yamaha 85hp flatspot.

I have just put my 17ft fletcher in the water for the first time this year after checking it all over mechanicaly-new impeller,plugs,clean fuel filter,check fuel pump diapham,check and clean carbs+new fuel.
The problem that I seem to have is when I put the throttle to full, the boat accelerates up to 3000-3500 rpm then seems to bog down a bit then carries on to wot at 5200 rpm with me in the boat only. It did not hit any flat spot last year and acclerated smoothly to all the way to wot 5200rpm.

Also while testing it, at a couple of times it seemed to get stuck around the 4000-4500 rpm limit for a very short while like it needed more fuel.

The outbord revs cleanly , idles well, trolls well,no problem on the plain at 3000-3500 rpm,

I brought the boat home,checked fuel pump,and filter, tank primer bulb and cant seem to find anything wrong.

Please anyone have a possible idea.could it be something serious internally?

Re: yamaha 85hp flatspot.

Fatten-up the idle mixture screws another 1/8 turn and re-try. You might have to go another 1/8 beyond that, but I'll bet no more. Sounds like you're pretty close already.

Re: yamaha 85hp flatspot.

Thanks for your reply,sorry for my ignorance-the mixture screws are 1.5 turns out,when you say fatten them up do you mean turn them out or in,and if you turn them out does that richen or weaken the mixture-outboard is premix model.

Re: yamaha 85hp flatspot.

All of the symtoms of a fuel restriction. My first quess as to where would be the fuel pump. Mainly because if the carbs were done right, its the only thing you haven't done. Second guess would be the fuel line disconnect.You can just plumb around it to test.

Re: yamaha 85hp flatspot.

I will try the items mentioned and as soon as I can get it back on the water I will test it again,then get back to you.
If any one has any more ideas of items to check I will do so.
Thanks for all your help

Re: yamaha 85hp flatspot.

I took the carbs of again and double checked them just to make sure I didnt miss anything,Seemed spotless,then I took the engine fuel line dissconect off and cleaned it as suggested.

Took it back out to test and apart from a not so good idle-bit lumpy(I guess this would be the mixture settings?)-it would accelerate cleanly up to WOT without the flatspot.My guess It was the fuel line dissconect.

Thanks to all for the advice-fantastic forum with very helpfull people.