Set-up Advice Please

[Oz Dude]

Hi All,

I just found your little corner of the net and am hoping you guys can help me both now and in the future

My boat won't be familiar to you as I live in Australia. It is an Australian Bullet (different to what you have over there) and it is 17.5ft long.

It is a light-weight ski / skirace boat and runs about 400lb as a bare hull (3 guys can pick up a bare one and move it aorund).

I've owned the boat for 10 years and have run a Merc 3L 225hp on it the whole time. Due to an engine failure I took the opportunity to upgrade from my carby engine to a newer injected model. We are also now going to use it as a ski-race boat (was just a fast social ski-boat) and as such, we undertook a few mods to better set up for ski-racing.

The problem is it's now a dog out of the hole and I'm trying to figure out which change made the most change if you know what I mean.

Old Setup:
3L Carb Merc 225hp
1.87:1 Gearbox
2" Manual Jackplate
21 gallon rear mounted gas tank

New Setup:
3L Injected Merc (with 250hp computers)
1.75:1 Gearbox
4" Hydraulic Jackplate
28 gallon rear mounted gas tank
11 gallon front mounted gas tank

The rest of the boat is unchanged save for some minor glass work, a new coat of paint underneath, and some new gauges.

Now I know that changing the gearbox ratio will change how the boat runs but wow, this thing went from a monster holeshot to a kitten. Previously I could run a 28" Trophy Plus and not feel a skier come out of the water verses now that the same prop won't pull the boat up onto the plane by itself!!

All 3 props I had previously (21 Quicksilver, 26" Mazco, 28" Trophy Plus) seem to be utterly useless and I'm steadily loosing what's left of my tiny mind.

The only thing we could get to work was a 21" Laser but I've got 250hp pushing stuff all weight and I should be able to prop up a hell of a lot further than that. We tried a 23" Laser but while it pulled out ok on a calm day, turning it into the wind in some chop resulted in it pulling initially but then vented, and kept on venting until we gave up. The skiers basically just got up and then started sinking back down.

The Mazco will pull out but only after excessive ventilation and that's boat only. It won't pull out skiers. Last weekend we borrowed a hand-built 26" Tubed Cleaver and it seemed to pull as strong as the 21 Laser so that gave me some hope.

This weekend I'm hopefully getting my hands on another cleaver but this will be a solid hub so I don't know how the venting will go

The problem is I just can't seem to get the other props to vent at all so we can't build revs. Other than gearbox and moving the motor back 2", there's no huge differences and I've gone form something that was sweet to total frustration.

So you know what it looks like I've attached some pics.

I know you guys don't do a lot of river ski-racing over there but you do have a lot of experience with running fast so I'm hoping you can help me find my way back to smiling again.









Cheers & Beers to All,
Oz

[JP Love]

Wow.... Cute boat...

[gary slagle]

wow,that is one awsume skiboat! have you tried lowering motor a bit?

[benski]

Another 100lbs of gas doesn't help your holeshot too much either.

[Oz Dude]

JP Love - Thanks I like it Not too shabby for a 1992 worn out race boat that I restored 10 years ago!

gary slagle - The jack plate is set as per our ski-race rule book which is maximum height of 1" below planing surface and I have just under 3.15 inches of travel down from there

benski - agreed about the added weight (plus extra weight of hydraulic jack plate over old mechanical one) but like I said, the difference seems way bigger than that

It's like the motor just can't seem to rev and therefore bogs down. The prop I really can't understand is the Trophy Plus. It's got the large plugs in it AND it should be getting a little bit of over hub exhaust at take off but...nothing. Full throttle results in 1,500rpm and ploughing through the water (boat only).

So far, the only thing I've picked with the Laser is that the holes are chamfered to push the exhaust directly at the blades as opposed to the Trphy Plus where the holes just point outward.

Can anyone else shine some much needed light?

Oz

[JP Love]

Dont warry """Lots a good guys here to help""" When they have time=========== Remember.. Good night body,, J-P

[JP Love]

Why dont try a Chopper big ear....??

[Oz Dude]

Is there much of a difference between my Mazco 26P and a Big Ear Chopper?

I really know so little about props because the ones I had always worked so well so I've never really looked into it...

Oz

[JP Love]

V-Bottom wow I think you can do the job Chopper.. Trophy is not bad but a 3 blades for your asset... See the answers... No body leave you alone on this thread,,, J-P Love

[Oz Dude]

Thanks mate - I'm guessing others will chime in over hte next couple of hours.

Oz

[JP Love]

No Problemo.... J-P

[JP Love]

wow,that is one awsume skiboat! have you tried lowering motor a bit?

Yeah the shaft


Look high on trailer..

[Alan Power]

Taller gears, moving the motor back plus extra fuel/weight in the rear probably isn't helping a lot.

When you say you upgraded the motor did you rebuild the damaged motor with an EFI set-up or is it a different motor? How healthy is the motor, compression?
Check timing and pickup.

You say the replacement motor has 250 computer, is it a lower HP motor with a 250 fuel curve, may be running rich.

Try some simple things first like empty the aft fuel tank and fill the forward one to shift some weight!
Is the prop blowing out on takeoff or loading up?

Alan

[JP Love]

Not bad weight help sometime to balance... Is a issue... Yes

[Oz Dude]

Taller gears, moving the motor back plus extra fuel/weight in the rear probably isn't helping a lot.

When you say you upgraded the motor did you rebuild the damaged motor with an EFI set-up or is it a different motor? How healthy is the motor, compression?
Check timing and pickup.

You say the replacement motor has 250 computer, is it a lower HP motor with a 250 fuel curve, may be running rich.

Try some simple things first like empty the aft fuel tank and fill the forward one to shift some weight!
Is the prop blowing out on takeoff or loading up?

Alan

Hi Alan - thanks for chiming in...

The old motor blew No5 piston and was traded against the current motor. It's a 1999 model 225 3L EFI with computers off a 250. It also has 4 butterflies on the intake (2 top and 2 bottom) as opposed to the standard 225 that only had 2 at the bottom. As far as I am aware, the computers are only giving the motor a bit more timing advance so the 25+HP should all be top end anyway.

When we first put the motor on it seemed very sluggish so the guy at the shop took a look at it. He buys and sells quite a few 3L motors and this one was bought under the premise that the powerhead was a Precision Rebuild from Mercury as the original had suffered an oil injection failure and grenaded.

After he took it for a water test he agreed something was wrong. He pulled it down to find that the powerhead was original and had signs of substantial wear. As he sold the motor to me he then guaranteed it and rebuilt the powerhead himself. It didn't need new pistons but the block was honed, new rings, etc fitted. Basically a fully rebuilt "new" powerhead.

When we though there was still an issue with the motor, we swapped it out with a spare one of my skiers had just bought (also second hand) which resulted in exactly the same results with the props I already had.

This further confirmed that we have a set-up issue more so than an engine problem. The motors were swapped back again on Monday night so we will now try the borrowed props we have on my motor to see what the results are but I'm still really confused why my Trophy Plus 28P just will not pull out of the hole. Both it and my 21 Quicksilver just load up and don't go anywhere.

Conversely as I said in my opening post, my 26P Mazco has excessive ventilation out of the hole that only just gets it up on plane boat only. You don't stand a chance with skiers.

Do you think the motor should be loading up like that? I know it's now a taller gearbox and it's been shifted 2" further back but it really seems like night and day compared to the old carby motor.
Oz