Rough Running 07 YZ450F

My 07 YZ450F is running pretty rough… During the 30 minutes of break in, the bike sounded and seemed to run great… On my first ride the bike sounded poppy on the bottom end. Top end seemed fine. I pulled the spark plug and it looked tan and on the lean side. The inside of the end of the muffler is black as night with carbon. The bike back fires sometime when I crack it. There also seem to be a ticking sound in the top side of the engine.

I thought maybe the jetting was off because of the poppy sound… Now I’m thinking the timing may be off. Any thoughts on this problem?

you shut the choke off? maybe you plugged the pilot air jet up with filter oil.

i once had a similar problem on my bike, is it possible there is dirt in the carb?

Hows the weather in Georgia? I bought my '06 this time last year and I remember it popped like crazy in the cold temps. Other lucky new owners experienced the same. I richened up the pilot at the suggestion of another TT'er and adjusted the fuel screw and the bike now runs great and plug looks good. Sorry, i don't remember offhand what it is now but i went up one or two sizes.

Hope this helps.

Go with a richer main jet, maybe a 170, and get a Zip-ty fuel screw, and make sure it is properly adjusted. My factory fuel screw fell out in the 1st 15 minutes and it ran REAL rough until the dealer finally figured it out. With the Zip-ty or other brand with external knurled adjuster knob, you don't have to worry about that so much - it's quite obvious if it falls out!

...I pulled the spark plug and it looked tan and on the lean side. The inside of the end of the muffler is black as night with carbon.

Remember that the color of your spark plug tells you nothing about jetting on 4-strokes that use unleaded gas. Your muffler will always be black.

This is my plug and I'm running rich with 48 pilot and 170 main. White as snow.

DSC00639.jpg

My 07 YZ450F is running pretty rough… During the 30 minutes of break in, the bike sounded and seemed to run great… On my first ride the bike sounded poppy on the bottom end. Top end seemed fine. I pulled the spark plug and it looked tan and on the lean side. The inside of the end of the muffler is black as night with carbon. The bike back fires sometime when I crack it. There also seem to be a ticking sound in the top side of the engine.

I thought maybe the jetting was off because of the poppy sound… Now I’m thinking the timing may be off. Any thoughts on this problem?

My 07 did the same thing. Afetr about an hour of break in I put a white brothers system on it and it went away. The stock exhaust is garbage.

My 07 did the same thing. Afetr about an hour of break in I put a white brothers system on it and it went away. The stock exhaust is garbage.

I don't think you could fairly say that the stock exhaust is garbage. It may not be as good as the aftermarket stuff, but show me a bike that has a better stock exhaust than the YZ. Obviously the Honda twin pipe attempt was a failure. KTM maybe, but don't they use Akrapovics as stock? But that is an aftermarket company doing OEM stuff, so it doesn't count. You could pay an extra $500 for the YZ and they could have an OEM pipe, but they probably decided it was better to keep the price down and let people put whatever they preferred onto their bikes after buying them, since everyone has their favorite.

Either way, I highly doubt that the stock pipe is the problem. In your case, kx256, more than likely the easier breathing of the WB changed the jetting enough to make your bike run better. I would place the problem as fuel screw adjustment and/or jetting changes. Remember the factory jetting is a baseline, not a universal correct setting for all altitudes and humidity and all the other factors. So look into what the best settings are for where you ride and try it out. It can't hurt.

Remember that the color of your spark plug tells you nothing about jetting on 4-strokes that use unleaded gas. Your muffler will always be black.

This is my plug and I'm running rich with 48 pilot and 170 main. White as snow.

DSC00639.jpg

sorry thats just wrong. The ceramic portion of a plug will always read correctly. If that plug is white on the ceramic, you are lean on that plug. It does have a hint of tan to it but it looks washed out from a flash.

The reason the silencer looks black and the metal portion of the plug looks black after a while is from the AP circuit. It dumps a huge amount of fuel in the cylinder and not much of it gets burnt. Thus the excess carbon on the metal. Always read the ceramic.

sorry thats just wrong.
I disagree. The lead in the fuel is where most of the readable color comes from. The color of the plug shell means nothing as far as jetting is concerned, either. A plug run in unleaded fuel will look white on a clean chop at under 12:1.

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