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Old 03 May 2015, 16:07   #1
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First Time out with the Zodiac, Major Problems with the Engine...

I just took my boat (and engine) out for the first time today. There seems to be a major malfunction with the drive system, at least that is my best guess. The engine didn't have much difficulty starting up at first launch, however it soon quit on me out of nowhere on the middle of Pistakee Lake. It kept quitting on me throughout the day, forcing me to restart it time and time again. But back to the story, after some finaggling I was able to get it restarted, and putted along back into port. The gentleman who ran the boat rental shop was kind enough to come take a quick look, his opinion was that the engine itself was running okay, so I decided to try topping off the buoyancy tubes and keep with air, thinking that may be the issue. I had called a Zodiac dealer to get his thoughts, that was his best suggestion.

It did not really solve the problem. My first suspicion there may be a problem was the high speed sound of the prop whirring/chopping through a mixture of air and water at full throttle, as if there was a major cavitation or ventilation problem. Though, ventilation is unlikely, seeing as how the boat is designed for a short shaft motor and the keel/tubes were verified to correct pressure by my Bravo pump. The starter motor was also acting up on me quite a bit throughout the day.

As I continued my test of the boat, I found that full throttle would produce enough thrust to raise the bow, but not actually get up onto plane and speed. The best I can describe is that I was getting 1/4th the amount of thrust I should've been at full throttle 80% of the time, and a rev to 7000rpm and very quick planing out 20% of the time. In essence, I was either going 6mph or 20mph at full throttle depending on what the motor was doing at that time. The tach is set to 4P, as per Mercury specs, I had a Mercury on the phone with me as I set up the tach. The prop chopping/whirring noise could be from it overspeeding in the water, turning too fast. The strange thing though is that the RPM at full throttle setting was seemingly correct when (getting way too little thrust from the motor), at around 5200rpm. Only when I finally started getting some power did it jump way up to 7000RPM.

Just as an aside: Fuel was automobile gas, with 50:1 oil mix of Quicksilver Premium Plus, along with one ounce each of Mercury Quickcare, Quickleen, and Quickstor. Fuel line is equipped with Attwood fuel demand valve (this is a factory pre-assembled Mercury fuel line). Also, I am not sure if there is a thermometer-metered water cooler, but the pee stream varied from a halfway decent stream to just kind of a dribble. If there is a thermometer, I would like it yanked out, not seeing a decent stream is disconcerting. I can turn the prop by hand in the same direction the prop would be turning in forward gear, while it is in forward gear. It makes significant audible (and felt) clicks when turned. I cannot turn the prop by hand either direction when gear selector is in reverse. Not sure if that's relevant information, but the Zodiac dealer I was able to get a hold of had me do that as an on-water inspection and said it was his assertion i shouldn't be able to turn it at all by hand in gear.

I took a video, which I uploaded to YouTube, to show the problems I was having. The link is below.



Please let me know what you think about what is going on with this motor... It's still under warranty from the shop I bought it from, they will apparently cover any costs for repair of defects 90 days on from first use.

https://scontent-ord.xx.fbcdn.net/hp...36&oe=55DBC5F5

https://scontent-ord.xx.fbcdn.net/hp...9c&oe=55D9D52F
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Old 03 May 2015, 16:47   #2
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Could be allsorts of things. Prop slipping on hub, gear linkage not adjusted correctly so the gearbox isn't properly in gear ( not good if you've been hitting 7000rpm ) This might also account for the repeated stalling if the engine has a shift assist/start in neutral protection. Don't mess about posting on here, get it back to where you bought it from asap before your 90 days is up.
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Old 03 May 2015, 16:53   #3
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Originally Posted by Pikey Dave View Post
Could be allsorts of things. Prop slipping on hub, gear linkage not adjusted correctly so the gearbox isn't properly in gear ( not good if you've been hitting 7000rpm ) This might also account for the repeated stalling if the engine has a shift assist/start in neutral protection. Don't mess about posting on here, get it back to where you bought it from asap before your 90 days is up.
I had someone tell me that from the YouTube video, they thought my tach was off. Though it's set properly, I checked what setting it was supposed to be at from multiple sources including Mercury.

I've already emailed the shop my explanation and the video. The process to get everything fixed is in motion. The thing that still scares me is the noise I heard coming from the prop, I hope it's just from the fact it was overrevving and not an inherent problem I have with my boat/engine setup. I had my Bravo manometer inflator aboard to make sure all the tubes and keel were topped off at 3.5psi.
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Old 03 May 2015, 16:56   #4
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Does the speed of the boat increase when the engine over revs?


Love the name of the lake BTW
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Old 03 May 2015, 17:18   #5
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Hi all

I would be trying a different tach .No way is that reving to 7000 RPM.Possible fuel starvation issue Or electrics.
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Old 03 May 2015, 17:25   #6
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Spun hub sounds plausible and a problem with the shift mech.... Possibly it has hit something before causing what you describe?

Probably also needs carb looked at.

It doesn't sound like it is hitting 7k in the video to me but I wouldn't use it again until your shop verifies it.

Cheers
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Old 03 May 2015, 17:43   #7
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Originally Posted by Pikey Dave View Post
Does the speed of the boat increase when the engine over revs?

Love the name of the lake BTW
There is a MASSIVE difference in thrust, and thus speed, when the RPM decides to go up when my throttle is at full. The bow rises, but doesn't go to plane, when the indicated RPM is at the usual 5100. When it spikes to 7000+ (as indicated), i get an almost scary amount of power.

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Originally Posted by Xk59D View Post
Spun hub sounds plausible and a problem with the shift mech.... Possibly it has hit something before causing what you describe?

Probably also needs carb looked at.

It doesn't sound like it is hitting 7k in the video to me but I wouldn't use it again until your shop verifies it.

Cheers
People keep telling me the tach is off, but I'm not sure how that could be the case. I have it set to what Mercury instructed, which is 4P, and it's a Mercury brand tach. Though I agree it doesnt *sound* like it was overrevving, but I'll just take the entire lot (tach, fuel tank, and all) to a different shop.

The engine has never hit anything that I am aware of, I had these problems from the get-go of using it. I am the only owner of the engine since being purchased after rebuilding.
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Old 03 May 2015, 18:01   #8
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You did open the vent on the fuel tank didn't you?
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Old 03 May 2015, 18:05   #9
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You did open the vent on the fuel tank didn't you?
There is no vent on my tank. As of a few years ago, all fuel tanks sold in the US must be anti-venting as per EPA regulations. There's an automatic vaccum valve on the cap though to let air in if there's a negative pressure gradient, it just wont vent air out. I also have an Attwood fuel demand valve in the line to prevent an overpressure of fuel to the motor.
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Old 03 May 2015, 18:09   #10
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Ok. Had a similar issue before and was because I forgot to open the vent lol. Have you checked the cap is working correctly as if it is not replacing the used fuel space with air it will create a vacuum and cause pretty much what you are experiencing.

Could you run it with the cap loose to see if it works
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Old 03 May 2015, 18:09   #11
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I have the same 15hp engine and have previously owned the identical Mariner. These have been used on various SIBs from 3m to 3.6m... air, alloy and wood floor models at different times.

Some random thoughts...

I too don't think the RPM maxing out at 7000 rpm is true... sounds a little lower to me... more like 5500rpm when you are showing 7000. Also when you have hit an idle that looks higher on the tach than I'd expect.

Inflatables are imperfect beasts even when fully inflated (air floors more so obviously but yours looks like a hard floor) so they can suffer weird "slipping" feelings at max power. I've experienced this many times and it depends on loading, how the boat is trimmed, the wave state... even prop type and condition.

To me yours doesn't sound like a mechanical slipping of the gearbox as it's not that bad.

What's your boat loading balance like? To me with you, fuel tank, fixed transom wheels & battery etc in the stern it looked like it might be a bit bow high?

What weight are you and your passenger?

Are the transom wheels dragging in the water at all on the plane?

I think you are saying if it drops off the plane sometimes it doesn't easily get on the plane again. That can happen even with a 15hp if you guys are heavy, with a full fuel load plus battery etc... particularly if you are loaded too much towards the stern.

Do get used to the telltale variation with this model due to the thermostat. It was designed to run with a stat so leave it in.

The cutting out looks like a fuel starvation or inlet air leak issue. I'd be wondering if there could be any blockages in the fuel line or fuel filter. Also if the fuel pump diaphragm was OK and then of course is the carb dirty inside blocking the jets at idle.

Also these engines will stall like that if the idle mixture is too weak. See this thread...

http://www.rib.net/forum/f36/2-strok...out-65026.html

Also note this thread where I had a slow running/stalling issue with my Mercury 15. It was a hard to see hose that had split on the carb...

http://www.rib.net/forum/f36/mariner...arb-67447.html
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Old 03 May 2015, 18:16   #12
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I mentioned this sort of "slipping" at max power/speed can be the prop type or condition.

For example I had this slipping feeling with my Mariner 15 when I fitted it with a new correct pitch Solas aftermarket prop. Swapped it for a genuine Mariner one and the problem was cured.
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Old 03 May 2015, 18:36   #13
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Kestrel I've just looked at a few of your previous posts to see if I could see what model your inflatable was and see it's a Zodiac 350 alloy floor weighing 150lbs. Just as a matter of interest I had a Honwave 3.5 that weighed about that and that was much more sluggish getting onto the plane (when loaded with two "not slim" adults plus a teen) than an air floor model of a similar length that weighed 50-60lb less.

But more importantly I noticed you say this of your motor...

....funny story about that engine I bought the other day. Turns out it had been on a water mouse originally, and then the fellow who owned it had it run dry (I'm assuming he meant dry of oil with clean gas) by his kids. Whole thing seized up, and the shop he sold it to spent about a grand completely rebuilding it since the outside looked spotless.


I do hope the running issue is a simple fuel thing but I have to say the above information would ring alarm bells with me when the motor was proving unreliable from your first use of it. Not that uncommon for folks to do what they call a full repair after a major overheat yet the outboard never runs totally properly again.
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Old 03 May 2015, 18:37   #14
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Originally Posted by Fenlander View Post
I mentioned this sort of "slipping" at max power/speed can be the prop type or condition.

For example I had this slipping feeling with my Mariner 15 when I fitted it with a new correct pitch Solas aftermarket prop. Swapped it for a genuine Mariner one and the problem was cured.
A quick question if you don't mind, what pitch prop do you think I should be running?
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Old 03 May 2015, 18:48   #15
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Standard will be fine as it's all I've used and has been perfect... think that would be a 9.5"... I'll check it out.

Or perhaps 9" is standard??
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Old 03 May 2015, 18:53   #16
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I can't completely rule out anything, but I personally doubt it's fuel tank or line related. It's a new tank, and new line. All standard stuff, nothing hodge podged together, it's all the proper Mercury connectors.

The guy who came over to look at my motor revved it up while keeping the gear shaft from engaging and putting it into drive, without the drive train engaged the thing revved up like a champ. My strong inclination is that it's drivetrain related.
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Old 03 May 2015, 19:02   #17
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Just looked... both my current Mercury 15 and the previous Mariner 15 used the standard prop which was 9" pitch.

Re the no load revving out of gear... it doesn't work how you are thinking. The water puts a load on the prop and therefore the engine so an outboard that is trying to push a boat that won't get on the plane properly will bog down well below it's maximum revs. Even misbehaving engines will rev to max in a no-load situation... it's the behaviour under load at lower revs in a real life on the water situation that's crucial to an outboard performing well.
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Old 03 May 2015, 19:04   #18
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First Time out with the Zodiac, Major Problems with the Engine...

I once had some issues with a brand new engine ,
1st one of the spark plugs had a broken ceramic insulator tip that looked ok gave a good spark it wasn't until a very close inspection after a change to the spare set of plugs that we noticed the insulter tip broken, it would start fine & run up to about 1/2 throttle then the power would fall , as soon as the throttle was backed off it ran fine again & would start with no problems .

Later we also looked at the float bowl on the carb that was full of particles of white sealant that had come from the overzealous person at the factory assembling the fuel pipe fittings on the tank that had passed through the primary filter .
Just a thought ?
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Old 03 May 2015, 19:09   #19
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Kestrel on your video around 2.30-2.40 were you altering the throttle to cause that drop and rise again in the revs?
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Old 03 May 2015, 19:48   #20
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Quote:
Originally Posted by Fenlander View Post
Just looked... both my current Mercury 15 and the previous Mariner 15 used the standard prop which was 9" pitch.

Re the no load revving out of gear... it doesn't work how you are thinking. The water puts a load on the prop and therefore the engine so an outboard that is trying to push a boat that won't get on the plane properly will bog down well below it's maximum revs. Even misbehaving engines will rev to max in a no-load situation... it's the behaviour under load at lower revs in a real life on the water situation that's crucial to an outboard performing well.
True. I didn't think of it that way. Truth be told I'm not sure at all what is causing the problem, I don't think my tank or line is defective but I'll bring the whole kit anyway.

To answer your question about the video, at 2:33 I brought it back down and advanced it back to full at 2:40. You can see the engine rev up on its own back to full thrust at 2:47. Throttle position didn't change during 2:40 to 3:00. You can see it change RPM spontaneously at the very start of the video, too. Anything above 5000 indicated is at WOT, though the actual RPM varies.

Is the starter motor supposed to whir and spin like a top as shown in the video? Sometimes after a failed restart it'd give me that (very disconcerting) noise of spinning long after having been disengaged.
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