1976 15HP Johnson won't throttle, idle, or start easy...help!

Ok, so I know that sounds like a lot, but here's the story. I bought this motor and it fired up great on the muffs. Idled fine low and could rev it up. Brought it home and it was the same thing. I changed the lower unit oil, and filled up gas (91 octaine NO ETHANOL), and mixed in 2% (50:1) Prestone synthetic 2-cycle oil. I put the motor on my 14 Klamath I just restored and took it out to the lake.

After pulling the start cord a few dozen times, and adjusting in the choke knob and idle speed knob, I finally got it to start, but the would only run for a few seconds then die. Eventually I got it to stay running, but only at full throttle, which was probably at only 20% of the speed it should be. This too would soon die out and then it would take time and lots of cord pulls to get it running again.

Does anyone have any ideas? Sorry first time boat owner here. I am pretty technically cable of most repairs but have never worked on boat motors. Is it time to take it in to a pro?

Thanks in advance for any suggestions!

Re: 1976 15HP Johnson won't throttle, idle, or start easy...help!

First Check compression and spark.
You can find out how to check compression by reading the first thread called secret files up the top of the forum page..
Check spark by grounding each plug on a good metal contact on the engine (away from the fuel coming out the sparkplug hole) and pull the starter.
A motor thats very ill will run fine on a muff as there is no back pressure to work against it.
Yours could be something serious or just something small, these tests will narrow it down
A compression tester is very handy and is about $20
Dont take it to a pro yet as this is what they would be doing but charge you a lot more than what a compression tester costs

Re: 1976 15HP Johnson won't throttle, idle, or start easy...help!

I would also get an open air spark tester and see if the spark will jump a 1/4" gap with a blue flame and snap. Spark may be too week to fire under compression. Others will chime in about points and coils and how to set them and also how to check them. Good luck