Yamaha 60 hp 2 stroke,a detuned 70hp

[dnej]

I read somewhere ,the process required to up tune,if there is such a word,a 60 hp 2 stroke Yamaha, to a 70 hp.This involved larger jets,and opening the butterfly in the carbies.
Has any one done same.What is required.
Was this de tuned motor configuration the same in the 2000 model,as it is today?.
Is the prop the same size?
David

[cormorant]

Hi DNEJ

There is a lot of these style rumours about different motors and some are fact and some are fiction.

A lot was to do with marketing and having a full model range for all boats and a motor same hp as a competeing manufacturer in a perticular price range.

All I can suggestis to go on the net and get a online parts list for both the 60 and 70 and compare part numbers. If all the part numbers are the same and it is just the jets you are OK.

Generally they also had a restrictor plate or manifold insert between carby and block as well. Some did it with different airbox,exhaust, porting on block, , piston shape,head design, compression or ran dual not tripple carby and so on. Often a lot more than just jets.

Your local dealer who services your motor may be able to help but make sure it is done right as a motor can slowly die with the wrong mixture of fuel or air and you may not recognise the damage you are doing.

The USA site have lots of info but mostly on USA motors not the Jap models in regard to modifications.

You only have to look at the ETEC range to see the exact mechanicals and just the ECU computer limiting revs etc etc to get different horsepower from same mechanics.

In reality in a lot of circumstances better propping and set up on the boat or weight distribution can have as significant as affect as an extra 10 hp. Your fuel usage and useable range of power may change significantly and not always for the best.

Cor

[dnej]

Cor,
Thanks for that.It is not actually my motor.I have checked the specs,and they 70 and 60 are identical.How do I go about checking spare part numbers.Can you give me a web site addy?
Many thanks
David

[Noelm]

the may APPEAR identical but they are usually not, this is dragged up all the time, they may share a common block, but all sorts of things can be different, if you just do a carby swap, you will just end up with a dismal performing motor that uses twice as much fuel as it used to, a full check of almost every part from a factory parts manual is the ONLY way to do the upgrade, and it usually costs more than a trade in and repurchase.

[Crocodile]

I have got a 60hp and it is definately a slower revving 70.
I asked the mechanic and he says that it needs three new carbies to make it a 70, I shudder at the thought of what three new carbies would cost.
If you want a 70 buy one in the first place.

[Noelm]

it will not be a slower reving 70, they nearly all have the same WOT RPM through the model HP ranges, I have seen them with different shaped pistons, even though the had the same rings, and a parts manual revealed that the block was a different part number, mainly because the ports were different, and then there is the reeds and exhaust ,lots of stuff CAN be different.

[Achjimmy]

Nolem is right, bore and stroke are not the only factor with 2 strokes.