Well, I am thinking about picking up a 2004 YFZ 450 here in the next couple of weeks. It has a DuraBlue axle, Houser a-arms, and Douglas rims with Holeshot tires. I have been told the motor is stock, which is my main concern since I have heard about many 04-06 YFZ's having engine problems. I am not really sure about how many hours the quad has on it, with the way it looks I would say not many at all but looks can be deceiving.
Anyways, from what I have heard/read the culprit for many of the engine problems that the 04-06 YFZ's have seems to be be related to poor lubrication. Insufficient lubrication causing excessive wear to the piston/rod/crank/cylinder causing hundreds to thousands in damage. Looking around online I have read about many people sending their 04-06 clutch covers out to be retrofitted with the 07 YFZ 450 oil nozzle as well as installing a redesigned higher volume oil pump to solve this issue. I was looking into sending it here YAMAHA YFZ450 OIL UPGRADE
As I stated above, I do not own the YFZ yet, I have an individual that wants to trade me a 2004 YFZ 450 and probably some cash for my 2000 Yamaha R1 streetbike. The only reason I am hesitant to do this is because I have heard quite a bit about the lubrication issue that the 04-06 YFZ's have. Have any of you gotten away without doing the oil mod? Has anyone done the oil mod? If so what are your thoughts on it? Was it worth the money? Were you able to do it yourself? Also, are there any other common problems that I should look out for on this bike?