Marine: Boating, Sailing, PWC, GPS and Navigation - 1970's johnson 115hp outboard throttle/gas

Ok, I recently bought my first boat. I took it to a boat service shop got it all checked over got my 110psi for compression. Everything was all ok.. i even had a wow. So I take it out to the lake to give it a go. It wont start. Hauled it back home and took it back to the same service shop. The electrical box was gone so I was not getting any spark. Ok, two weeks later it was finally done. Alright I finally get to take it out and it should run. Got it to the lake and put it into the water... and it started right away. Left my warm up lever up till it was high idling and dropped it down. Put it into forwards and it was going alright... gave it more throttle and went faster... but about half water open it just wouldn't go anymore and would not speed up anymore from half up... but it was trying to give it the gas.. popped the motor cover and seemed to move all the way.. sometimes dropping the throttle it would stall. Not too sure what is wrong. For a 1976 banshee it should to flying with a 115hp johnson? Like I wasn't going even close to the speed of pulling a tuber or water skiier... Anyone have a answer to this question? I forgot to prime the gas tank before starting but it started fine if that has anything to do with it.
Thanks in advance. Derek

Welcome to the board.
I understand the frustration of a short boating season and a long wait for service, just bear with the service shop if you end up back there. We have been 2 weeks out for about 2 monthes, but it doesn't pay to have another tech just for the summer.

As far as the motor not reaching full rpm I can give you a couple things to check.
First check the spark plugs it they are not new change them, don't clean them, they are cheap and I've chased a running issue more than once just to have a bad plug.
Pull the cover off the air box and make shure the throttle plates are opening all the way.
What size is the prop it should have a 14x some # and how long is the boat.
Has the boat sat outside without a cover? The wood in the boat can absorb water and cad add a lot of extra weight to the boat.
When trying to run at full throttle on the water have someone sit in the back and try to pump the primer bulb this will eliminate the fuel pump.

Thanks Samuari, as far as the spark plugs they are all new of this year. The boat has always been tarped and has all new interior. The air cover... i know there was a spring missing they said and i put one on there.. but it may have failed. It wasn't closing and opening good before i put the spring in... i have not checked it since. The weather has been bad here. Thanks for the information. I will try the primer and check to see if it is choking right still. Also get back to you on the prop.