you'll definitely have to tighten it up more, but you will have ample room to tighten it up and adjust the chain as it stretches. let us know your results on your 14t sprocket. Im totally happy with mine.

 

Get sparks racing timing advance key for 15 as said before. My bike kicks it up the hill great. Why are you people even talking about riding your quad in first geart. I don't even use my first gear. your not supposed too, 2nd is low enough

 

I too put a 14 tooth front sprocket on my 400EX, then for giggles I added a 39 tooth rear sprocket (since there's enough room on the chain and I got it for $10.00). It stinks, don't bother, makes first gear and second gear almost the same. So I put the stock 38 tooth rear sprocket back on.

 

Maybe 2nd is low enough on the MX track, but in the woods riding around obstacles and trail-blazing, sometimes you need a low 1st gear.