Need Yamaha 90 hp performance advice

[keywestnoah]

I have a 1990 90 hp that I plan to freshen up (piston, rings, bore if needed) and was woundering if anyone has any tips to get any bonus power out of the engine with out dropping big money.

I don't mind loosing a bit of engine life...I live in Michigan, so a fresh engine can last a long time.

I have heard that you can clip a wire to disable the rev limiter...what wire?

Any performace parts kicking around for the 90?

Thanks in advance everyone!

"Anyone can drive a fast boat fast, but not everyone can make a slow boat fast."

[Lockjaw]

Hydrotec makes all sorts of stuff for that engine, a tuner, reeds, head, etc.

I would try them and see. More compression, reeds, and a tuner ought to perk it up a little.

[dash]

add finger ports and drill pistons to accomodate ports
lift exhast port to 90 deg ATDC and all intakes to 119deg ATDC
make exhast port a lot wider
shave the head as much as the water jacket will allow and remachine the tapeded squish into the head.

the rev limiter in a blue loop wire cut it to disable
if you rev it over 6500 for too long the std pistons will fail
wiseco pistons work well with extra 2 thou clearance
they rattle a bit at idle but will handle the revs

bigger carbs off a 70hp omc will help a lot but will require an adapter to make them fit

I have spent years modifying these 1140cc yamahas and the above mods will give the best performance for your money. its mainly time with the die grinder that makes the differance.

[runpasthefence]

I've been looking for something similar. I'd like to get about 105-110hp out of my 90. I've only heard that it is simple, but I don't have any hard evidence. The only products I've found are on http://www.yamaha-rebuild.com/highperformance.htm I don't know anything about them or their products, but I'm thinking about giving them a shot.

[FrenchPhil]

Key, what boat do you have ?

[runpasthefence]

I just realized that the products on the above linked page are Hydrotec products.
With these products, what kind of fuel usage differences/overall reliability/longevity differences do people usually experience?

[Fast Fred]

nice dash, looks like got it coverd. thay last

[scfireman]

Take it to Mitch Hardy in Santee, S.C. He is the man.

[runpasthefence]

Do you have any contact info? If so, I'd appreciate it if you could post it or PM it to me.

[keywestnoah]

Thanks for all the great ideas! The porting sounds great!

Help me out with the finger port idea... Humbly, I ask what are finger ports?

Any other ideas?

This is going on a 1972 16' very solid Sea Ray open bow v-bottom. This boat sounds really old, but I really like classic glass and people have no idea of the boats age (other than old 85 hp Johnson).

[dash]

Have a look at a 2.4 merc finger ports and copy them
they are two extra slots in the bore between side and centre boost ports
dont go too deep ! grind through the sleeve and then about the same depth again .No deeper other wise you will end up in the next cylinder or a hole in the block.
It can be done with a mill or very very carefully with a die grinder (practice first). Keep the tops of the finger ports rounded, You will get a little better performance if you make them square at top, but when i did it i had ring locating pins come loose real quick.
Once you have done this then put pistons in bore and line up where you need to drill the corresponding hole in the piston.
One finger port will need a hole in piston and the other will need some of the piston skirt cut away to line up.

hope this helps

[Fast Fred]

use a stone to cut the fingers, it wount jump around on ya, do NOT cut in to the wristpin boss or the piston will fail, you got to camfer the top fingers or the piston will fail.got a pic of some Yama fingers i'll see if i can put it up

[berg969]

here is a pic

[Fast Fred]

nice, whats with the head?

[berg969]

there is play in the bolt holes... i learnt my lesson put the head on before the crank goes in