Hi everyone, I am new to this forum and would appreciate any help that you are able to offer. I own a 2005 YFZ450. Mechanically, it is completely stock. I have it serviced regularly and up until last weekend it has been trouble free. My problem occured mid ride. The quad lost power all of a sudden about 15 min into the it. It lost all power down low and wont idle properly. When rolling down a hill for example in gear without the power on it backfires severely through the exhaust. Also feels a bit sluggish everywhere in the power range. I inspected the air filter and it is fine. Tried running the quad without the air filter but no difference. I removed the bowl from the carb and cleaned the jets aong with the addition of a fuel filter hoping that a bit of foreign matter entered the fuel system. This didnt make any difference.
Has anyone encounted this problem? Or able to point me in the right direction?  

could be a timing problem, there's just too much unknown at this point.

try wiggling the switch on top of the carb. it could have gotten stuck.  

Thanks for that. I will have a look and let you know.  

I believe that the float level may be to blame. Can anyone help me out with some hot tips on getting the correct measurement. In the manual that I have it says 8mm from the face of the carby to the top of the float. Is this what other people use. I am having difficulty getting the correct measurement. Any info will be greatly appreciated.  

Wolf1,
I have checked the voltage output from the switch at the top of carb and it is ok. I don't believe the timing is the issue as it runs a stock cdi and none of the timinf gear has been modified.(unless you are aware of some dramas with these???)
thanks.  

have you checked the diaphram in the top of the carb.
inspect it for holes or wear.

this would explain the sudden loss of power and rough  idle.  

I had this problem on a Polaris.  It was valve clearance.  

Hey guys,
I took the YFZ450 to Yamaha after having no luck at home. They have informed me that the timing was 4 teeth out! No one has touched the timing recently. Is it possible for these motors to jump teeth? Also the mechanic told me there is signs of a loss of oil to the top end, namely the cam face and lobes in the head. I fing this suprising as the oil is changed every 10hrs and the valves shimmed every 20hrs.