[fishfulthinking]

i just put on a 1990 mariner 90hp 3 cyl on my 17' sportcraft center console. i went out to a river in md today and with 3 of us it wouldn't plane. granted we are all big guys but we weighed maby 600-650 lbs and my capacity plate says 880 lbs. i would throttle up and it would run up to 3000-3200 rpms but just wouldn't climb on plane. two of them in the very front of the boat and i was in front of my console steering over the windshield so all the weight we could was forward. my boat weighs about 1100 lbs. my prop is a stainless steel quicksilver with 19" pitch. once i ditched the passengers it planed right out and ran great.
i just see lots of boats my size with 75-90 hp outboards and they can't all run this way.
the bottom of my hull is clean with no buildup at all and no barnacles. i am at my wits end and don't know what to do now. i want to be able to take out my friends but it is a bit embarrasing when a 15' aluminum boat with a 20 hp motor goes by us.

any suggestions?

[bhile]

Is the motor mounted correctly? The anti cavitation plate should close to even with the bottom of the boat to 1" above.

[kenmyfam]

As posted check the set up and if set up height is good, consider dropping the pitch a couple of inches or so.
How did your previous motor go on it ?? what was it and what was that set up ???

[Texasmark]

The Mariner 90 could be 3 or 6 cyl. Bein it's a 90 I think that was the first year for the 3 cyl. Makes a difference as the gearboxes may be different....trying to remember if the 6 had a 2.0 or 2.3 like the later 3 cyl version.

The point of my statement is that if you have a 2.3 gearbox, a 19P should work just fine.....all things considered. If you have a 2:1 then it could be a bit large and as Kenny point out you would need to drop a couple of inches in pitch.

The fact that you unload the boat and it performs just fine is ok, but some numbers would help, like what does just fine mean...rpm's, speed, and while you're answering, how many cylinders.

Mark

[Texasmark]

Reread post and saw 3 cyl. Sorry for the confusion but would still like rpm and speed data. Also, what type hull do you have, in particular at the transom, round, hard chine, slight V, deep V, flat bottom, and what do you have in the stern of the boat....like batteries, fuel, live well, and heavy type things.

I run a 24P on a 17' alum bass boat (3 step pad hull) with that engine and lightly loaded it runs 50 mph at 5600 rpm. Lightly loaded is 250# of me, 3 large batteries, 10 gallons of fuel and tackle....boat weighs about 800# dry.

If I fill up the live well (25 gallon estimate and it is right in front of the batteries and fuel which are at the transom) or add a passenger, hole shot performance drops drastically, top end doesn't care all that much once I get up and get going. Dropping to a 21P makes a big difference in hole shot but is inadequate at WOT....rpm's go up to 6000.

Curious that even with all the weight forward it wouldn't come on out of the hole.

Where do you set the trim when you are hole shooting? Tucked all the way in? It can make a huge difference where it is.

Mark

[CharlieB]

First thing to try is have a passenger pump the primer bulb as you throttle it.

A marginal fuel pump may supply enough fuel for a very lightly loaded craft but fail with much more load.