what gives

[no limit]

i have a 01 400ex, it has a rev box, cam,k&N, dg exhaust. with this stuff on it it would go about 62mph, the other day i installed my 400 kit with 12.5 piston and got the head ported. i also put a 16 tooth front sprocket. i mix my gas 70% premium and 30% 100LL now with this done the quad maybe hits 60mph. the motor is incredibly strong, runs better than ever but it just seems there is absolutly no top end, what caused this?

The 16 tooth front sproket. Go back down to 14 in the front and let her have it.

[no limit]

how would going to a 14 tooth help any?

[Jonas]

A 16 tooth front sprocket is too tall for your motor mods. I would go back to your stock gearing first. As you have indicated, the bike is not able to pull fifth gear. If the bike had unlimited horsepower, the 16t front sprocket would give the bike more top speed, but this is not the case in your instance. Gearing it back down would likely give you more top speed (on a flat surface). In my personal opinion, I feel that the stock gearing is good for even a well build 440.

Yep! what Jonas said.

[no limit]

it pulls 5th gear really strong, you can rev it out all you want it has the power to pull 5th on the road or in the dirt it just sreams in 5th but it seems like its got a 13 tooth in it thats what i dont get