Need HELP with performance issues

Hi all,
newbie here. Been on the water plenty but just purchased my first boat, it's a 73 Browning with a 61 Evinrude 75 hp. It just doesn't seem to be running up to par, I'm an auto mechanic by trade but when I pulled the cover on this old outboard I was lost . My questions are several actually so if anyone out there can provide answers or insight to get me going in the right direction I would be so gratefull . SO here is what I'm trying to figure out...
1) why does it run better with the cover off? with the cover on it sound like it's choking out and sounds like it's missing
2)gas mileage is horrific I'm sure this ole rude is going to use some fuel but it went through probbably 20 gallons of fuel and we didn't go maybe 4 miles all said and done that alone says something isn't what it should be
3)it also has a push button gear selector unsure if that could be playing any part in the performance issues or not
4)water coming through the water disscharge hole is plentifull but it is hot is this normal or do I have an exhaust issue
5)tach is inop as well as the speedo(its broke off the back of the boat)
6)I'm unsure of the mix as well right now I'm running 50:1 is that the correct mixture
7)how complicated is it to clean the carbs
Ok I know that's a lot to put out there all at once but my daughter comes home from Iraq in about a month and I would at least like to have it running well enough to put it on the water and be able to get around a little while she's home she only gets ten days and she loves the lake so if any of you guys or gals out there can help at all I'd like to thank you in advance.
Oh and if any one has a pdf copy of a manual for this classic I sure would like to take a look at it. I'm certain there will be more questions to come but maybe this will get me headed in the right direction.
Again thanks in advance for any insight you can provide.