2,000 is too low as well though, and 1500 is getting close to malnutrition levels. Taking into consideration his height and weight, he'll need more than 2,000 just to maintain his current weight.
http://www.bmi-calculator.net/bmr-calculator/
According to that, for my height and weight, I need 1759 calories a day AT LEAST. That is 1759 if I was just laying around at a constant temperature, thats what my body needs to just survive. Using the Harris-Benedict formula as outlined on the same site, the following guidelines tell us how much we should eat daily, tailored for our own height and weight, rather than a general suggestion.
If you are sedentary (little or no exercise) : Calorie-Calculation = BMR x 1.2
If you are lightly active (light exercise/sports 1-3 days/week) : Calorie-Calculation = BMR x 1.375
If you are moderatetely active (moderate exercise/sports 3-5 days/week) : Calorie-Calculation = BMR x 1.55
If you are very active (hard exercise/sports 6-7 days a week) : Calorie-Calculation = BMR x 1.725
If you are extra active (very hard exercise/sports & physical job or 2x training) : Calorie-Calculation = BMR x 1.9
I consider myself lightly active, I have a moderately physical job and do 45 minutes cardio 2 times a week, so I multiply my BMR by 1.375, and I get 2418 calories per day, to just maintain my 149 lb frame. jjam is taller and heavier than me, and his activity level is higher as well so he'd be looking at more calories for maintenance.
Using the parameters he's given us (6'4 171 lbs) I've calculated his BMR as being 1946 calories per day, and his maintenance (this bit is very assumptious, I've assumed he is my age as well, his results may be different if he isnt 22) is in the moderately active frame (exercise/sports 3-5 times a week) which means 1946 x 1.55 = 3016 calories per day to MAINTAIN current weight. If you're therefore trying to gain weight, you need to up that by about 500 a day, which puts you on 3516 calories per day, and with proper weight training you'd see a growth in your size and an increase of weight. If you're trying to cut, take 500 off of your maintenance calories, so you'd be down at 2516, and again with proper training you'd see a decrease in bodyweight and a loss of fat.
***That is all hypothetical based on what you've told us and how I've interpreted it. Doing the calculations yourself is better because you know better than any of us what you do***
If you dont see any results after 3-4 weeks (you should put on or lose 1-2 lbs in this time, depending on your intentions) then up/down the calories by a further 250 per day and carry on training, and in another 3-4 weeks check your progress again.
***Do not go below your BMR though, that would put your health at risk.***