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Loosing power at full throttle

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gundog1

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i have a 2003 50hp mercury two stroke. motor runs great after leaving boat ramp, once i slow down to do some scouting for ducks i try get back on plane and motor has very little power. does not stall out. i have had carbs rebuilt, new tank, filter and all hoses from tank to carbs. motor does not sound like it is missing and no vibration. I am able to idle and drive but very slowly. Primer bulb stays full. if i switch off motor and wait a minute motor starts up and able to get full throttle and up on plane but within 30-45 second slowly loose power. very frustrated and confused. open to any and all advice and thank you on advance
 
I had a very similar problem with my 40 HP Merc. I finally figured it was a fuel starvation problem. The fuel line quick disconnect was the problem. I got rid of it and hard plumbed it and put in a bronze fuel shut off valve on it. I have never had a problem since that day.
 
Yes I had removed the gas tank cap and no change. Also had replaced all the quick connections with hard plumbing. Thank you for your advice
 
Nope! I am not totally familiar with your 50 so pardon me if I error. Fuel pump? or the possible short in a electrical part such as a coil., Sounds like a simple thing but they usually are not. Been thru this kind of thing with my old 50 but that was to be expected. Not ready to enroll in a 12 step program just yet.
 
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I am also wondering if the fuel pump might be the issue. Might just replace her to eliminate it. I'm changing out the plugs this afternoon as that is my last thing I know I can do. Next step mechanic as much as I hate to do it might just have to.
 
There have been times when I would have been better off to take it to a trusted mechanic and leave it there. I do get help from a retired Mercury mechanic but I hate to lean on him for everything. Throwing inexpensive parts at the problem is a logical thing to do for an illogical problem.
 
I only have one more though, If there is any moisture in your fuel it will cause a problem like that with a paper element fuel filter. You don't want to know how I found that out.
 
Makes sense to take it to a professional
would I be able to see the moisture in the fuel filter?
thanks again to everyone for helping out.
 
gundog1 said:
Not recently to my knowledge. I've owned it for two years and haven't done it.
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Some of the experts here, ask if you could squeeze the bulb when it slows to get a better handle on whether or not the fuel pump is faulty. Never had it make a difference, personally. I never suffered a fuel pump issue, either.
 
Here is a thought. If the carb float is hanging up on the gasket or the float level is not set correctly. It could limit flow of fuel into the carb bowl. With the carbs off the engine, if you give them a gentle shake, you should be able the hear the floats rattle around inside the bowl. You have covered most of the fuel restriction possibilities.

You didn't specify if the problem occurred before or after the carb rebuild.

Another possibility is exhaust restriction, either carbon build up at the exhaust ports or a out of place gasket in the motor leg.
 
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