No as all the inline 6 cylinder motors are a 2:1 ration and all the small inline 4 cylinder are 2:3:1 ratio
The 1973 model, 7.5 hp Mercury outboard, requires 6.8 oz. of gear oil.
For the 80 hp Mercury, you may use any brand of gear oil that has been blended for use as an outboard motor gear lube. There are many brands available other than oem, and are specially formulated for outboard use.
22.5 fluid ounces (or 666 ml's) per our 1994 Mercury 125 outboard manual.
If the horsepower of your Mercury outboard lower unit is 75 and below, SAE 80W90 Gear Lube is recommended.
The 5 hp Mercury outboard requires no special type gear oil. General recommendation is for a GL-5 class lubricant, i.e. hypoid 90w. Most any of the oem, or aftermarket gear lubes, manufactured for outboard use, will work just fine.
outboard motor will start and idle, but dies out under load
There is no way to change gear ratios.
Mercury® Marine High-Performance Gear Lube from Basspro
motor shuts off when put in gear sometimes
The diagnostic code PO735 on a Mercury Mountaineer indicates that the 5th gear has an incorrect gear ratio. This can be the result of a broken servo shaft.
3.43 Automatic and 3.73 Manual
I had used a high performance gear lube quick silver marine lubricant it is not expensive and works very well