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Back Firing when throttle closed off.

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Been riding the bike (DRZ400E great bike) once a month for over a year, purely dirt and last time out coming slowly down a hill bike started to back fire slightly. Pulled the clutch in and engine eventually stalled. Started it back up and seemed OK when on the throttle but now doesn't always idle smoothly as before. Backfiring not always happening when I took for a run after being washed. Any Ideas where to start looking for the fix?

Thanks first time forum user. :cry:

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Sounds like you have a plugged jet. (air or fuel). Or possibly the coast enrichener (anti-backfire valve) is malfunctioning.

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Carby and jetting is as standard with coast enricher still in place. Expect main jet to be 165, with bike being de-restricted by the dealer(exhaust baffle and airbox lid etc removed. Riding from sea-level to probably 500 metres.

My first suspect is leaking exhaust manifold but will check a host of things this coming weekend. Bike only just started doing this and was hopeful someone had similar experience.

Thanks for your interest and help!

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The clue here is not the back-fire by itself. It is the poor idle combined with the backfire. That indicates dirt or water in the carb someplace. Also using the bike only once a month allows fuel in the carb to evaporate and leave fuel gum (at lease with US fuels it will). It just sounds like you need a carb clean and maybe a new spark plug. Exhaust leak might contribute to backfire but not to poor idle.

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Thanks for the feedback, when I pulled down the carby on the weekend I was surprised by the amount of dirt and dust everywhere. Considering the bike has only been riden for 13 full day trail rides and the air cleaner gets redone at least every second ride this is a huge awakening to the fine dust we have where I ride. Begs me to ask the question as to whether the overflow hoses actually suck dust into the carby bowl. Anyway thanks for the help, on my first visit to TT. :cry:

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I'm pretty dusty here but I clean and use sticky filter oil spray everytime I ride. If that dirt is getting thru your carb it will get into your engine. You also might have dirty gas tank, have you cleaned the screen in the tank? Have you checked your boot carefully to see that you have a good seal on the carb?

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"Begs me to ask the question as to whether the overflow hoses actually suck dust into the carby bowl."

Odd as it may seam, the hoses do not move any air and do not draw dust in. The vents communicate atmospheric pressure signal to the float chamber and are needed for a carb to work but do not flow any air.

What you might want to check is the top cap. Often there is a poor seal there that will let dirt into the slide area.

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