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help needed boat not able to plane

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Dave Simpkins

New member
so i have a problem where the motor gets to 2800rpm under load, but won't go past 15knots. without load goes to 5500rpm. things i have done so far, replaced fuel filter, and in line fuel filter, rebuilt carbys and fuel pump, all cylinders have compression and spark, slightly off timed but not the issue. changed gear oil and still won't get up on the plane. response is good at low speed from takeoff but not high end. motor seems to want to push harder and labours at 2800 like something else is stopping it. it is a 1999 60hp mariner 3 cylinder. any help appreciated as i have spent a lot of dollars and am pulling out what is left of my hair.


dave
 
See if you can borrow a prop with far less pitch from someone and give it a try. If that cures the problem, you need a less pitched prop. If not, then look into motor problems (bad ignition on one cylinder, a bad carb, etc.) Do the prop experiment first, however.

Jeff
 
sorry i should have given a bit more info, i bought the boat with the motor on it, older boat with a repower back in 2000. when i bought it it had around 150 hours on it and i assume the boat yard did the maths on size for weight and prop size and pitch etc. it ranwell, used to get up on the plane easily and cruise 40 to 45 knots on the plane. i hadn't used it for 12 months as the pee tube or tell tail became blocked down to a trickle at high revs, then i just put it as one of those jobs to do. fast forward12 months, fitted a new thermostat and gasket, no avail. new fuel filter fuel lines and fuel, no avail. fuel pump rebuilt no avail, carby rebuild still no. removed prop and re greased and also removed lower unit and changed oil and impeller,and it still won't go on the plane. motor seems responsive enough and like it wants to push harder but something is holding it back.

dave
 
You stated it will do 5500rpm without load, hopefully you are not just throttling it it up on land!!! How is it peeing now since repairs? What is your compression? These motors are bad about cylinder sleeves slipping if lugged or overheated..
 
i have been doing the no load both on land and in water, and yes with flush muffs put on too so not to screw the impeller. as for compression, 120 seems to be the magic number, i am not sure what they are meant to be from factory but i get the same reading across all three cylinders, so from my limited knowledge i dare say the sleeves and cylinders and rings etc are all still good. when i bought the compression tester i also bought a timing light so i will do that too, then take it out again to see what happens.

could it possibly be from when i removed the lower unit and re installed it? i know i have to put it in forwards to re insert it properly, but is it only just or in wot position?

dave
 
nah don't have a manual, checked the timing though, and basically on 0, if not about 2 fly turds off it. i think the carbs need to be synced with the timing as they have been off and it is just starting to miss fire. as for spark, i tested them to the bottom of the cowling and got nearly an inch away on the middle cylinder and still sparked, i am starting to think the lower unit is the problem more than anything. and now i have had it off again i cannot put it into gear
 
yeah it seemed to be ok at all connections as i had tested the pump into a bucket both before and after rebuild, and better flow after it was done
 
just a random question...is that a fiber glass boat?......could it be leaking and you are waterlogged between the floor and the hull?unless i overlooked it you never did say what kind of boat your are running.....length...width....weight etc....does the motor have power trim?....is the boat on a plane angle when you are trying to get rpms up?...is the bow digging in?what exactly do you mean by no-load and loaded?one person unloaded?what are you calling loaded?are you calling loaded just in the water?are you running that engine at wot with the muffs out of the water?if so you are going to wipe that motor out if you havent already done so....
 
it is a glass hull and when i take the bungs out there is maybe half a gallon of water, i have inspected the hull for holes and cracks etc, but having a non removable false floor i cannot see where it is coming in (suspect the bung) it is a 15 foot half cab older hull mid 80's weighs about 650 pounds, beam of about 6 foot 5, it has power trim and tilt, i have ran it in the water trimming it up and down to try to assist it getting on the plane, with 2 people on the main seats the stern sits lower in the water, however with someone sitting on the bow whilst in motion it levels the boat out but still won't plane. what i am calling loaded and unloaded, is in and out of water, with load being water resistance on the prop. i have run it on land once in wot for a couple of seconds to see if it reaches planing revs without load as a benchmark, simply to see if it will do it in gear, which it does.

why do you say i will wipe the motor out in no time? i would have thought if it has muffs on and is pumping plenty of water through it still has cooling power equivalent to in water doesn't it, from my understanding no other parts need cooling from the bottom of the motor down. the gear case may be the only thing but for only a couple of seconds i don't see the harm, as for the prop, it is exhaust through the prop, so in motion there is little water if any in the centre of it.
 
did you look at the bottom of the boat in the area where it hits the trailer when loading boat onto the trailer....that gets banged up pretty good on some rigs when driving a boat onto the trailer.....the amount of water that drains is not the point..if its waterlogged then the water is into the flotation and everything else.....park the boat on a good incline and pull the plug and drain it...check later and see if it is still getting drips an hour later.....let the boat dry out as best you can and have it ready to run and launch it and run it right away....see if the performance is better before it has time to accumulate water.....drying it out will be the problem....especially if it has wood stringers etc....water may even be trapped between stringers depending on how the boat is built...
 
drying it out will be the problem....especially if it has wood stringers etc....water may even be trapped between stringers depending on how the boat is built...
Click to expand...
You can not dry out wet floatation foam. Floor has to be removed and replaced, wet foam removed, hull, stringers and transom dried and sealed w/CPES (best product) and new closed cell foam installed.

CPES=Clear Penetrating Epoxy Sealant. If the wood is wet you are better off gutting the hull of all wood and installing new sealed wood and glassing it in place. You'll do a better job than the original boat builder. Allow drain openings between stringers. Been there and done that. It is about a 40 hr job. Remember, epoxy sticks to poly but poly does not stick to epoxy. Shoot me an email if interested in more tips on DIY.
 
Have the motor checked on a dynomometer.------------If it is producing proper power then the problem is with the boat.------------------Winding a 2 stroke motor up in nuetral in the driveway is bad for the motor.------Nothing to do with cooling though.
 
thanks guys, when the boat was stored, i had all storm covers done up and bungs out, so i would have thought any water that got in would have got out too, i have checked where it sits on the rollers and all the fibreglass seems to be pretty good. and i have never driven the boat on either for a reason, not to damage the hull. and short of getting a camera on a stick i think the inner is fairly good too. i have spoken to a local marine shop telling them what is wrong and what i have done thus far, being both fuel filters, carbys timing compression fuel pump checked spark etc on the motor. he said it may be the stator, not getting enough power at wot cause the windings have burnt out or something, anyone else have an opinion on it? or could it just be the power packs for each plug. if i don't get the problem sorted myself i will have to cough up the cash.

also i only ran it in wot on land to get a benchmark to see if it will do it without load, not a regular occurence by any means, once i established it is possible then every test since has been on water under load
 
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