Help! Boat won't get on plane!

[QuestionablePlay]

Hey guys, just bought my first bass boat and I'm having a problem with it getting on plane. It's a 1994 Nitro 170 DC Rick Clunn Edition with 115 hp Evinrude, I got a hell of a deal on it so I felt like it was time to pull the trigger. We've had it on the water twice now, both times having the same issue. We had the throttle full bore and it just kept plowing through the water. Eventually it did plane out, but not until it mulled through the water for a minute or two. I noticed that it would get up out of the water quicker if we'd put her in a turn, or if we started to catch a little chop in the water. It would also plane if one of us sat on the bow. We've had the ear muffs on it out of the water, and that engine will flat out run, great response, and sounds good. On the water the engine hangs up at 2500 rpm until it gets on plane, where it gets up to 4000 rpm, before settling back in around 3000. Carbs have been rebuilt and all new plugs. Compression test was also done, I'm not sure about a trickle down test. I have a raker 13.5 x 20 prop on it. I'm just wondering if you guys have any suggestions? I've read or been suggested a different prop, lowering the motor on the transom (mine is on the top holes), timing issue in the motor, or I have a prop cavitation. A guy on another forum said he had a similar problem with the same engine and said the pistons were eating rings. My father and I are both at a loss, he's owned multiple boats in his day, but they were all inboard ski boats, never an outboard with a 2 stroke. Thanks in advance!

[cfalco]

Well if you are sure the bottom is not full of crap, algie, dirt whatever and you are sure you engine is tilted all the way down when you are trying to go then drop your prop pitch 2 degrees and try it.  You can look up the engine on this site for the suggested pitch and rpm https://turningpointpropellers.com/  then compare it to the pitch you have on there now.  Even if the pistons are wearing dropping the pitch a couple of degrees will get any boat on a plane faster.   You lose a little top end by doing that but you get right out of the hole.

 

I bought a boat once on a good deal and had the same problem.  I talked to the guy I bought it from and he stepped right up and told me he had taken off his stainless steel prop right before he put it up for sale and he had an "old one" laying around.  Stainless can cost up to three times more so he did not want it to go at the price I gave him.  

 

Propellers are a big deal, you have to have the right one to get out of the water and you dont want your pitch too high because you can get up to a high speed and blow up the motor so stick as close to the suggested pitch and size that the manufacture recommends .    

 

As to buying a prop from the above link be careful, they are great props but most times you have to buy a new hub and also a new trim tab.  They sit back an extra inch and most motors have to have the other upgrade parts for them to work so you wind up spending twice as much.  But at least that site will get you in the ball park on size and pitch.  If it says you need a 17 pitch and you go outside and you have a 22 that is your problem.  If you engine is getting weaker, compression wise you wont kill it by going down a couple of points.  

 

Good luck, have fun, catch big fish and throw them back.  

 

Oh and once you know what you need go to amazon they are the cheapest

My bet is he took off the stainless you most likely have a too small and wrong pitch on there

[fishnkamp]

The first thing I would do is remove the prop and have the hub checked . it may be spun.

Next trim the engine down and measure from the engine cavitation plate to the bottom of the hull.  We call it pad to prop height.

A good prop shop should be able to help you get in the ball park.

[WRB]

Does this engine have power trim?

The centerline of the prop shaft should be 3 1/2" below the plane pad with the engine cavitation plate paraelell with the plane pad in the center of your boat.

Sounds like you have the engine trimmed incorrectly, it should be all the way down to get your boat on a plane, then trimmed up to increase speed by lifting th bow about 3/4 trim up on the trim indicator. At full speed you have about 5,800 rpm's at Approx 45-50 mph.

Tom

[QuestionablePlay]

The engine does have power trim, and the prop falls within the parameters of what's suitable for this engine, according to what I've read online. We'll have to check the hub and do some measuring. Do you guys think a power pack failing to fire could be the issue? Thanks or the suggestions, please keep em coming! 

[Way2slow]

Could be too much prop, but haven't looked at what should work. Do a little research and see what other setups like yours run and if they are running similar pitch then start checking the engine.  Not knowlng what kind condition the prop is in, might want to try and find someone with a similar pitch prop that you could try.  I've seen numbers of props with rolled blades that looked just fine just looking at them.  Also, I don't see this being a possible spun hub.  Spun hub usually pulls good to a certain point and the motor acts like it goes out of gear, the rpm's skyrocket but the boat does nothing.  With yours not making good rpm, that's more in line with a bad, or too much prop, or a bad motor.

 

My thoughts are the motor probably has a problem.  What you are describing is a classic symptom of a motor down on one cylinder.  Understand, 4/6 cylinder two strokes, can have a mix fire on one cylinder and make you think they are running fine.  My first test would be a leak down/compression test. 

Next I would do a plug dump.  Get it on plane and run WOT for about five minutes.  Switch it off while holding full throttle, don't let it idle.  Pull the plugs and they should be paper bag brown.  If one is black, that's a bad cylinder that's not firing or the gas mixture is way off.  If all are black, the motor is running way too rich.

Also, don't forget to look down the throat of the carbs and make sure the plates are going fully open.

[WRB]

Don't believe from what you have posted the 20P prop is the issue or the hub clutch is spinning. If you know how to operate the power trim properly then that isn't your problem.

We are all second guessing from our experiences what your problem might be.

Way2Slow is far more knowledgeable then I am. I agree you may have under power issue with your OB and a compression check with tune up is where to start. Check your fuel supply, filter, gas line, prime bulb everything to with fuel including draining and adding fresh gasoline and oil. I am not familiar with your engine, however power packs are difinately a possibility as you are experiencing low power symptoms.

Another problem with a plane problem is the boats weight distribution could be bow heavy, so take everything out. Glass bass boats your age can develop a hook in the boats plane surface if stored on a trailer incorrectly. Get a straight edge and check the plane surface pad for any dips, it should be absolutely flat for about 6'.

Good luck.

Tom

[Fishing Rhino]

My 2009 Nitro Z-7 had this same exact problem.  The motor would rev up, but the boat would take what seemed like an eternity for it to labor its way up onto plane.  My problem was not enough pitch.  The motor revved, but did not have enough thrust.

 

I bought it new at the BPS in Foxborough, MA.  They thought I had changed the prop.  I had not changed it.  They swapped it for a prop with two inches more pitch, from 21" to 23" if memory serves.  Problem solved.

 

How you have the weight distributed is also a factor.  Too much weight in the stern will cause the stern to squat and be sluggish getting up on plane.

 

In the meantime, here's a handling trick you can try to provide additional lift at the stern.  Steer the boat slightly left and right when you take off.  It pushes the stern sideways a bit providing additional lift.  It may take a bit of experimenting on your part to get the technique down.  How much steering input and how quickly you steer back and forth are what you'll need to learn.

[blackmax135]

On 7/11/2017 at 6:34 PM, Bass2Mouth said:

The engine does have power trim, and the prop falls within the parameters of what's suitable for this engine, according to what I've read online. We'll have to check the hub and do some measuring. Do you guys think a power pack failing to fire could be the issue? Thanks or the suggestions, please keep em coming! 

It could surely be a power pack. Take one plug out at a time and make sure they are firing (do not hold the plugs with your hands when the motor is running).  Do not run it again until you get it fixed.  I had the same problem on my 1994 mercury and ended up being that water was getting into one of the piston's.  i kept running it and it fried the piston.  Not saying thats whats wrong with yours but it is a possibility.   With it only getting up to 2500 rpm at full bore while trying to get on plane your motor is loosing power in one of your pistons.