I picked up an '83 318 last fall which included the original 48" mower deck. I used the mower a couple times last fall and wasn't impressed compared to my old 112 with 47" deck. I didn't mess with it last year. I did my first mowing of the season last week and the day afterwards it didn't even look like I mowed.
Looking at it, it looks like the front is sitting way too low compared to the back but that's not what taking measurements off the blades say.
Today I went out and check the deck level. One thing I noticed is that with the wheels set at 2" (2nd hole from the bottom) if I set the deck level to put them 1/4-3/8" off the ground the height from the ground to the mower blades is over 3 1/2". I put the wheels all the way up and set the stop to leave them off the ground the required amount which should be 1 1/2" and it gives me a cutting height of 3" still. Quite a difference. I also measured the difference from front to back and I have the required 1/2" on the blades but the rear wheels are a good 1 1/2" off the ground while the front ones are 3/8". I just mowed again, not that you can tell from all the long grass still sticking up. Other than looking for a new model 48" or 50" deck I don't suppose there's anything else to do with mine but live with the lousy cutting.
Looking at it, it appears the front of the deck is way too low, but as I mentioned the measurements off the blades say different.