Thread: 200hp Merc Not Opening Up

Check your fuel line for restrictions. The gray "ethanol resistant" lines have a liner that will degrade and break up. The fragments will collect downstream at the fuel connector. The anti-siphon valve can be problematic on older rigs as well.
Also, engine setup will make or break how the engine runs. If the motor is set too low on the boat, it may not have the ump to turn that prop. Despite the fact it could on a bigger boat while set correctly.
Several mechanical issues could cause your symptoms. A bad switch box, a broken reed, incorrect timing, low float levels, detached tuner and a restrictive fuel supply are a few that come to mind.
Two things that I would suggest,
1) I'd stop winding that motor out in neutral. 5500rpm in neutral is a good way to destroy the rotating assembly.
2) I'd put a smaller prop on and lake test. Rule out or confirm that the issue is either mechanical or an issue with set-up.

I would check fuel pressure as I have a 2000 efi 225 that would do the same because my fuel primer bulb would lose pressure go get you a Yamaha primer bulb made for the 300 and that should fix your problems

Definitely don't rev the motor up in neutral like that. You can not only ruin the motor you can also ruin your day when the motor flies apart.

Thanks guys, this has been an ongoing problem that is just getting worse and pretty sure its mechanical and not set up. As far as revving it, it don't no where jump up it levels off and then gains slowly, I don't just gun it but am sure it's not the best thing to be doing.
I did notice that it doesn't seem to be charging very good when running so I am going to check this in the morning.

I don't know nuthing about motors, but it is 32 years old. Just sayin John. Good luck.