2001 Mercury 90hp 4 stroke boggs down at full throttle

Big E 10

Recruit
Joined
Aug 24, 2017
Messages
3
My Mercury 90hp 4 stroke at full throttle will run fine for 3 to 4 min and then it will constantly go from 5000 rpms (full throttle) down to around 4000 rpms and then back up constantly back and fourth bogging down and back up very quickly. If you take it down to about 4500 rpms it will run forever just fine. Carbs have been cleaned, spark plugs and wires replaced. Finally I took a 6 gallon tank with me one day and unhooked the line directly from the on board gas tank and hooked up to the 6 gallon tank and it ran fine. I then took the tank out and rinsed it out, it did have quite a bit of trash in it. While doing that I checked all the fittings which seem to be fine the screen on the bottom of the pickup line is clean and it does not have a check value or anti siphon valve in it. Took it back out done the same thing at that time I took the gas cap off to make sure it was getting air no restrictions there and it kept missing or bogging down. Again took the line off at the tank and put on the 6 gallon tank and it ran fine all day. On other thing and don't know if this could make a difference the 6 gallon tank is sitting on top of the on board tank so the pickup is probably a foot higher than the on board tank. Give me your thoughts
 

ahicks

Captain
Joined
Sep 16, 2013
Messages
3,957
Fuel lines have been known to collapse internally - especially this newer stuff.
 

Big E 10

Recruit
Joined
Aug 24, 2017
Messages
3
The internal fuel line in the on board tank is very clean and ridged I don't think it is possible that it is collapsing. Thanks
 
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