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So i’ve been having an issue with my 2008 yfz450, i’ve been running super lean as to where I backfire any time I shift or let off the gas or really anything.. sometimes shoot flames. Right now I have a full jdjetting setup with a 175 main jet (the biggest that JDJetting has) and I think that’s my issue as my air filter calls for a 210 Keihin. As well as the popping i’m also bogging down and completely stalling when I am on it then get off the gas, that stalling doesn’t happen all the time but when it does it seems to not want to start back up again and go unless i’m giving it gas. So my question is will a keihin main work with the rest of my JDJetting setup? I have zip tie mod done, tried adjusting my pin and have messed with my air flow screw quite a bit and even all the way open i’m still having issues so almost positive it’s the jet. Could this also be a valve cover issue? I’m not too familiar with Yamaha valves since this is my first Yamaha, should I take a look at that first or just try a bigger jet and see how that goes
 

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What is your elevation? lid on or off?
 
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