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Hey Guys,

Recently I noticed when accelerating up a slight incline with my 400, as soon as I back off the throttle, I get this small back-fire out the exhaust. I was wondering if this is a symtom of tight valves or incorrect TPS setting? Has anyone else experienced this. Just asking.
 

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I get small back fire once in awhile too.
Even on the centre stand, rev up to around 7000/8000rpm,
let go the throttle and it back fires sometimes.
 

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A occasional backfire is very characteristic of a single cylinder engine. I've owned several. The larger, the engine, the more prone it will be to do this. Twin cylinders also do it, but less frequently. Both my AN650 and DL1000 occasionally pop through the exhaust on deceleration. It is normal on deceleration.
 

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I found this on a google hunt:

Question: Why does my bike backfire?

Answer: In general, backfiring on deceleration (as opposed to acceleration) is generally caused by a lean condition in the pilot circuit. What happens is that the mixture leans out enough to where it fails to ignite consistently. This, in turn allows some unburned fuel to get into the exhaust pipes. Then when the engine does fire, these unburned gasses are ignited in the exhaust pipe, causing the backfire. Newer carbs have an 'enricher circuit' which cuts in on deceleration to help this problem. Earlier carbs don't have this. Check the pilot circuits and set them a bit richer. It is hard to do this right without some equipment to test where you are. Aftermarket pipes often increase backfiring, probably because they make the bike run leaner. Some backfiring on older models is par for the course, so these owners should learn to enjoy it.


I realise most of you have FI but the same must apply particularly with the search to map to achieve lean burn/environmentally friendly conditions.

Interestingly mine does not backfire - maybe its running rich?

Regards
 
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