Yfz 450 Not Getting FUEL / Too Lean HELP


Hey Guys,

Have a weird problem and don't really know what to do, curious if anyone has seen this.

I have a 07 YFZ 450 that has the Cam Mod and a NMotion Exhaust it has been jetted with a pilot of 45 (Stock is 42) and a Main of 172 (stock is 155). When I get on top end it start bogging and spuddering, when pull in clutch it dies and has to sit for a few.

What I Did to get it to run:

1. First pulled out the spark plug an it is white, from what i know that means to lean. Put the lid on the air box, no change.

2. Put a 190 Main and a 50 pilot : No Change

3. Raised the needle all the way up, lowest clip postion #7 : no change

4. Took the bowl of the bottom of the carb to see if how fast fuel was coming into the bowl... SMALL SMALL trickle actually a broken stream of fuel.. Blew out the where the float sits and fuel comes in now have a steady small solid stream.. AND CHANGE to a colder plug. Fixed the problem i thought....

After that with the Needle all the way and a 190 Main i would think it would almost foul plugs but it still looks pretty lean... it does run and haven't had any problem for the most part... still spudders a little in 4th and 5th at wide open throttle...

Has anyone seen this... I just can't believe that this is correct, but i don't know what to do about to get more fuel.

Think i should remove the carb and break it down and clean it really really good?

Thoughts and suggestions welcomed and needed:

Check two things:

1) your spark plug gap - I was diagnosing the exact same thing on my YFZ, and changed the plug. Once I fixed the problem, I still had another problem.....when I put the new plug in, I just literally dropped it in the hole and tightened it down. I closed the gap almost completely. Took it out, regapped it, good to go....

2) Take the vent hoses off of your carb. (there are two, tied together.....they are small like automotive vacuum hoses. With some compressed air.....blow them out. I'll bet one or both is clogged. I had the EXACT thing kick my ass for a few days. Bike would run as long as I wasn't WOT, or near WOT. A friend suggested I check those vent hoses......sure as hell, one was clogged full of mud.

I was amazed.......I was fearing having to take my quad in to a shop, and dreading what might be wrong. Thanks goodness I have friends that are knowledgeable. :bonk:

k, Did try a new plug... a colder one... I can blow threw the two lines pretty good, by mouth (Sounds bad, heeh).. I haven't tried to compressed air... Try that this weekend...

Also, just found out that the guy i bought it from ran AvGas in it...Not sure if that has anything to do with it or not...

OK, I now it sounds funny but I had a customer with the same problem. It ended up being the needle and seat of the carb sticking and not letting enough fuel into the carb under hard excelleration. Check it out first before doing anything else, it free.

Not sure I know how to check that? Can you provide some helpful hints? I know how to get the needle out and change position but how to get the seat and determine if it is sticking i don't know.


He's talking about the needle/seat for the float level. I also agree that sounds likely, since once you get the motor on top of the rpm range, it's starving for gas, not so much the ratio, but instead the amount. If the float is too low, or the needle is sticking closed (even sporadically) then the bowl won't ever be full enough to allow banzaii runs through the gears. Your white plug and super-rich jetting also suggest that it's not the fuel ratio, but rather the fuel amount. BMWDoc had a great idea as well, if the vent lines are plugged, the bowl level will be low or non-existant as well. I've had the float needle stick closed many times from not riding, so I strongly suggest you remove it, gently sand the aluminum edges smooth with some 400 grit sandpaper, then check to make very sure it's not hanging up in the bore. Inspect the condition of the Viton rubber tip of the needle, then blow the seat out with compressed air. Once you have the needle moving freely and the vent lines perfectly clear, check the float level. I turn the carb upside down, then check to see if the float is level with the bottom of the carb bowl mounting surface. Then GENTLY lift the float away from the springy needle and allow if to rest on the needle, checking for free movement the whole time. If all is well, re-install the 172 main/45 pilot and test ride. I really think that jetting setup will be fine for you. If it's not, then you likely have other carb or tuning problems. BTW, have you done a quick check of your valve clearances? Not much worse than rejetting the carb for weeks only to find out the valves needed attention...

You hit the nail on the head zookeeper...

Thanks ZooKeeper and T-Rex... I will give that a check tonight... Hopefully get to ride it this weekend to test. I did have the values checked and they are in spec...

Thanks for the help and info. This bike has been sitting... it is an 07 with about 10 hours before i bought it

Thanks again

Just a side note, make sure to do proper maintance. Oil changes with very good four-stroke motorcycle oil. I use Amsoil oil in all of my four-strokes.

I didn't realize it was sitting so long. I think zoo and the others probably are likely going to be correct, with the needle being stuck. That will be common with any carb'd motor of any kind. Just take your time and remember how everything came apart......take pictures to document if you need to refer back to them.

Fwiw, I have close to 400 hours on my 2008 YFZ. I've used nothing but Yamalube and Yamaha oil filters.......and I change it about every third ride. I haven't touched the clutches, or anything internal.....except to do the cam mod, and check the valves several times. Runs like a champion......couldn't ask for any more. :bonk: Maintenance definitely is your friend....as it has shown me.

you could possibly pull the petcock out of the tank and see if it can b stopped up with trash cause the petcock has to screens on it one on the main pickup and a shorter one on the reserve

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