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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 11 Aug 2013
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Backfire on overrun

Hi folks. Just bought myself an xt600 3aj and absolutely love it. Ive had a general mix of bikes xv1700, fjr1300, triumphs, fj1200 etc etc etc and recently decided I wanted an 80's thumper and wish I had done it years ago. One I bought is a good example. 53k on clock, runs great. Only issue I have come across is this almighty backfire when closing the throttle on overrun. It only does it if the revs are high when you shut the throttle. If I decelerate gently it is ok. Iv'e given a few pedestrians a severe shock when passing them as it really is quite loud. Any pointers greatly appreciated.
Thanks
Angus.
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  #2  
Old 11 Aug 2013
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There is a diaphragm on the left side of your carbie (coasting enricher) its a small dome about the size of your thumbnail held by a couple of screws.

Take a peek behind (watch out for flying spring) if that is worn/split it could cause your symptoms, its purpose is to prevent popping under decel.



Mezo.
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  #3  
Old 11 Aug 2013
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An leaky exhaust-system will do that aswell, so make sure all connections are tight
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Old 11 Aug 2013
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Check the intake boots, maybe sealing ring is not good.
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Old 16 Aug 2013
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hi there as mezo says its proberbly the coasting enricher diafram once you have removed the small cover on the side of the carb carefull of the spring remove the diafram and check it for holes etc . under the diaframe on the carb body there will be a small brass pin/plunger there will be a very small screw at the side of it . this pin/plunger must move in when you press it, it is spring loaded so will move in and out. if it does not move the internal plunger is siezed . undo the screw you will notice the carb body is slightly peened over on to the plunger bit , see the two small marks . grab the bit sticking out and pull to remove but if its siezed bad you could have a problem dont forget the plunger/pin is brass. it may be possibal to get some wd40 etc down the side of the pin/plunger to free it off if you are unsure get someone to have a look . then just clean it all up and put back together ,no more back fireing . good luck zigzag
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Old 17 Aug 2013
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At least the US version comes as a kit with the diaphram and the brass valve. I just rebuilt 2 sets of carbs and replaced the diaphram and brass valve assy. It should come out fairly easily. Mine was not seized but did have the two marks on the valve. I think this may have been part of the assembly process. I did not find it peened at all. I was able to grab a hold of the brass valve on the lip sticking out and wiggle it out.
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Old 22 Aug 2013
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Thanks for replies guys.Much appreciated. I will investigate this weekend.
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back fire... sidecarmx Yamaha Tech 7 25 Sep 2012 23:08

 
 


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