I have done quite a bit of reading and it sounds like the older 2 strokes have more modification options that are easier and less costly. I have the option to pick up a clean used KFX50 4 stroke (same as LT50) or an older 2 stroke LT50. What is the best choice for future modification upgrades so that it can have enough pep to keep my son interested longer than a year? Thanks.

 

2 stroke has more power, easier to mod and less expensive to rebuild..
Easy choice for me

 

I see the newer 4 stroke is about 25% larger frame and 100lbs heavier. That can't be a good thing for power to weight ratio vs the same 49cc in a 2 stroke pushing 100lbs less. I think I am going for the 2004 model with 2 stroke.

 

I had to make a similar choice when I bought a quad for my 4 year old. I was going to buy a new kfx 50 and its nearly the same size as the 90. After shopping used quads my choices were the ltr50 older kfx50 but I ended up finding a trx50 and I'm happy with my choice because the 70 is a 3 speed and he will be able to ride it longer.

Your son will enjoy whatever he gets so I guess you can't go wrong! Lol