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aaronw

07 YZ450 Jetting Issues

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:crazy: Guys, fall has arrived in MI. With cooler riding temps... 50's... my bike is running ruff. Lots of popping etc when coming off throttle and down-shifting. Thinking its too lean and about just moving clip up 1 position. Any thoughts or similar issues that you fixed. Run 94 pump gas, plug and filter are good.

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On my stock 2007 yz450 I opened the fuel screw 1/2 turn counter clock wise and the bike runs alot better, less popping. it was so lean I had to give it gas to start it. try a different weight oil may help also. I have thought about the adjusting the needle clip for more top end a local yahmaha dealer mechanic opld me to move it from clip pos three to 5 or six for more top end power.

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On my stock 2007 yz450 I opened the fuel screw 1/2 turn counter clock wise and the bike runs alot better, less popping. it was so lean I had to give it gas to start it. try a different weight oil may help also. I have thought about the adjusting the needle clip for more top end a local yahmaha dealer mechanic opld me to move it from clip pos three to 5 or six for more top end power.

Moving the clip position that much is not nesessary. For a stock 07 all you should need to do is adjust the fuel screw. This is for So.Cal areas. Stock main jet, 45 pilot and fuel screw at 2- 21/2 turns. Needle clip in the stock position. If it is still lean on the bottom go to a 48 pilot at the most.

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The needle clip position controls neither top end power nor excessive backfire on deceleration. You'd be wasting your time.

Decel popping is the fault of either a lean idle circuit or an air leak in the exhaust. However, YZ450's should pop a little. If they don't pop ever, they're too rich.

The main jet controls wide open throttle fuel mixture. The needle has the most influence over throttle openings from just over 1/4 to just past 3/4. All of that is in the tuning section of your manual.

When a bike suddenly starts acting badly in response to a drop in temperature, it's usually lean. Start by opening up the fuel screw. Follow the adjustment procedure laid out Here. If you find it requires the screw to be backed out more than 2 1/2 turns, go a size larger on the pilot.

If your bike ran well during the summer, then increase your summer time main jet size about one step (165 to 168, or 168 to 170) for each 15 degrees. Understand, too, that the bike has been, and will continue to run OK with the same main jet over a certain range of temperatures. You can find one that will work fairly well across as much as 30 degrees, in a lot of cases. But overall, you'll probably have to adjust for a swing as wide as happens in Minnesota.

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Supposedly, sea level at 70, but that would make most of them way too lean. That information is only helpful in the unlikely case that the stock jetting is delivered "spot on", and of course, it's not, nor has it been any time in the last 10 years that I know of.

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Thanks Grayracer! Saved me from making some useless adjustments. I'll give the fuel screw a try and report back my findings. I will also check the exhuast fittings as well. Thanks again!! Aaron

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You will need to go up at least one size richer on the mj......stock jetting (or yours) is only good for summer temps. Cooler/colder temps dictate a richer mj.

The fuel screw will help but it will not get rid of the leaner condition due to temp changes

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