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2007 YZ450f Won't idle, and backfires

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So I have a 2007 Yamaha YZ450f that I bought a few months ago. I took the bike out to desert for the first time, it was running PERFECT I was riding it for about 30 minutes and then all of a sudden it just started popping and was backfiring no matter what RPM I was at. I came to a stop and it just died, I started it up again, and I found the only way to keep it alive was by using the throttle. When I got home (sea level) I looked at the carb and noticed that the fuel screw fell out and was MISSING! I figured it must have fallen out while I was riding, So right away I bought a new Factory Effex fuel screw. When my new fuel screw arrived I installed it, and adjusted it 2 turns out. When I started the bike up with the new fuel screw, NOTHING CHANGED the motor wouldn't idle unless I had my hand on the throttle and was constantly backfiring on every RPM. So now I have the carburetor removed and taken apart, I could clearly see all the jets were clear. There is one thing that I noticed, a piece inside the carburetor was chipped off. When I took apart the carburetor the chip never fell out so I'm assuming whoever was working on the bike last must have dropped the carb and chipped it. After that I unscrewed the sparkplug, the sparkplug came out WET with fuel, figure this is due to such a rich mixture. I'm beginning to think that when the fuel screw fell out a piece of dust may have gone in it's hole and gotten into the circuit.

Here's a picture of that chipped piece I was talking about. 

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The fuel inlet needle looks good

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Ignore the chipped piece.

It sounds like your timing chain jumped a tooth, or your stator failed.

If you have not changed the 10 year old timing chain and tensioner, don't ride it till you do....and inspect the cam timing.

If it jumped more than one tooth, then you have bent a valve.

Jetting requirements do not change for no reason, and never at all rpms and throttle positions at once.

 

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Okay guys so today I pulled off the cam cover, I set the crankshaft to TDC and it looks like the camshafts are in time. I should also add that before I bought this bike, it was sitting for a few months, and I'm using the same old gas thats been sitting in there for that time could this be the issue? I'm going to order a carb rebuild kit that has the stock jetting, previous owner put in a size 50 pilot jet (stock is 48)20170416_145115.jpg.8dce2d7b1ffa7a8e5bc158e8d23051ab.jpg

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Okay I don't see any green corrosion, but I'm going to clean out all the circuits in the carb, after that I'm going to drain out the fuel tank and refill it with fresh 91. My carb rebuild kit should show up at my front door sometime around next week, and on top of that I bought a new spark plug

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Okay so the Carburetor rebuild came in, I went ahead and rebuilt the carburetor, I cleaned off the old spark plug, drained the old fuel tank and refilling it with fresh fuel. I threw the bike all back together and started it up just now, and for once it would idle!! It was holding an idle without me giving it gas! So after the bike warmed up a bit, it was still acting funny but not as bad as before. Lots of popping, and I noticed when I would rev it up and let off the throttle, the rpms would be very slow to come down, isn't this called rev hanging? Anyway I heard that it is a sign that the A/F ratio is too LEAN, so I started enriching the mixture by unscrewing the fuel screw (Passed 2 full turns). I unscrewed it about a turn and a half from where it was, and then the popping went away.. I gave it a good rev and the rpms rised and fell just as they should. Bike is now running PERFECT, THANK YOU

Edited by 450cc's of brapp

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