I just got a yzf450, i thought i got a good deal, 3grand. but it turns out that although it is all stock it is ALOT slower than my friends exact same one, stock and everything. I found out just this morning that this idiot didnt have an air filter and that the baffle is out, and it smokes. is it so slow because it is running to lean or what do these things run lean from the factory or what? fortunately i was able to get it for cheap enough that I have the money to fix it up. What do you think that I should do to fix it or what mods would be the best?
Thanks
Chris

 

I'm guessing you will have to tear the carb apart...while you are at it put a dynojet kit in....add a twinair filter or uni or k&n, put a slipon exhaust or better yet the whole exhaust......or return to stock

You may be tearing into the engine(check your compression) if you don't know how ask

 

Well, the first and probably most important question is....What year is it? The 2005 yfz is 10cc's smaller then the 2006.

 

If the guy didn't use an airfilter, more than likely, the engine is shot......
It is only the airfilter between dirt/grit and your motor. No filter, no protection.......

As was mentioned, you need to do a compression check. Then find out what jets are in the carb...

 

If you are super lucky the motor is not trashed. I would clean the carb, pull the head and cyl off and inspect everything, including the piston and rings if everything is OK reassemble it with an air filter and re jet it. It is OK to run it with the baffle out.

 

Hondaman raises a good point.

The first year YFZ's had the original dirt bike size motors, which were the 426cc engines. The bike was not a true 450 until Yamaha increased the bore and stroke in 2006. So, stock for stock the '06 would likely be faster than the '05.

 

Why do all that? It is not gonna hurt it any more to ride it even if he smoked the rings....but really if you want to do it right you may want to put new rings on the piston and have the cylinder honed.....riding without a filter is like throwing dirt in your engine [img]i/expressions/face-icon-small-frown.gif[/img]

 

The 1st YFZs had a 439cc motor.

 

Why do all that? Because if there is enough wear on the piston skirt and rings, the piston/skirt could wind up cracking and or coming apart into several pieces at 10,000 RPM which could cause several thousand dollars worth of damage if it takes out the head and crank at the same time.

 

Slow and smokes, plus it was run with no airfilter, time to rebuild that motor. New piston and rings, it probably needs to be bored over, and the valves/valve seats are likely worn as well. If I were in your shoes, I would get a few reputable aftermarket shops on the phone and look into a big bore kit, have them check over the head, do the oil mod, and wouldn't hurt to just replace the crank now with a stronger unit. Throw in another $300.00 or so for an exhaust system, and then go make your buddies quad look slow[img]i/expressions/face-icon-small-wink.gif[/img]