HELP!! 90hp mercury wont plane....

Jun3Bug

Recruit
Joined
Oct 25, 2016
Messages
1
I have a 90hp mercury outboard that im about to strangle to death, lol.. im a new member here and my motor will not plane out.. here is my info...
-Serial# OC123106 stamped on motor.
-rebuilt all 3 carbs completely.
-new fuel pump.
-new fuel filter.
-new gas line w/bulb
-new rectifier (old one had bad burn spot on left connector)
-new #3 coil, old one fried due to power wire hitting it.
-new plugs
-New gas with a bit of seafoam in it.
Motor at idle is perfect, i go in gear and power her up and she goes nose up and will not plane. Trim is down to start, trim up a bit ti see if she moves and nada. Seems like there is not power to push her over the hump. Im not sure about this motor and ect as i just bought it the other day and have no idea about its history really. Compression on #1 was 115, #2 115 and #3 110 and coming up after 3 checks. Has good fire on all 3 plugs (blue arch). Motor sounds strong as a gorilla fart , just doesnt cut the mustard when a load is on it. Before i rebuilt the carbs, she ran like billy goat in a horse race. She did manage to plane out after forever riding bow up and messing with it and when she planed out she scooted. I cut her off after that and let her sit about 30min and then she ran terrible after that. After carbs and above list was performed, she cuts right on, idles like a kitten but mash the gas and pooooop... what can this be? I have a few possibilities i think... stator bad? Well she has great fire on plugs so not sure.... powerpack toast? Have no clue about that one... bad gas, non ethanol gas in tank with a smidgen of sea foam. Oil reserve is half full of merc oil, not much smoke at crank up and idle.. i have noticed bottom carb leaking a but of gas from overflow and checked it and everything seems fine. Im at a loss and i need you guys help bad... i dont have much $$$ to work with and the boat is a 1993 procraft 170 pro that i got for basically free (whish is why i have it lol)... but its a dang good looking boat and sems like it was very well took care of, was 1 owner and garage kept as i know the owner (my uncle). So any help you guys can give me will be GREATLY APPRECIATED... thank you...
 

CV16

Chief Petty Officer
Joined
Aug 30, 2007
Messages
445
Maybe try a smaller pitch prop. What rpm are you at when wot?
 

Teamster

Lieutenant Commander
Joined
Nov 8, 2010
Messages
1,923
Sounds like to much pitch on the prop,..

What pitch is on it and what are your engine rpm's??
 

SoCalBoatGuy

Petty Officer 3rd Class
Joined
May 20, 2016
Messages
75
Did your uncle have the same issues? Is this the original prop that came with the boat? Just wondering if this is a new development or if the boat has always been like this.
 

Sea Rider

Supreme Mariner
Joined
Sep 20, 2008
Messages
12,345
Is combo having planing issues lightly, medium or fully loaded ? try full throttle with trim down, once on plane trim to 90? provided that deck weight is evenly distributed. Test on flat calm no windy water cond. Combo could be bad OB/Transom height seated along badly trimmed and too much prop pitch which affects water performance.

Happy Boating
 

jimmbo

Supreme Mariner
Joined
May 24, 2004
Messages
12,944
Are the carbs opening fully? You said one of the carbs was leaking fuel from a vent(not an overflow), that means a high float setting or float needle not closing. Did you sync the carbs to the spark advance after the rebuilds?
 

60sboater

Petty Officer 1st Class
Joined
Jun 18, 2015
Messages
307
Yeah...easiest thing is punch it with trim full down...trim up if it planes.
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
36,048
I would remove exhaust cover to inspect the cylinder sleeves / pistons / piston rings.
 

DavidMoore

Petty Officer 2nd Class
Joined
Jun 2, 2015
Messages
183
Most likely, as said many times above, the prop pitch is too high for the boat. But the below suggestions are cheap and fairly easy so why not give them a try.

90 HP 3 banger with perfect idle is a rare find, I can get mine reasonable at best. :whistle:. Pound to a penny it's running on the lean side, when any error should be to the rich side. - Before doing anything else I would open up the mixture screws 1/8 turn each and see if it makes a difference. Can't hurt anything and might be all you need to do.

+ 1 also for post 6.

And fix the float on the leaking carb.

You have 3 independent engines in 1 block, to get the most out of the engine you want them all to be healthy and doing the same amount of work. So in case you don't already know it, take a look here : http://boatinfo.no/lib/mercury/manuals/70-75-80-90-100-115.html#/58

Me still thinks it the prop though.
 
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