WOT speed on a '83 20' SF w/200

[spareparts]

they closed lake X!
Bllue Heron, back to the subject at hand. First, i have not had a lot of luck with the mirage on an outboard, too much blade surface. Now the Mirage plus works much better than the original Mirage on an outboard, but if the boat were mine, i'd probably try a Laser, its designed to give more bow lift, and you can run it higher on your plate, if a laser is not available, try a simular prop with some rake to it. And before you go any farther, put a straight edge on the hull bottom, make sure you don't have a lot of hook in it, if the boat was ever on a roller trailer, or on a trailer that wasn't set up right, it could have hooked the hull, don't be suprised if you see a little hook, its probably normal, but any dips or excessive hook could explain the whole problem. And by the way, what are you using to check your speed?

[Bigshrimpin]

Spareparts - They closed placida too back in the early 90's. My point is that Mercury has contributed more than any other outboard company to the engineering and developement of the carb two stroke outboard.

[spareparts]

i guess i should have said it like this: they closed lake X
i aleays wanted to go there, i knew a coupel of guys they went there during some testing, said it was like going into a secret government operation

[NoBones]

Lake X is alive and well.
In Brevard County, Florida
Just off I-95
From what I understand it is still used for testing on
occasions by Sea Ray which has a big plant on SR-528
by Port Canaveral.
See ya, Ken

[spareparts]

last time i was in Mercuiser School, they told me the owner of the land, didn't want to renew with Brunswick, wanted to leave the place natural, so he kicked Brunswick out, I think the lake you're talking about is a differnt lake( they had facilities on over 6 lakes in Fl alone). The preoperty Lake X was on is said to be one of the best places for hunting in FL, only problem is, no hunting is alowed

[Blue_Heron]

First, i have not had a lot of luck with the mirage on an outboard, too much blade surface. Now the Mirage plus works much better than the original Mirage on an outboard, but if the boat were mine, i'd probably try a Laser, its designed to give more bow lift, and you can run it higher on your plate, if a laser is not available, try a simular prop with some rake to it.

I've tried two different mirage 21p props, same part number, but an inch difference in diameter (one 14 1/4", the other 15 1/4"). Neither is optimum for this boat/motor combination. I've got a prop that I think is a laser 22p, that I was running on my flats skiff, and it performs a little better. I don't have a jack plate on the Seacraft, but this prop didn't mind surfacing on the other boat. I'm gonna raise the engine another inch and give her a try.

And before you go any farther, put a straight edge on the hull bottom, make sure you don't have a lot of hook in it, if the boat was ever on a roller trailer, or on a trailer that wasn't set up right, it could have hooked the hull, don't be suprised if you see a little hook, its probably normal, but any dips or excessive hook could explain the whole problem.

Hull's pretty straight. Only about 1/8" of hook in 4'.

And by the way, what are you using to check your speed?

GPS

BTW, you sound like you know a little about these black motors. I've disconnected the timing module. What's the maximum advance I can safely run if I keep the WOT rpms under 5600?

[spareparts]

i don't like advancing them any more than factory spec, in fact i usually back the timing down 2 degrees just to make sure they live. the fuel has changed a bunch in the last several years, this alters the fuel mix, if I was running a light boat(bass boat or go fast), i would play with the timing some( you pay attention to weight on a fast rig), i would probably add some octane booster, and or run higher octane fuel,but for a fishing boat( where the average weight and load change from one extreme to another), i would tend to err on the side of caution( i also step the jets up one size). On that rig, if you want more speed( assuming you get the current setup figured out) step up to more HP, try a bonafied 200/225 XRI( not to criticise your frankenmerc, i've had a couple run pretty good for what i had in them), or step up to a 3.0 225/250. I still think you have something left in the rig you have. If you have the oil injection pulled off, go ahead and spin that thing a little more( keep it under 6000), we used to twist the crap out of those motors, I'd rather have one that turns, then one that lugs. the mirage props you tried, were they Mirage or Mirage plus? We used to have some luck out of Turbo props also, go up one # in pitch over the pitch you have now, stay away from the turbo four blades( never had any luck). I can't remeber if you posted whether you weighed it or not

[spareparts]

just thought of a couple of cheaper and easier things to try, get someone to take a picture or video of your boat running at speed, take a look at how wet you're hull is( how much is in the water), check the angle of the t-top( is it acting like a parachute?). Sometimes a picture will save a lot of steps or open your eyes to something that you never thought of. Second thing, have you thought about putting a manual jackplate on it, shop around, you can probably pick up a used one for $100, they make it easy to set the engine height, its not as sweet as the hydraulic ones, but it still helps, it should bring the bow up a little as well, depending on the setback. You could really fine tune the setup, a jackplate is cheaper than another prop.

BTW, what kind of skiff do you run?

[Blue_Heron]

Hey, Spareparts. Thanks for the suggestions. I wanna touch on all your points, so this is gonna be a long post.

First, I'm not sure which factory timing spec to use on this motor. XR6? 200 carb? 200 EFI? (that's what the powerhead is). They range from about 18 deg to 26 depending on model year and the timing module they came with. I'm just looking for the maximum I can safely advance the timing with the module disconnected. One mechanic told me 21 degrees, another said 23

I rejetted the WMV-3 carbs with the same mains and backdraft vent jets called for in WMV-18s. I left the idle jets alone. It runs fine, in fact, there was no noticeable change in performance. I'm thinking the bigger mains give me a little safety margin on timing advance. Am I on the right track?

I'm not really trying to make a race boat outa this thing, just wanna get the full potential outa the engine I've got. Though it might be cool to get 50mph outa the thing, I don't go that fast very often. My skiff will hit mid fifties, but I usually cruise at 30-35.

Oil injection was not installed when this motor was thrown together. I'm thinking of adding it back. I have a complete system off a friend's merc V6. His ate the gear on the crank.

The Mirage props I've tried are numbers 48-13702-A40-21P and 48-13702-A41-21P. Not sure if either is a Mirage Plus. I've looked for a Laser II on Ebay and haven't found one that fits the large gearcase in the right pitch. Between the Seacraft and the flats skiff, I have quite a prop collection from my ebay shopping.

You're right about the hull running wet. I can't seem to get the bow out of the water even with a lot of trim angle. I was hoping someone on the board has a Seacraft Industries 20SF hull and we could compare notes. I suspect my hull is more bow-heavy than the Potter 20s. I don't have a t-top, so that's not slowing her down.

My flats skiff is an '87 Action Craft Flatsmaster with a '91 XR4. It's got a polling platform, hydraulic steering, hydraulic jackplate, fiberglass push pole, and trolling motor. It's old, but it goes just fine. It cost me about a quarter of what it would for a new rig set up with the same options.

[ThePHNX]

Blue Heron;
Ours is an SF20 but till we've repropped we're out of the water, anyway, at this point it would be the blind leading the blind - in fact you sound like you know a hell of a lot more than we.
Don't know how much land based performance tweaking translates to the water, but when we were trying to get the last inch of speed and power out of a custom engine - or even relatively stock - we'd standardize fuel and stick with it, set the cams with a degree wheel, choose plug heat range CAREFULLY, and advance spark till she pinged and then back it off a hair. Such empirical methods have the advantage of dealing with the engine's `personality' there are no two exactly alike. HBH