90hp Two stroke,Will not plane.PLEASE HELP!!

[Plyliteblue]

Hello,Im a newbie to boating,And have recently purchased my first boat a 16ft plylite Fisherman,With a mercury 90hp two stroke Outboard 1989 i think.

Well were do i start,first of all took it out for a spin the other day me and my freind and couldn't get it up on plane done everything i could to get it to plane Trim/tilt had my freind sit up on the bow,etc but couldnt do it.So i took it to the local mercury mechanics he said it was a miss firing cylinder,as water was getting on the spark and i needed to replace the water/exhaust gasket's aswell as the spark plugs.went back for Compression test and was good he aswell checked the Ignition system/coils said was good.

Yay!! and took it straight down to the lake for a spin.Was awersome could get on plane no problem's Boat was flying.Then went back to shore to pick the wife and daughter up and couldnt get on plane with them in,Too much weight? Engine started bogging down everytime i tried to open her up then all of a sudden take off but not plane...very frustrating starting to think if the motor has enough power to pull more than 2 people, maybe a different prop??I currently have a Quicksilver laser ll,20p.Fuel System???...Any idea's Would be much appreciated..

Thanks Thomas

 

[daveswaves]

Re: 90hp Two stroke,Will not plane.PLEASE HELP!!

Hello,Im a newbie to boating,And have recently purchased my first boat a 16ft plylite Fisherman,With a mercury 90hp two stroke Outboard 1989 i think.

Well were do i start,first of all took it out for a spin the other day me and my freind and couldn't get it up on plane done everything i could to get it to plane Trim/tilt had my freind sit up on the bow,etc but couldnt do it.So i took it to the local mercury mechanics he said it was a miss firing cylinder,as water was getting on the spark and i needed to replace the water/exhaust gasket's aswell as the spark plugs.went back for Compression test and was good he aswell checked the Ignition system/coils said was good.

Yay!! and took it straight down to the lake for a spin.Was awersome could get on plane no problem's Boat was flying.Then went back to shore to pick the wife and daughter up and couldnt get on plane with them in,Too much weight? Engine started bogging down everytime i tried to open her up then all of a sudden take off but not plane...very frustrating starting to think if the motor has enough power to pull more than 2 people, maybe a different prop??I currently have a Quicksilver laser ll,20p.Fuel System???...Any idea's Would be much appreciated..

Thanks Thomas

A couple of things to try. 1st, you are overpropped for that engine unless it is on a really light boat. I dont know the details of your boat and crew weight but it sounds like you are simply asking it to to too much work. 17P would be about right if you are just too heavy. 2nd, richen up the carbs 1/4 turn (all 3) if the engine leans out under load it will bogg as you describe. A lean condition will burn pistons on this engine. I assume the mechanic fixed the water intrusion problem that was initially causing one cyl to die.

 

[Plyliteblue]

Re: 90hp Two stroke,Will not plane.PLEASE HELP!!

Hi,its quite a light boat 16ft full fiberglass,New Zealand Made Dont know the weight.My wife weigh's only 60kg!!.I will try a different prop this weekend.The prop is brand new old owner had just put it on aswell as a brand new hydrofoil.yes the mechanic done the gasket change,havent noticed any water on the new sparks,just black oily type residue...Is this normal?.lHe did notice some corrsion around the bottom of the water jacket and salt deposit's.He assured me that it wouldnt be a problem...Thanks

 

[daveswaves]

Re: 90hp Two stroke,Will not plane.PLEASE HELP!!

Hi,its quite a light boat 16ft full fiberglass,New Zealand Made Dont know the weight.My wife weigh's only 60kg!!.I will try a different prop this weekend.The prop is brand new old owner had just put it on aswell as a brand new hydrofoil.yes the mechanic done the gasket change,havent noticed any water on the new sparks,just black oily type residue...Is this normal?.lHe did notice some corrsion around the bottom of the water jacket and salt deposit's.He assured me that it wouldnt be a problem...Thanks

Just my opinion here, however, the hydrofoil and the laser 11 prop have opposite reputations. The laser 11 gives you excellent bow lift and the hydrofoil gives you stern lift. This tells me that the old owner was trying to "fix" a trim condition in the boat. It sounds like he started off needing stern lift and after lifting the stern with the hydrofoil decided he needed the bow to come up more.
The engine itself might be sitting too low on the transom or perhaps the fuel tanks batteries etc need to be moved to accomodate the new conditions, ie, you and your wife. A picture of the boat would help to guide you further.

 

[Plyliteblue]

Re: 90hp Two stroke,Will not plane.PLEASE HELP!!

Here's just a few pics.

 

[daveswaves]

Re: 90hp Two stroke,Will not plane.PLEASE HELP!!

Here's just a few pics.

Nice looking boat, I went on the Kiwi boatyard sight to look at the Plylites before you sent the pics, it thought that might be the design. OK, first off I would not call it a light boat per se. Granted it is lighter than a lot of boats out there but I suspect that your total weight comes in at around 1850 pounds. Of more importance for your set up the boat appears very front heavy which may be why the previous owner tried a higher bow lift prop. The problem is you need a prop with more surface area and less rake. The laser 11 does not really shine until speeds over 50 mph. I run the exact same prop on my aluminum bass boat that you see in my avitar. It is 18 feet long and only weighs in at 1100 pounds and just draws 4 inches of water. I am powering it with an older merc 1150 which is equivalent to your newer 90 in hp at the prop shaft. Even with my set up I am underpowered for that laser 11 20P. This winter I will be changing the power head to 150 hp which will give me about 120hp at the prop, which should then come into its own.
My suggestion would be to remove the whale tail it will not help. If you can try a 17P I think you will be in the ball park. If you have any weight that you can move aft to move your center of gravity further back I would try that as well, fuel tanks, batteries etc. Think of a teeter totter with .you on one end and a child on the other. You move closer to the middle to make it work. Same with your boat. Don,t be afraid to use your trim and tilt as you take off. Tuck the engine in at the start and trim it out as your speed increases, you will feel the bow lift and you will feel the difference in your steering wheel.

 

[Plyliteblue]

Re: 90hp Two stroke,Will not plane.PLEASE HELP!!

Hey,just a Update,

So far i have replaced the prop with a 17p,Removed carbs and rebuilt aswell as new fuel lines,Shifted things around to get even Weight distribution,.Taken off Hydrofoil.But i am still having the same problem will planeand get to WOT with just me in the cockpit and wont with anymore people.Argg!! frustrating..The only thing i can point to is the gasket replacment.Am i still getting a water intrusion??..spark plugs look fine.

 

[daveswaves]

Re: 90hp Two stroke,Will not plane.PLEASE HELP!!

Sent you a pm.

 

[bryanwess2000]

Re: 90hp Two stroke,Will not plane.PLEASE HELP!!

I see some of this has been addressed but you should be ok with a 20p prop
with 90hp on a 16' boat unless it's a tank. I run a 21p on a 16' with an old
85hp merc with a 2.3 ratio LU like yours. I experienced a similar problem and
narrowed it down to the fuel system. After cleaning and adjusting the carbs
and rebuilding the fuel pump the problem remained. I went through a couple cheap primer bulbs before buying a mercury/quicksilver and that solved the problem. I think it's a fuel line fitting leaking air or your primer bulb. When your alone you get on plane and the rpms raise quickly and doesn't cause afuel starvation problem. When you have additional passengers it puts more
load and fuel demand on the engine and rpms don't rise fast and supply
enough fuel and can reveal a problem in your fuel system. I had this problem with additional passengers. Get someone to prime the bulb while your trying to
get on plane and see if that makes a difference.
P.S. I've had to replace the clamps on new fuel lines that were letting air
leak into the fuel system.

 

[daveswaves]

Re: 90hp Two stroke,Will not plane.PLEASE HELP!!

I see some of this has been addressed but you should be ok with a 20p prop
with 90hp on a 16' boat unless it's a tank. I run a 21p on a 16' with an old
85hp merc with a 2.3 ratio LU like yours. I experienced a similar problem and
narrowed it down to the fuel system. After cleaning and adjusting the carbs
and rebuilding the fuel pump the problem remained. I went through a couple cheap primer bulbs before buying a mercury/quicksilver and that solved the problem. I think it's a fuel line fitting leaking air or your primer bulb. When your alone you get on plane and the rpms raise quickly and doesn't cause afuel starvation problem. When you have additional passengers it puts more
load and fuel demand on the engine and rpms don't rise fast and supply
enough fuel and can reveal a problem in your fuel system. I had this problem with additional passengers. Get someone to prime the bulb while your trying to
get on plane and see if that makes a difference.
P.S. I've had to replace the clamps on new fuel lines that were letting air
leak into the fuel system.

Good thought, however, his lower end is a 2:1 ratio not 2.3 to 1. If yours is 2.3 to 1 that would explain why the 85 hp is able to swing the 20 p.

 

[jasonbailey]

Re: 90hp Two stroke,Will not plane.PLEASE HELP!!

My old outboard did the same thing with just one of the fuel tanks that I carried. I discovered a bad O ring in the quick disconnect that was causing it to bog down. New O ring, and it ran great.

 

[bryanwess2000]

Re: 90hp Two stroke,Will not plane.PLEASE HELP!!

My mistake on the LU ratio. I researched some newer 90hp mercs and they
had 2.3 gears so I thought they all had that ratio. Thanks for clearing that up.

 

[bryanwess2000]

Re: 90hp Two stroke,Will not plane.PLEASE HELP!!

If all else fails try an eletric fuel pump that can supply at least .6lbs/hp
fuel an hr. as a temp fix and to diagnose if you have a fuel supply problem.
But you shouldn't run it this way long term, it's probably illegal. I'm sure there
are better ways and someone may point them out, but this is the way I
confirmed my problem.
Edit: Sorry I forgot your in new zealand try a pump for a 120hp or greater
or whatever KW rating that would be. Forgot about needing to convert to metric system.

 

[sschefer]

Re: 90hp Two stroke,Will not plane.PLEASE HELP!!

Sounds to me like your engine was leaned out and overheated at some time and your exhaust plate is warped. The gaskets you just had replaced are failing again and your original problem is returning.

Take it back to your mechanic and have him look into the cylinders for shinny or lightly taned piston tops. Compression and leakdown tests will not discover this problem and plugs will often look fine.

This is a tough problem to troubleshoot but your mechanic nailed it the first time so it sounds like he's on it.

 

[daveswaves]

Re: 90hp Two stroke,Will not plane.PLEASE HELP!!

Sounds to me like your engine was leaned out and overheated at some time and your exhaust plate is warped. The gaskets you just had replaced are failing again and your original problem is returning.

Take it back to your mechanic and have him look into the cylinders for shinny or lightly taned piston tops. Compression and leakdown tests will not discover this problem and plugs will often look fine.

This is a tough problem to troubleshoot but your mechanic nailed it the first time so it sounds like he's on it.

Actually no it doesn,t, different gasket problem that he was having. This is more of a boat/prop/set up issue, not an engine issue. Originally he did have an engine issue,however that is fixed and he currently runs aro 5200 wot, so he is not starving for fuel.

 

[Plyliteblue]

Re: 90hp Two stroke,Will not plane.PLEASE HELP!!

Yes i dont think it is a fuel problem/gasket.I'm leaning toward's the fact that there is a problem with the motor/boat arrangment.Maybe water in the hull??..BUT! at this point i will consider anything..I rang my Mechanic Today he was surprised the prop change didnt have much of a effect on the perfomance other than i was getting a loss in top end speed when compared to the 20p i had on...Said it might need a overhaul but I think he said that cause he's running out of idea's...

 

[Texasmark]

Re: 90hp Two stroke,Will not plane.PLEASE HELP!!

Hi,

I had an '89 115 and it was the 40 year old design with 6 cyls in line, with the metallic clamshell shroud around the engine, as was the 90 of that year. The 90 had the 2.3:1 gearbox whereas the 115 had the 2.0. Big difference in performance with a big load for a given prop. I currently have a 2002 90 and it still has the 2.3 gearbox. the engine in your pic appears to be a 3 cyl with a plastic clamshell which makes it a 2000 or later.....for the record.

If your boat stills runs out to your satisfaction lightly loaded, you have your answer in front of you. You need more power from your engine. Either the engine is not delivering, the prop is not letting it "spool up" to it's available hp, or you have a trim/height problem.

Weighing the boat would be a plus if you could tow it over to some scales. Allow 500 or so lbs for the trailer and 300 for the engine. The rest is the boat. Knowing that number will help. The other thing with that boat is that the wind resistance is a consideration which can retard your performance......but that retard would be there pretty much regardless of the occupancy.

My current 3 cyl 90 is on a 17' aluminum boat, pad hull, low wind resistance, weighing in at around 1600 lbs on the water with me and all, running a 24P SS wheel and I have no problem hitting 50 mph on a cool day. I can add 300# of weight and only drop 3-4 mph. Right now, I personally don't have a problem with your current prop on that boat with 2-3 passengers.

You need clean fresh gas, clean fuel filter, clean plugs, and all your pulse paks working for you. Those 3 cyls will drop pulse paks, you can take that to the bank and you may not notice it with a light load, but load the boat up and you will surely notice the loss of a cylinder. BTDT

The way I test them is to put the engine on muffs at home. Set the N rpm to about 1500 and one at a time pull off the plug wires at the plugs. If you pull all 3 wires and get equal results in engine degradation with each wire
(pulling and replacing one at a time) then all the paks should be ok. However, if you have one or more that don't quite produce the degradation in performance that another one produces, then suspect that pak. You can get them on the www for less than $100 each.

After all that you could look into trim angle and any peculiarities with the hull.

Run the tests and get back.

Mark

 

[Texasmark]

Re: 90hp Two stroke,Will not plane.PLEASE HELP!!

More:

Black oily residue is normal on the plugs.

I see a mountain in the background of one of your pics. What is the altitude where you run the boat? If it is more than 1000 feet, give or take, you will have a reduction in power caused by thin air which means that you will have to prop down (lower pitch for larger load than you have/I mentioned) and may need your high speed jets replaced with ones to suit the altitude.

These engines have fixed high speed jets. The only carb "tweak" that you have is the idle/low speed adjustment which has no impact upon your ability to plane.

Mark

 

[sschefer]

Re: 90hp Two stroke,Will not plane.PLEASE HELP!!

Next time you talk to your mechanic, ask him if he put a ehxaust cover/plate kit in it or if he just changed the gaskets. If he just changed the gaskets then have him put the repair kit in it this time and your power problem should clear right up. This is a well known problem which is why Merc makes the repair kit.
Edited: Tell him to look at the Induction Manifold/Reeblock page of the parts manual. The kit is usually #1 on the page. The part number will vary depending upon the actual year of your engine but if Tex is right and it's around a 2000 then the part number should be 42878A2 and it's around 140.00 retail.

One last thing. I think the labor charge is about 1 hour.

 

[Plyliteblue]

Re: 90hp Two stroke,Will not plane.PLEASE HELP!!

Hey People.

I'v been messing round with the motor today,and found some Interesting thing's that might be contributing to my problem .Well i started the engine then one bye one took the lead's off each plug listning for any change in sound and performance,the bottom cyclinder i had problems with the intrusion of water on that spark was good decrease in performance as you would exspect so as the middle cyclinder but the top cylinder had no change in noise when i pulled off the lead.Im guessing a dead cylinder,Also i was getting a shock from the leed everytime i touched it,even pulling it off with vice grips that has a rubber handle.It seems like there is spark going into the lead but im thinking most of the spark is coming out the leed somewere,why im getting a electic shock.I'm going to swap leads around tonite and see if i will get a change.I just working up the courage to do it as it hurt like hell!!!...Should i buy a new power pak? and wires??..My mechanic Told me to look into the reed valve mite be a problem there.

Thanks,Thomas