would my chain being to tight slow my 400ex down?

 

depends how tight your talking about i would think. How it works on my dirt bike is if i put it to tight puts more strain on my sprockets which does put more work on engine.

 

yeah mine has no slack at all i'm thinking its too tight like it's holding motor back

 

You NEED slack ! When the bike presses down on the suspension, the chain gets TIGHTER ! Please, get some slack in there or you will either break a chain and/or do major damage to the engine drive shaft. 1 1/2" minimum slack at rest. If you want to know exactly, loosten the chain way up, take a ratchet strap and compress the rear as far as possible, then tighten the chain until it is just snug. This will give you the right amount of slack at rest.

 

I run about 1.25-1.5 inches of slack. It's a Honda but I can't see it being different.