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Can't get 08 450 started

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My 08 450f just won't start. The valves are good, good compression, checked for spark and cleaned the carb. It will run just fine when I bump start it but I just cant get it to kick start. Don't know what else to check other than the CDI box. Any other suggestions would be great, I am new to 4-strokes so this is very frustrating.

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If you have compression, it's either ignition or fuel. Swapping the box is easy enough, but if you don't have a friend with a kx450, check the spark by pulling the boot and check the arc against the engine. You can stick a Phillips in the cap and while holding the handle, hold the shank close to a bolt. If you pull the plug, you can crank the bike with your hand.

This is not a sure test, as your spark could still be weak, so getting your hands on a known good CDI is a better test.

Also, check to ensure your flywheel did not slip. I have seen keys bend or break, so that's the second ignition test. If you have spark at the plug, your stator should be fine.

On the fuel, make sure you have free flowing fuel from the tank into the bowl. If so, then check the bowl. I had a little piece clog my main jet once on my kx500, and the bike would not run. It would start, but not run. You can also have the same thing happen with the pilot, which could keep the bike from starting, so check your jets by shooting carb cleaner from a can through each jet.

Are you assuming your valves are in spec or did you check them after the problem started. If you have not checked them after the problem appeared, it's worth a quick look, as this eliminates a simple issue quickly.

Good luck.

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The bike does have good spark and compression and the carb was thouroughly cleaned. The valves were on the low limit on spec so I did adjust them. Still nothing, haven't got at the flywheel yet. I do get the bike to backfire when trying to start so I just don't know. I appreciate the help though any suggustion is definetaly helpful.

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  • 3 weeks later...


Good compression

Good Spark

Put in new top end

New spark Plug

Cleaned Carb

Timing is right on the money

Fuel Air screw is right on spec

Get the bike to back fire with a couple kicks

Wiring harness looks good, no corrosion or wrecked wires

Still NOTHING wont kickstart. Will still bumpstart and run fine with that.

Dont know what else to check running out of options. Have read about 2007 bikes with the same symptoms and a new flywheel did the trick, but I just dont know. Dont want the bike to beat me.

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  • 1 month later...

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