im debating if i should go and do a big bore kit on my bike its a 2002 drz-400s with over 20,000 miles on it and i havent done anything but change the oil on it lately i did do a jet kit and full scorpion pipe on it with the k&n air filter but thats it. it still has all the original parts in it. so im debating on getting a new top end from yoshamura that comes with everything for $1,500 or if i should just leave well enough alone and just replace the plug and clutch even though the clutch is still good. cause i dont use it do do my wheelies? any input would help

 

$1500 for a top end sounds crazy, is that for a whole new head? I wouldn't do that unless your head is physically ruined in some way.

If your mechanically inclined I'd just rebuild the head yourself, you could get some oem valves, get some stiffer valve springs if you want with an aftermarket cam much cheaper then that yoshimura setup.

If you do a big bore, make sure you check the crank and make sure its good, check it with a feeler gauge to make sure its not past service limit.

I know drz400's are tame, so I don't know how long they get out of a crank and a top end.

Hell you could probably have a SHOP rebuild your whole top and bottom end for $2000.. So $1500 is crazy just for a head

 

Sounds expensive, not worth it in my opinion unless you happen blow the engine anyway =P

It isn't that hard to rebuild/upgrade to bigbore yourself either. I had no major mechanical experience before my DRZ-engine blew but by following the factory-manual real carefully and getting some help where I needed, I managed to get cylinder,piston,head all replaced.

Unless you havn't already, Start by switching to a FCR-Carb, makes a nice difference...

 

Got over 23,000 on my 07 400sm. No problems what so ever. It is really up to you but I wouldn't touch it until it blows. Then, if anything just do a cheaper big bore kit. I have a jet kit, air box mod, and full yoshi pipe on mine and it has plenty of power for me. But it is really personal preference. Good luck with whatever you decide to do

 

but by following the factory-manual real carefully