2004 Johnson 4 stroke 70 HP No High end speed

[capted1957]

New to this website.
New to me boat motor and this 2008 boat is in perfect shape as well the 2004 motor not a scratch. I got the boat and motor a few days ago. Put muffs on the motor and idle was rough changed plugs and put some seafoam in tank. The boat has been reported to have sit alot.
Put boat in water and idles alot better and nice and smooth but no high end speed. I get about 20mph out of it and the acceleration isnt what it should be and takes alot to plane it out.
I made the deal with the previous owner thinking its worth the trouble since price was right.
I suspect injectors but any ideas out there with the guys that know much more than I do?
thanks
ed

 

[clanton]

Re: 2004 Johnson 4 stroke 70 HP No High end speed

Check the fuel pressure low side and high side. This will tell which side needs repair/service. You can expect to clean the vapor separator, small filter on end of fuel pump. Pump and regulator may need replacement.

 

[boobie]

Re: 2004 Johnson 4 stroke 70 HP No High end speed

Do a cylinder drop test on it to see if you have a cylinder that isn't firing.