1973 Mercury 9.8 110 running issues

[bigcatchstarn64]

I have just recently gotten a '73 Mercury 9.8hp 110 outboard motor. I replaced the broken venturi in the carb and replaced the impeller. Once I did that it turns over quite nicely and runs descent. Only a few problems with it. It will not idle in neutral, nor while in forward will it stay running with low throttle. While in Neutral and at full throttle it seems to run super wide open and sound great! But while in forward at full throttle it seems at like 80%. Spark plugs are both warm if I cut off the engine at full throttle so that tells me both coils are ok, right? I heard that the position of the angle on the motor on will make a huge difference in the way it pushes the boat? I have a 9.8hp on a 16' flat bottom alumicraft and I feel it should push me more than 7mph. Also, the gears seem to be off because in the Reverse position, it is in Neutral and while in the Neutral position it is really in forward. And there is no Reverse. Any suggestions would be helpful and I was thinking of getting a manual but unsure if they really do tell you everything about everything and how to fix stuff and the correct settings for everything. Thank you!