Yamaha 25 hp

[bender]

jaydon...its nt worth the cash to change the reed block etc in your motor...plus you would neeed the re jet the carbys etc...i went to alexander and son in myree and got the prop on my merc 25 repitched and it got me from 20 knots to 23 on my tinny....redoing the prop on any motor maked a difference...why else would the avon boys spend hours doing it to theor 15 hp motors

[Mandurah Marine]

The 25/30 CV is a 496 cc engine and the 25 standard is 395cc

Before modifying, the most important thing to do is make sure you have the correct prop for the boats purpose. The engine needs to rev at it's upper end of Wide Open Throttle range (set out by the manufacturer) with it's fair average load (fuel, people gear) for what you are using the boat for. You need a Tacho. I use a Tiny Tach - the commercial one as it has max rpm memory so you don't have to keep looking at it. I mount the unit (with cable ties)on the tiller arm of my race motor and cable tie the one wire under the bracket which is under the tiller arm. This thing is installed in less than 5 mintues, race ready and water proof (it has been under a couple of times).
I sell these units for $130 if anyone is interested (remember it is not the standard unit and I give as much advice/assistance as needed with it to get peak performance out of your setup)

Once you know your WOT you can then fine tune the prop, engine height and engine trim - refer to my assistance above.
You might get 2 - 3 knots with just height and trim!

[leachy]

Thanks for the info. I wish mine was the 25Hp blue stripe with twin carbs at least you know its working more effeciently.

I am borrowing one of these tachos of my mate so that I can see what is going on. I had a look at the throttle butterfly last night and it seems that it not opening the whole way but I could be wrong, its a little hard to tell because the bolts that hold the air filter one also hold the carb on. I believe that the motor height is spot on, right at the to of the water, the cav plate is just below and the hydrofoil tips are just visable when running flat out. The reason that I feel it not got the correct prop and is topping out on maximum RPM is I have added front and rear casing decks, three kids and stuff and it still doing max RPM and the same speed according to the GPS. Its on a AllyCaraft 395 Discovery fairly light boat.

Regards
Leachy