Yamaha 2001 F100 loosing power when warm

I have a problem with my engine that has left me and my local Yamaha dealer out of ideas.
The engine starts and runs smooth. when running at 5000RPM for 15 minutes or so the engine starts to lose power, the RPM will drop to 4500 down to 3000RPM within minutes. it runs fine once the revs have dropped to 2500RPM.
If you prime the fuel bulb it picks back up to max revs for a couple of minutes, then loses power again.
I have renewed the fuel filter and all fuel lines from the tank to the two pumps to no effect. I have also renewed the diagphrams in both pumps and last week connected a remote tank directly to the fuel filter on the outboard but this hasn't cured the fault.
My dealer has also stripped, cleaned and balanced the carbs but this had no effect.
Any help would be much appreciated as I am now struggling to think what else it could be, and my boat is parked up in the good weather.
Many thanks in advance,
Gaz

[boats.net]

Run it on a 6 gallon portable tank to determine if problem is on motor or in boat fuel system.

Friend of my have the problem like yours on the top his alarm starts going (problems white the fuel) ………His mechanic install for him new fuel feeler on the side of the boat to his tank and the air house from the tank was to long and they make small bend it was trapping the gas inside engine did not have air that it was not running .I hope that is maybe what cure the problem. Good Lock
Misiu

Hi,
Thanks for the help so far.
I have tried fitting a 6 gallon portable tank, I connected the pipe from the remote tank directly to yet another new filter in the outboard motor.
The short length of pipe that goes from the output side of the fuel filter is brand new and I have renewed both fuel pump diagphrams.
My Yamaha dealer has measure the output of each fuel pump and said the pumps are good.
The engine was still loosing power then picking back up for a couple of minutes if the primer bulb on the portable tank was primed again.
Any advise would be appreciated as both me and my dealer are now stuck for what else to do.
Many Thanks
Gaz

[boats.net]

When they cleaned carbs did they clean or replace fuel filter in fuel inlet in carbs? Number 44 at http://www.boats.net/parts/search/Ya...201/parts.html

Thanks for the advice, I didn't know them filters were there, I removed the carbs today and checked the filters, one was particularly bad but all were dirty.
I have taken all 4 filters to the dealer who supposedly cleaned the carbs & he claimed he didn't know they were there. He is going to renew them and we will test the boat on Friday.
Thanks for the advice, with everything else I have done I was out of ideas.
I will let you know how the engine performs with the new filters.

All 4 of the small in-line filters were changed and the boat is running perfectly after covering about 30 miles in it this weekend.
Thanks for the help, & I hope this thread can help someone else out with the same problem

Cleared up the SAME problem for me too.

Thanks for the post. After taking things into my own hands i fixed my engine like the dealer mechanics couldn't. I took the whole intake and carborator assembly off of the engine so i could avoid linking and syncing the carborators again.I'm posting some picutures for further assistance.