers are different the 60 is a 6H2 part number and the 70 is 6H3 number. The only way to find all the parts is to compare the parts between the two engines.

[joe brown]

Thats exactly what I needed to know. It looks like the carbs and exhaust tuner are the only thing that is differant. Slap on a new set of carbs and a 70 tuner or one form hydro tec and you have a 60 that makes 70 or more HP!

[dtmackey]

Building one size block and having 2 or 3 horsepower ratings is a very common thing across all outboard manuafacturers. The information I am sharing is based on two stroke (not direct injected) but some aspects could also be applied to direct injected and 4-strokes. The 4 most common things between horsepower ratings of the same size block are:

1. Timing - this can be adjusted provided it is not electronically con*****ed.
2. Reed spacers - These can be added, but disassembly of the motor is required.
3. Exhaust tuning tube - Powerhead removal required - this is not for the shade tree mechanic.
4. Bigger jets (carb motors only) FI motors may have programming that adjusts for this.

These are the most common changes for extracting more power from similar motors. Manufacturers make this very difficult to understand by using different part numbers for the same thing when related to the same block. Image saving $1500 buy purchasing the lowest HP rating for an engine size and spending $200 in parts to turn it into something more powerful......


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