1975 Johnson Evinrude Outboard Motor seems air starved

I have recently purchased a boat with a 1975 Johnson Outboard motor and done all of the below:

Replaced gas lines
Cleaned Carbs (2)
New spark plugs

I took the boat out this week, and it starts up strong, but seems to want to die when I take the throttle off. I am able to get it to go in forward and reverse, however, when going forward it barely goes even with full throttle. I lifted the cover a little as it seems it is not getting enough air, and it picks right up and takes off. When I bring the throttle back down and then try to get it to go fast again, it does not want to pick up speed unless I open the cover again.

Any help would be greatly appreciated.

Thanks in Advance,

First time boater

Re: 1975 Johnson Evinrude Outboard Motor seems air starved

Need to supply model #

Re: 1975 Johnson Evinrude Outboard Motor seems air starved

Thank you for the quick response. The model number is: 50Esl75b

I am wondering if maybe I have the wrong gas mixture, maybe too much oil and not enough gas? Could this be causing the problem, or does it seem like something else?

Thanks again

Re: 1975 Johnson Evinrude Outboard Motor seems air starved

Others will chime in but it sounds like if it will run with the hood off and not with it on then it may be sucking exhaust fumes thru the carb which will shut it down. Others will come in on this hopefully.

Re: 1975 Johnson Evinrude Outboard Motor seems air starved

50:1 fuel mix is correct. Might want check if exhaust is getting back inside somehow. Is possible that your to lean? just a thought.

Re: 1975 Johnson Evinrude Outboard Motor seems air starved

The air intake on that motor is under the motor tilting grab handle. It is hard to imagine anything plugging that up, but stranger things than that have been known to happen. Worth taking a look.

Re: 1975 Johnson Evinrude Outboard Motor seems air starved

If it runs properly with the hood off, maybe you have a blown base gasket, allowing exhaust to build up under the hood. With the engine running, squirt some oil of ATF directly into the carb and make the engine smoke and look for an exhaust leak. You can do this on the hose so you can get around behind it and look.