late 80s 30 hp problems. help!!

hey guys I just buy a late 80's 30 horsepower Evinrude it seems to be a good motor. I checked compression in cylinder and both read right at 120 and the lower unit is good and clean no water the previous owner said he and carb rebuild seals put in lower unit and just general maintenance gone through about 2 or 3 years ago and the motor has been sitting since then until now I took it and ran it in a barrel and ran good and I took it to the water on my 16 foot aluminum jon boat and I am very disappointed in the performance I had. I had a 20 horse that push me 18 and 19 with two people and the 30 was pushin me and another guy with 2 batteries 16 miles an hour I had assumed it would push you at least 20 if not a little better with just me in it and ran 18 these numbers seem low is there anything that I need to do that can be done to get some more performance out does anything need to be cleaned I'm hoping it's just because Iits been sitting for awhile and it needs is a tune up thanks for any help

Is it running on all cylinders? Have you check to see if the prop isn't spun?

RPMs would be a big help, prop pitch as well.
Does it sound like it is running good....wide open, butterfly valve open?
A 30hp, should push 2 people around 25mph,if running right...
Weight, shape of hull, condition of prop, long shaft on short transom....lots to consider though....

thanks for the replies I am assuming that it is firing on all cylinders I guess I could be wrong but how would Icheck for sure I also do not have a way to check the RPM's but the motor seems to be running good it sounds good and the prop is spinning right I think I have had one with the hub that has come loose an this one does not seem to be doing that its on a 16 by 48 modified the aluminum jon boat nothing fancy just a plain boat

Pull one spark plug cap off when the motor is running.
Does the outboard sound different?
Put it back on and try the other cap...
Does it run different?
If you pull a cap and the motor runs the same chances are that cylinder is having trouble.It might just be a bad plug...are they new?

well I did some checking today and I believe I have narrowed it the problem down the motor is only running on 1 cylinder I took the spark plug wire off while it was running nothing happened once I took the other one off it died so I'm pretty sure its not firing on top cylinder it did however good compression so I'm not sure what it is and it also has a spark what are some thoughts of what I should check next

bad ignition coil???

swap the specific cylinder stuff one piece at a time until you find the culprit. I'd start with the plugs.