yamaha 50 wont go over 2000 rpm

[vroom ZOOM]

Hello

I have a yamaha 50elf (89) that wont go over 2000 rpm once warmed up. I went boating the other day and it was fine. let it warm up and it would go slow or fast, anything you wanted it to, except that it would get a little stuck when revving up under load in the 2700 rpm area. the next day, i let it warm up as usual, but when it reached 2000 rpm, i kept pushing it to go faster but it only died. I tried tuning the carburetors (did i spell it right?) and it was good again. as soon as it cooled down I tried going again, and if I got to high rpm could I could sit there and it worked there for the rest of the day, as long as I did not drop below 4000 rpm. if i let it drop below that when warm, I could not get back over 2000rpm unless I waited for it to cool down and then accelerated while it was still cold. this one stumped me, since I am usually good with fixing these engines. i will try seafoam and changing the plugs.

 

[99yam40]

carbs should not need to be readjusted ever, unless someone jacks with the screws
if they get dirty they need to be taken apart and cleaned, set to spec in manual .
keep running a lean running motor and you will toast piston/cylinders

 

[211libwtfo]

I'd check your anti siphon valve.

 

[vroom ZOOM]

excuse me, where is it. I don't think I have one, it's only if the fuel tank is higher than the engine when this valve is required. it keeps the gas from siphoning into the engine when it is off. Anyway, after an inspection of the engine I found the bolt that holds the fuel pump onto the crankcase was loose. I tightened that and it seemed to do the trick. And then it began again, but the bolt was still tight. the engine idles at around a crazy high 2000 rpm with no load, and just in gear trolling speed is 1500rpm, and it sometimes dies. now even when it is cool it will not go over. I tried pulling the choke and revving over the "bad" rpm range in gear, and it worked. once above 4000 rpm it's totally fine and planing. I use no ethanol 91 octane gas in it, and the previous owner had used this type of fuel in the engine too. at first, with the loose fuel pump bolt the spark plugs where wet. after tightening the fuel pump bolt the wetness burned off and they turned dry with a brownish colour. I put new plugs in.