well.. riding this thing stock.. simply sucks. im sorry but there is no other way to explain it sucks. sounds like a wuse too. but when u add an exhaust wow it makes a difference it roars and it goes like crazy. But i do have some issues with this thing. for one. when i changed the oil i smelt gas in the oil... and i know thats not a good thing. so i rechanged it and ill see how it does next time i change it. and 2. at a complete idle. (when all warmed up) if i push the throttle all the way in from idle to full throttle it will die. it did this when it was stock. and it does it with the exhaust pipe on. also seems like either.. not burning gas quick enough and it kind of floods itself (might explain the gas smell in the oil) or it is not jetted properly. but i dont think its the jetting cuz even when it was stock it did the same thing....

anyone else have this isse or know what or how to fix this? it only does it if i rev it quick from a dead idle. other wise if i give it a little gas then crack the throttle it will rev up fine.

 

What you are describing with the throttle is a known "quality" of the stock FCR carb. Allegedly the fuel pump doesn't hold enough fuel at one time to handle a full closed to wot fuel demand. First, I only notice it when it is idling, never had a problem once you are rolling. Second, if it is that big of a problem for you, pick up a Boyeson Quick Shot fuel pump cover, that should cure the symptom.

I'm not sure why you are smelling gas in the oil, shouldn't be a problem on a brand new quad.

 

yea like yo you said once im rolling its fine. its just from a idle to open throttle is when it does it. but i did call my local yamaha dealer and they said it might be running a little lean and that i should richen the low end fuel mixture? (or somthing like that) which is right under the carb on the right side. so i richened it a little bit but it doesnt seem like it helps much. the guy at the yamaha dealer said it will fix the "deadspot" in the throttle. is this what a deadspot is? or what cuz i richened it and it still does it. maybe i didnt go rich enough. i did check the spark plug before hand and it didnt show any signs of wetness and it did have a little white on top...
so it might have been a little lean. so maybe i should richen it up a little more yet you think?

well no, its not exactly "new" its a used 05' model but it has less then 10 hours on it total the guy said the gas smell in the oil might be a sign of gas not burning quick enough (low octane) or he said somthing about maybe it was stored for a while and gas got in it or somthing. but whatever i changed the oil. so ill wait a few days and check the oil and see how it is.

other then that. this thing is like a rocket. although its not as easy to get the front end up like it was on my old 450R guess its designed that way for a reason... racing. who wants the front end lifting up on you during hard acceleration when your racing. hehe. i kind of like it this way. that way i can go wot and not have to worry to much about holding the front down as much as i did with the honda... faster take offs = good

 

Whoever you spoke to at the dealer isn't familiar with the FCR carb. True, running lean will give you a "dead" spot, but I know from personal experience(I have 2 YFZ's sitting at my place) and what others have posted on the net that your problem is a fuel pump problem, and can be solved with the Boyeson Quick Shot. At $80.00, it is a little much for my taste at the moment. It should also improve throttle response. I actually was going to suggest gas may have gotten into the oil from storage in a previous post, but with the number of hours you say are on it, that still shouldn't happen(also a good reason to store a machine with the petcock off.) Maybe on a 2 stroke I guess.

 

Oh, and the rear swingarm/geometry WAS designed to keep the front end down and the rear tires driving out of turns and during starts, pretty cool i think. Of course, the YFZ has plenty of power for wheelies too, just not as likely to occur when you least expect/need them.

 

i called the dealer again and i spoke with another guy and he did mention that $80 peice which stops air from leaking in the carb or whatever. he said its almost guarenteed to stop it. but for $80 bucks... dang. lot of money for a tiny little thing. ill still try to richen it up a little more today and see if it fixes it any. other wise ill; just have to buy that peice. you would think when they made this quads that it includes this thing? weird. anyway. is taking the airbox lid off going to give me mich of a gain in power? i know ill have to rejet it then. and ill have to clean the filter more often too

 

I am always running in either mud or dust, so I leave my lid on. I might spring for an outerware lid later on, or just make my own. taking it off will give you more power though. That idle to wot stall has nothing to do with Yamaha, it is in the design of the Keihein carb/fuel pump. The Quick SHot allows the fuel pump to hold a larger volume of gas, eliminating the lean condition you get during an extreme demand from the engine. I don't think there is any air getting into the carb at all when this happens, it isn't like there is a leak that needs fixing. Good luck with your Yammie!

 

okay now i think im getting used to this thing more and you know what i found out.... this thing wheelies better then my Honda.. yes i said BETTER. funny how that works. when i first got it i thought wow.. thing thing is nothing like the 450r i had... it actually was hard to get the front end up compared to the 450r.... but after getting used to it. i can actually ride a steady wheelie now from first gear to high 3rd gear. (yes i know its not as good as some people can with 1st to 5th, but thats the best i ever did before) WoW i love this thing.. im happy with it, and honestly i like it more then the 450R i used to have.

but now i got another issue [img]i/expressions/face-icon-small-sad.gif[/img] i never really noticed it untill now but... it seems like it pops alot when i deccelerate. pops as in.. short smaller versions of backfires but not really backfiring... you know what i mean? it just pops alot. is this a sign of somthing? not tuned right? but one thing that comes into mind is... i used to run 91 octane right when i got it.. but just recently im using 92 octane... and this is when i noticed the poping. think that would cause it? i never poped like this before. but i dont see how using just 1 more % of octane would do it.. but thats all i ca nthink of. anyone know for sure? BTW i got new pics up!!

 

Popping on decel is a sign of a lean pilot, or fuel mix screw, or possibly an intake/exhaust leak. If it doesn't have one already, installing a Zip-Ty or similar fuel screw can be a big help. My brothers was popping like that, and we found his header was loose from the exhaust manifold. Tightened her down and solved the backfiring.

 

I GOT A YFZ 450 ABOUT TWO MONTHS AGO AND THANKS TO EVERYBODY'S FEEDBACK I'AM GOING TO DO THESE MODS; TAKE OUT THE BUFFLE FROM THE MUFFLER, INSTALL K&N FILTER AND RETARD THE EXHAUST TIMING 1 TOOTH. I WAS WANDERING IF ANYONE KNOWS WHAN SIZE JETS I SHOULD BUY?
ALSO I NOTICED THAD MY YFZ BACKFIRES ONLY WHEN TORQUE BRAKING. I CHECKED THE AIR INTAKE AND HEADER FOR ANY LEAKS BUT DIDN'T FIND ANY. HOW DO I TELL IF IT IS RINNING TO LEAN OR TO RICH?? I TOOK OFF THE ASIR BOX COVER JUST FOR A FEW MINUTES TO SEE IF IT WILL FEEL ANY DIFFRENT, BUT IT WAS ONLY LOUDER, AND MAYBE LOST A LITTLE POWER. I WOULD APPRECIATE ANY FEEDBACK. HAVE A BLAST RIDING.