Originally Posted by Searider
Friend of mine has told me he's just about to buy a new yamaha 6hp. Looking at the spec it looks as if the 4, 5 and 6hp are based on the same capacity block. Same max rom range. Same gear ratio.
Anyone know what's different between them? Can a 4 be modified into a 5 or a 6?
This isn't unusual, the Tohatsu 60C is the same block as a 70C. Yamaha 40hp (40V) uses the same block as (50G). The differences will be in the carbeurattors, restrictor plate, exhaust manifold, etc. You will need the part numbers for all engines to see what the exact differences are. More hassle than it's worth to buy a 4hp engine then try an upgrade to 6hp, by swapping parts, as you'll invalidate the 5 year warranty.