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Old 13-05-2016, 13:02   #1
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Yamaha 2 stroke 5HP may have been tampered with

Hello: We left our dinghy with OB locked on dinghy dock at our boat club for a few nights. When we came back our OB would not fire up. Was very difficult to turn over - lots of resistance. Took it to the repair shop. They cannot figure out what is wrong with it. We are wondering if it has been tampered with and what tricks might have been done to it. Maybe we parked in someone's favourite place on the dock... a bit suspicious, but we have to think of the possibility. Is there anyone out there who can suggest what someone might do to tamper with an OB so it just does not go?? We had recently had it checked over and it was mostly fine... just a bit difficult to start recently.
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Old 13-05-2016, 13:59   #2
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Re: Yamaha 2 stroke 5HP may have been tampered with

What sort of repair shop can't get a single cylinder 2 stroke either going or saying its knackered because.....

Either find another proper outboard mechanic or take the spark plug out and see if it turns over easily. Come back and let us know how this worked.

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Old 13-05-2016, 14:22   #3
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Re: Yamaha 2 stroke 5HP may have been tampered with

pherhaps sugar on the tank?
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Old 13-05-2016, 14:53   #4
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Re: Yamaha 2 stroke 5HP may have been tampered with

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Originally Posted by Pete7 View Post
What sort of repair shop can't get a single cylinder 2 stroke either going or saying its knackered because.....

Either find another proper outboard mechanic or take the spark plug out and see if it turns over easily. Come back and let us know how this worked.

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Old 13-05-2016, 17:54   #5
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Re: Yamaha 2 stroke 5HP may have been tampered with

You need to find another mechanic. And why do you think someone vandalized your motor? Just because it won't start doesn't mean someone vandalized it.


Things happen.
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Old 14-05-2016, 09:55   #6
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Re: Yamaha 2 stroke 5HP may have been tampered with

I had someone put sugar in my engine. it didn't do anything until it got hot... the sugar crystallized and took out the bearings... no fun
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Old 14-05-2016, 10:04   #7
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Re: Yamaha 2 stroke 5HP may have been tampered with

You need a new mechanic, but first, take out the plug and see if it turns freely. If not spray it with a good dose of penetrating oil - through the spark plug hole. Now see if it turns over better. If so, your probably in luck and it should run. If not take off the head and check the bore. Hard turning over usually means it overheated and this causes the piston to swell which scores the cylinder walls. Sometimes a cylinder hone will clean it up enough to get back in running condition. Sometimes not. If the cylinder seems relatively smooth, move on down the engine to the wrist pin and needle bearings. Rare but sometimes these give out. It will be obvious if this is the problem and what needs to be replaced. Still having difficulty? With the power head removed spin the shaft that goes to the lower end of the assembly, the propeller end. This should turn freely and when you engage the fwd or reverse it should still turn freely and spin the prop. If this has drag feeling then your problem is in the lower unit. Again, disassemble and the culprit should be fairly obvious. The water pump impeller is on the lower part of the drive shaft. You might as well replace it if you've come this far. If you find that it is a shredded nub then you have the culprit. Sucking in sand, grit, seaweed or whatever over time can wreak havoc on the pump resulting in overheating. At first you might not notice unless you occasionally look to see if water is going through. If I were upset because someone took my favorite mooring spot I wouldn't bother to go get a cup of sugar and dump in, even that would need you to start and run a bit before it mucked things up. Boaters for the most part are above such shenanigans. If you really pissed me off I would just loosen the mount and slip the engine into the briny.
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Old 14-05-2016, 10:41   #8
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Re: Yamaha 2 stroke 5HP may have been tampered with

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You need a new mechanic, but first, take out the plug and see if it turns freely. If not spray it with a good dose of penetrating oil - through the spark plug hole. Now see if it turns over better. If so, your probably in luck and it should run. If not take off the head and check the bore. Hard turning over usually means it overheated and this causes the piston to swell which scores the cylinder walls. Sometimes a cylinder hone will clean it up enough to get back in running condition. Sometimes not. If the cylinder seems relatively smooth, move on down the engine to the wrist pin and needle bearings. Rare but sometimes these give out. It will be obvious if this is the problem and what needs to be replaced. Still having difficulty? With the power head removed spin the shaft that goes to the lower end of the assembly, the propeller end. This should turn freely and when you engage the fwd or reverse it should still turn freely and spin the prop. If this has drag feeling then your problem is in the lower unit. Again, disassemble and the culprit should be fairly obvious. The water pump impeller is on the lower part of the drive shaft. You might as well replace it if you've come this far. If you find that it is a shredded nub then you have the culprit. Sucking in sand, grit, seaweed or whatever over time can wreak havoc on the pump resulting in overheating. At first you might not notice unless you occasionally look to see if water is going through. If I were upset because someone took my favorite mooring spot I wouldn't bother to go get a cup of sugar and dump in, even that would need you to start and run a bit before it mucked things up. Boaters for the most part are above such shenanigans. If you really pissed me off I would just loosen the mount and slip the engine into the briny.
Second the opinion. If you get unusual resistance when you pull the starter cord you can pretty much rule out sabotage. By the way I think dumping a beer or just water into the gas tank would be much easier than adding sugar but any additives the the fuel would not cause hard cranking.
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Old 14-05-2016, 12:02   #9
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Re: Yamaha 2 stroke 5HP may have been tampered with

The last time my outboard was hard to turn over, I removed the propeller and found a bunch of fishing line wound around the tail shaft. You problem might not be the power head at all.
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Old 14-05-2016, 12:44   #10
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Re: Yamaha 2 stroke 5HP may have been tampered with

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The last time my outboard was hard to turn over, I removed the propeller and found a bunch of fishing line wound around the tail shaft. You problem might not be the power head at all.
Perhaps he's forgotten to put it in neutral (assuming the engine has a transmission).
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Old 14-05-2016, 13:43   #11
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Re: Yamaha 2 stroke 5HP may have been tampered with

p.s. is it possible that the carb. float is stuck open and it filled a cylinder with fuel?
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Old 14-05-2016, 14:18   #12
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Re: Yamaha 2 stroke 5HP may have been tampered with

Take the lower unit off, as per impeller change.
Does the engine turn now?
If not, = power head problem
If yes = Gearbox, shaft, prop problem.
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Old 14-05-2016, 14:33   #13
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Re: Yamaha 2 stroke 5HP may have been tampered with

I hope you can find a solution.

But...why is it always, first, someone elses fault? Have you performed all preventative maintenance? Have you checked the obvious? We need some more input from you about what YOU did or didn't do. If you've kept up all the normal stuff, then either stuff happens or you need a new mechanic.

Good luck, either way.
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Old 14-05-2016, 15:58   #14
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Re: Yamaha 2 stroke 5HP may have been tampered with

Sugar in the gas tank can be ruled out. Sugar does not dissolve in gasoline, try it and see. An old friends ex wife lived on his boat during their divorce thinking it would be hers, it wasn't. She plugged the toilet and cut hoses and we were afraid of sugar in the fuel till he consulted a lab about testing it and was told the sugar would stop at the filter in its granulated form if there was any.
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Old 17-05-2016, 05:31   #15
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Re: Yamaha 2 stroke 5HP may have been tampered with

Mythbusters did a segment on sugar in the gas tank - Myth Busted!
It will plug up a filter but no other problems, sugar doesn't really dissolve in gas.....
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