90hp,1140cc(69.5ci)yamy pro's and cons

[Boatnut]

I am in the process of puttin together a 14.5ft (4.5m) drop deck wingboat to run in the 1250cc class here in oz. the closest mota i can find that is readily available is the 2str yamy 90 with 20" mid. All the other makes seem to be way under or just over. alum jacking plate with 4" setback and prop will be a st/st 24p exhaust over chopper to start with. I would appreciate any comments on the potential of this mota. I will start with a bog stock unit and progress from there. i would like to know where i could expect to end up and would appreciate a bit of wisdom from anyone who has tickled up these things in the past.
Thanks
Regards Chris

[Fast Fred]

it will respond well to finger ports. needs bigger carbs,

[Boatnut]

Got the Motor swinging from the roof of the shed, gearbox off. Needs new bushes in the swivel bracket and got some stubborn bolts in the mid. i will make steering arms, and jack plate is on the way. I am looking for suggestions for a nose cone with low p/u's. does Bob's machine shop make one and do they have a supplier in Australia? (gunna start out in 1250cc super stock which stipulates thru box exhaust)

Also Fred, you mentioned bigger carbs, which one's? will put a set of boyseen's in for cheap insurance while i've got the carbs off but a part number would be handy. as for finger ports could you please explain further or point me to a thread that already covers it.

the motor has a big bucket of oil gettin in the way so i thought i would chuck it and remove the pump. a plate and gasket over the hole is easy but i would appreciate some info on what to do with the wiring. cut it or earth it?

does this motor have a rev limiter? and if so which wires need cuttin?

Got power tilt and trim but only going to need trim. has anybody removed the tilt ram only? can it be done? (it's 5kg or so that i figure i don't need to be cartin around.)thanks

Regards Boatnut

[Fast Fred]

well best have a look at the Moda rules i think you can dump the tilt ram
lookin at the book, them is the bigest 1bbl carbs they make, have them machined, rules , read the rules, they most likely don't tell ya what you can do, just what you can't do on the Boyson reeds, they make two different sets, i'm not sure what the number is for 90hp yamaha reeds, but what ever it is
tell them you want the "R" ones, so like 000 are the reg fiber reeds you want the 000R ones them is the two stage reeds, No stops.

[Boatnut]

Thanks Fred,
Rules for super stock, pretty simple. Motor Mods unlimited . Gearbox Mods unlimited but must be thru box exhaust . No 'racing' mid or quickfoot. Commercialy available fuel (pump gas) or avgas, no addatives. No blowers or hairdryers, No Nitrous . Only one motor per boat

We are moving into winter and having the worst drought in over 100 years here (Nearly all Victorian rivers and lakes are empty) so this will be my winter project. I will probably be driving you blokes nuts with stupid questions for the next few months. I have been running the Bridge to Bridge powerboat race on the Hawkesbury river in New South Wales for a few years in a 25hp boat. Times are about the 1hr 15min mark. It's time for a bit more pace and the plan for this boat is to smash the one hour barrier.

Thanks again Fred, I appreciate your input. I also enjoy reading the threads on this site and am getting a real lot of practical info from them.
Regards
Boatnut

[Fast Fred]

whos got the tig welder, put some big reeds and blocks on it, on the exhaust
you can take the first plate and cut the center out, and move the back wall
of the exhaust out,( use the cutout one as a spacer), bigger carbs, electric pump, dry exhaust,

[Boatnut]

So are you sayin' cut the curved part of the first plate and remove? the cover plate then needs the notches welded to keep water from exhaust passage. This would increase chamber volume a fair bit and square off the back wall, would exh gas flow allright?OR get another inner plate, cut guts out and use as spacer under oringinal inner plate. The curve that obviously asists the flow of gas would still be in there, just further out. This would still allow cooling water around exhaust but not increase chamber volume by much.
Probably made myself clear as mud, hope ya get the picture and sorry bout the stuuupid question.

[Fast Fred]

cut guts out and use as spacer under oringinal inner plate. The curve that obviously asists the flow of gas would still be in there, just further out. This would still allow cooling water around exhaust but not increase chamber volume by much.

thats the one i've tryed, worked, but for the most part, it just moves the the wave up higher in the rpm range, that may or may not be what you want,
cow bell style tuna works well on that moda, 86 the exhaust box.

[Boatnut]

Grouse, Thanks for clearin that up, exhaust box gone, water diverted out the back of adaptor, gotta get it all back together and see what it does on the boat before i change too much more. What ya said would work well cause it's easy enough to try and if it don't suit, can always take it back out.
Thanks again for the reply, Keep ya posted, I'll post pics and numbers when i get sum.

[iwanajohnson]

go to http://www.yamaha-rebuild.com/, that's hydro tec marine's website. they specialize in yamaha high performance. they're in nixa, missouri but they do really good work and can make a yamaha run. i'm thinkin bout gettin the same motor and I'll have their stuff on mine if I get it.