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Old 12 August 2012, 20:32   #11
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I though Yam 2 strokes are 50:1 (someone will be along to confirm I expect), I hope you haven't got piston pickup though lack of lube. I thought that early signs of this is for thinks to start seizing up when running hard (Hot) the piston expands and gets tight in the bore.

Short of that, the Primer bulb is prime (no pun intended) candidate, even if it appears to work normally by hand I would start by swapping this out for a new one.
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Old 12 August 2012, 20:40   #12
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Ok, I've just seen your video. Fuel starvation is the first place I would look, you could try pumping the primer by hand whilst this is happening and see if that makes a difference.

Still would check the mixing ratio of your 2 stroke.
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Old 13 August 2012, 01:19   #13
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Without having a proper look mechanical wise a quick one for starts
you say the plugs are fine ! have you Put a new set in ,, I had a similar same problem with a just about brand new engine
It would start and run fine up to about half throttle then would go on one cylinder and loose power and run rough until I eased the throttle back and it then ran on all cylinders and power resumed ,, checked plugs ,, good strong spark , but same symptoms happened again ,,
Put it the spare set and it ran fine ,

On closer inspection at home noticed that the very small ceramic insulator tip on one of the plugs was loose and was sliding up and down the electrode with vibration then shorting out the spark until the engine went on slower revs and it vibrated back Ito it's correct position and sparked correctly .
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Old 13 August 2012, 05:06   #14
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I had a similar issue on my mariner 75 2st.
turned out to be the stator coil breaking down under load.
ran fine up to 1/4 throttle. Then dropped and ran very very badly like yours is.

but go through the the usuall checks.
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Old 13 August 2012, 05:55   #15
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Morning,

Sorry I don't think I was very clear. I have a auto lube so the oil is in a separate container. What I meant is that I had a fuel tank with a oil mix of 200:1 which I used.
So more oil not less, didnt think it would make a difference with such a low ratio...

Yes I have pumped the primer and make no difference

I guess I will start with the simple and swap out the plugs and swap to another primer..

If that doesnt work I guess im going to have to take to a mechanic
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Old 13 August 2012, 16:33   #16
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Quote:
Originally Posted by jezza2011 View Post
I had a similar issue on my mariner 75 2st.
turned out to be the stator coil breaking down under load.
ran fine up to 1/4 throttle. Then dropped and ran very very badly like yours is.

but go through the the usuall checks.
My 40HP Evinrude played a nasty game on me. Ran great at idle and anything past about 1/3 throttle it would start missing and cutting out horribly. Back to idle and it ran like a champ. Sure acted like a fuel cut, but after testing everything I possibly could I made an educated decision and replaced the black box, aka the ignition control module. Problem solved!


If it is a fuel problem propane for a couple of seconds down the carb intake should tell you if it is lean or not. Don't run it off the propane very long though as it is not being lubed properly.

If the propane doesn't make a difference it is going to be electrical. Start testing the stator, checking wiring, etc. until you find the problem or can make an educated guess as to what part needs to be replaced.
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Old 19 August 2012, 07:49   #17
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I'm experiencing this as we speak.

Engine is fine until full throttle then after a while at full throttle it dies.

I've noticed that the fuel primer doesn't stay firm.

Should it and could this be the answer?
Thanks
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Old 19 August 2012, 09:13   #18
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Well I guess that could be your problem.

For mine it turned out to be low oil. My oil tank had about 1/3 left in it which is enough for about 5 more trips out for me and looked fine.

Turned out when I was cruising along the engine was level and then when I went WOT the boat rises up and would think that I had low oil. It would lower the limiter and would then decrease the lower the oil is.

Jizm made a comment about the "get you home mode" so I thought id just fill up the tank to see if it made a difference. Went out and she was fine !

Note to self, have more than 1/3 oil in the tank Big thanks to Jizm or I would still be trying to fignure out what it could be....
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Old 19 August 2012, 12:38   #19
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Quote:
Originally Posted by lockieboi View Post
Engine is fine until full throttle then after a while at full throttle it dies.
How does it die? A slow smooth death, or a fast cut? Or does it start miss firing badly then die? Is it a complete stall, or does the motor return to idle?
Quote:
Originally Posted by lockieboi View Post
I've noticed that the fuel primer doesn't stay firm.

Should it and could this be the answer?
Thanks
Have you tried pumping it and then seeing how the motor runs?
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Old 19 August 2012, 13:14   #20
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It's as if I've throttled back and then it just stops.
It doesn't miss fire or chug and splurt.

I did try squeezing the primmer bulb whilst at WOT and it still cut out.

I wonder if it's just something simple like the carbs need cleaning.
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