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Help with new to me mercury 115

Z

Zbhsmith

New member
I have a 2009 sweetwater 24' pontoon with a 2009 mercury 115 4 stroke efi. We just recently purchased the boat used. When we first start off I can give it full throttle and the engine will only give me about 3000 rpm and I'm moving about 6 to 10 mph. If I pull back on the throttle to about half throttle the engine will begin to surge to a higher rpm around 4000 to 4500 and back down to 3k and I will start to gain speed. I can give it full throttle then and will only give me the 4500 rpms but if I lower it back down it will start to surge higher again until it finally gives me 6000 rpms and I am travelling at 30mph. Once it finally gives me the full throttle, I can pull it back down to neutral and back up to full with no issues for the rest of the day. But the next day it will start this all over again. I have sprayed lubricating oil on the linkage and I have cleaned the throttle body with some spray on cleaner but it was not removed from the engine. Any Ideas on what this could be. I am new to boats but I have rebuilt car engines before. It cranks on the first turn over and seems to idle just fine. Thanks
 
UKMike said:
Sounds like fuel starvation to me. Check your fuel filters, pipe and carb float shutoff levels.
Click to expand...

It's an EFI so it does not have a carb. I will however check the fuel filter again but a clogged fuel filter to me would cause it to never run right and it will after a little while but it always starts this same problem everytime I crank it up after it has sit for a day.
 
There are only really 2 conditions that can cause what you describe in my view and that's electrical or fuel, and it sounds like to me there is not enough fuel available under certain conditions. If its an EFI also check the fuel pump diaphragm. It's probably that.
 
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