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Yamaha Tech Originally the Yamaha XT600 Tech Forum, due to demand it now includes all Yamaha's technical / mechanical / repair / preparation questions.
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  #1  
Old 8 Jan 2007
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Exhaust gunshots

Hello and a good year to everybody !!
Maybe someone can shed a light on this problem.
I have a 1992 XT600 3TB it starts good cold and warm it runs like a dream, but whenever i let go of the throttle i get some really loud bangs from the exhaust, mind you the bike does this when i let go of the throttle.
When im riding it no noise whatsoever, again it runs like a dream.
Intake rubbers are brandnew
exhaust sytem is leakproof (no holes anywhere)
Those bangs really take out the fun of riding it.
Tryed a differant set of carburettors (same type as original) but no differance.
Cecked the nozzles ont the original carb setup
primairy carb has a 130 nozzle
secundairy carb has a 110 nozzle
stationairy nozzle is an #48
Wil a bigger stationairy nozzle solve my problems ??? when i crank up the idle adjustment the bangs are almost gone,but riding with an idle rpm off 3000 revs is a bit to much.
Any help will be most appreciated !!
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  #2  
Old 8 Jan 2007
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bang!

exhaust bangs on over-run are usually due to poor combustion, ie too rich (caused by hitting the kill switch) or too lean (variety of causes, ie holes in inlet/exhaust that you are aware of. Try richening the idle mixture, There should be a pilot mixture control for the idle setting, richen it up a little, to see if that helps. on the zrx1100, there is a enrichening device deliberately to prevent over-run backfires. the bigger the cylinder capacity, the more of a problem this is for bike design engineers.
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  #3  
Old 8 Jan 2007
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my 4PT backfires sometimes when its cold, only a couple of bangs till the whole system warms up. i have an aftermarket open exhaust and air filter, and this changes the mixture a bit. its an art to tune the carb properly, mines still a little rich. it runs perfectly 99.9% of the time and then surprises me(and everyone) with a massive explosion now and then. we used to do killswitch backfires when we were kids, till you blew the exhaust off whatever old nail you were on. ah, those were the days..........
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Old 8 Jan 2007
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Hi,
have you checked the "coasting cct" on the carb? The fact that you swapped carbs probably discounts this theory but its worth a look. The primary carb has a vacuum operated valve to enrichen the mixture when you back off the throttle. On my '86 tenere the assembly (diaphram, spring & valve) has a part number of 1JK-1490A-00 and is part 47 on the diagram. Good luck,
Dave
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  #5  
Old 9 Jan 2007
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Just a thought..... if exhaust valves clearance is out of wack this could also cause backfiring.
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  #6  
Old 9 Jan 2007
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Just an idea, how about the joint between the header pipe and the muffler? I had a Husaberg 601 some years ago. That one "exploded" on regular basis until I found out that I had a bad gasket in the joint of the exhaust system.Sucked in air and that together with unburnt fuel gave a nice bang every time I let go of the trottle
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  #7  
Old 4 Feb 2007
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Yes my bangs are history !!!!
Dis-assembled the headerpipes and found out it wasnt as leakproof as i thougt, Just beneath the header clamp inbetween de cilinder en de pipe there where small holes.
Put on some better headers and adjusted the valve clearance and it works like a dream now.
tnx for all the tips from you guys !!
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