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,:cool:

[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?:confused:

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

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:cool: 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:eek: 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.:cool:

[Boatnut]

Thanks Fred,
Rules for super stock, pretty simple. Motor Mods unlimited:D . Gearbox Mods unlimited but must be thru box exhaust:D . 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:p

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,:eek: :cool:

[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.:eek:
Probably made myself clear as mud, hope ya get the picture and sorry bout the stuuupid question.:D

[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.:cool:

[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.:D 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.

[Fast Fred]

:cool:

[yamonster]

Do you have pics of the hull? I am building one also (90) currently it is on my 14' Alli.

[Boatnut]

Hey yamonster,
I only have a couple of progress pics at this stage. boat is covered in dust and motor bits hangin all round the shed:eek:
The boat is now pretty much back together and i've got just a few more things to do before testing. I hope to run it in the tank on Sat. If all goes well i'll drop it in the lake Sunday.
I'll get get some more pics now she's lookin' purdy and post em up next week.:cool:
is it a wingboat your building?, i ain't seen any others around sure would like to.:D
I'd be real interested in seein' what your up to. Got pics?
What motor mods have you done and how is it workin' out for ya?
what props ya runnin? A bloke racin in Sydney a couple o weeks back was runnin' a 90 yam 20" mid on a 11' boat:eek: He was spinnin a full size 24p quicksilver exhaust over chopper, said he was pullin 6500 had nose cone without low pick ups and was runnin way high, lookin for an engine rebuild i thought.

[yamonster]

Nut I am building a motor, For now I am running an Allison, When the motor is done I will hang it on a SST60 hull. For now I have the motor from my fishing boat on the alli. I did a fresh rebuild balanced the pistons, raised the exhast .080 And shaved the head to get 145 psi. raised jets one size. No LWP 26p hubbed cleaver 5800rpms GPS's @ 67.5 for now. The new motor I am building F Fred will build me a tuner and hopefully an exhast plate, Jay smith will be lightening rods and pistons, Berg will be porting a block for me. This is all happening real soon, I am working 6 - 7 days a week for now and will be wed in a month, so my project has to wait for a little while.

[yamonster]

REPORT Boatnut, We need a progress report:)

[Techteam]

Yam 90 is a good engine for tuning. I ran 76mph with a 26 yam prop and still have a cut down 28 quicksilver which was good as well.I just ordered the Bobs Machine shop nosecone for a merc v6 and filled the water intakes then used a stainless steel banjo fitting into the water pump. I recommend you tack the nosecone on with the welder but be careful not to get the case too hot just a few small tacks, if you just use the epoxy it is forever cracking. I used plastic padding chemical metal for all the fairing and it worked really nice with no cracks at all for 2 years or so.

[Boatnut]

Progress is good. Ran it a couple o weeks back but when checking bolts and stuff afterwards i got a bit spooked by what i thought was slightly excessive movement in tha big ends. I figured a freshen up would be cheaper than boring/sleeving/pistons rods crank,ya get the picture. Got it done last weekend and started running in the new rings yesterday.
Seems i'm way under propped but, 1st day out was spinnin a 14 x 22p exh over chopper ta 6800. i will be playin around with the setup this weekend but i reckon i'm gunna be huntin for sumthin with more legs.
Just coming into tha good weather here so i'll be spendin tha season workin on tha setup, this hull has only had a 2cylinder on it in it's past life so i got a lot to try for the summer.
This is the only pic I have got of it on the water so far, got a test n tune day on Sat and i will try and remember to get more better pics:) :D

[Boatnut]

yeah techteam, bobs cone with low p/u's is next on tha list but if anyone out there has anything in st/st 14"dia 24-26 or even would try 28p that they would be willing to part with PLEASE let me know:D
been keeping an eye on ebay but 24's seem to be as rare as rockin horse sh!t and the few i have seen are pretty pricey. Got ta watch the dollars, the minister of finance and war is lookin over my shoulder.
Also Yamonster congrats on tha wedding best of luck, my advice, hangon to tha toys ya got:eek: :D :cool:

[yamonster]

Boat, got the pics. Nice, keep in touch.

Team, what RPM with the 26?

I am running a 26 merc, 5900rpm. 70.5mph so far, motor is barely touched