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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 31 Jul 2013
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XT600e second carb

on my XT600E 2003 UK model there is a pipe running off just below the diaphragm to a black plastic device (looks like a very small in-line fuel filter) which is just floating under the seat. Removing the pipe you can blow through it without any restriction and the plastic device you can see straight through so my question is what is it and what does it do? I ran the engine with it blanked off and with a balloon over the end to see if it was sucking or blowing but no movement was seen.
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  #2  
Old 31 Jul 2013
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If I'm not mistaken, what you're talking about is the breather pipe for the carb diaphragm..
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  #3  
Old 31 Jul 2013
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Its probably a one way [out] valve to the help the slide drop when you chop the throttle thumpthump
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  #4  
Old 31 Jul 2013
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its certain not a one way valve now as i can blow through it in either direction
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  #5  
Old 31 Jul 2013
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Yeb, its a breather, just leave it.

I actually removed mine once, cleaned it, and lightly oiled it with foamfilter-Oil just to be on the safe side
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  #6  
Old 1 Aug 2013
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thanks for the info.
Not sure the two are related but a friend following me the other day said he could smell a very rich mixture every time I shut off. The bike runs very well and I'm very pleased but I'd like to know why it smells so rich on the over run. Before you ask no there is no popping or banging from un-burnt fuel in the exhaust when shutting off.
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Old 1 Aug 2013
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Rich smell

This is just a guess but I expect it is the "deceleration valve" I just read about it in my TT600 OEM manual. It is called an enrichner circuit. It is engaged when you close the throttle quickly and a high vacuum is created. This vacuum is routed to the diaphram on the side of the primary carb closing an air source to the pilot circuit. This decreased air supply will force more fuel to flow and I guess upsets the air/fuel ratio expelled by the cylinder into the exhaust to the extent that it will not readily burn and cause a backfire. It would smell rich. Now if you are always smelling rich, maybe the diaphram circuit is malfunctioning causing an over rich mixture.

Like I said, this is only a guess... Anyone is welcome to add or detract from this as we'd all like to learn here.... If I am wrong, I'd like to know it...

Steve
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  #8  
Old 2 Aug 2013
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Thanks Steve
That sound very likely as the bike runs normal with a good mixture only smells rich when I snap the throttle shut changing gear, de-accelerating, I do blip the throttle on changing down to. The diaphram was fine when I rebuilt the top end only a few months back. The set up looks as if this 'breather' pipe should be connected to something not just dangling under the seat.
Paul
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  #9  
Old 2 Aug 2013
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This must be something the newer bikes have, my mid 80's bikes do not have this. I've read about others inquiring about it. I think it just floats. Just tie it off so it doesn't flop around. This must have something to do with the later carbs that have the flexible diaphram in the secondary carb instead of the metal piston the older ones have...
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  #10  
Old 2 Aug 2013
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I'm thinking the same, my '88 just has the metal slide and no diaphram , there isn't a breather tube . Other carbs I have with the rubber diaphram have the tube going into the airbox.
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  #11  
Old 3 Aug 2013
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I am interested in the resultant effects of this topic. Occasionally, and particularly when it is hot, there is the smell of petrol when the bike (2001 XT600E 4PT) is ridden in a spirited fashion, i.e. lots of acceleration/deceleration. Friends following me have remarked on it and once or twice I have smelled petrol after stopping following a good run. It happens infrequently and there have been no other signs/symptoms, e.g. no carb overflow, float height appears OK etc. The bike runs faultlessly with no fuelling issues. I guess it is one of the quirks of this particular type of carb which should be savoured, as long as it doesn't get worse, or course.

I remember my Dad telling me of one of his bikes, an old Panther, which used to weep fuel and which went up in flames one day whilst he was sitting astride it talking to his brother. Jerry Lee Lewis's "Great Balls of Fire" springs to mind!
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  #12  
Old 3 Aug 2013
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Am going to try a heat shield plate between the carb and motor. The heat from the motor I think sort of cooks off the gas and that is where the smell comes from. With the heat shield the carbs may not get as hot , and hopefully start better when I attempt to start it hot, ( restarting after engine has been run just a couple minutes earlier).
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  #13  
Old 5 Aug 2013
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Glad I'm not alone on this one then 'pusser65' that is exactly the symptoms of my bike, I get a whiff of petrol sometimes when I switch it off after a spirited run.
Maybe it is just the characteristics of the model.

Paul
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  #14  
Old 5 Aug 2013
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Keep us posted on your heat shield idea, may be a good one! It would be nice if it helped the "hot start" problem we face from time to time.
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  #15  
Old 6 Aug 2013
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Will do, mine if it is hot and I shut it off, I can start it within 2-3min fine, after that I have to wait 15-20min to even bother depending on how warm of a day it is. I scared the heck out of some people at a gas station a couple weeks ago. It had been about 5minutes and I decided to try. The first kick she banged like a rifle going off against the building and metal canopy. Kicked it ten-12times didn't even attempt to start ,then parked it for 10minutes, started the first kick .
I once in a while will get it to go with a little bit of throttle while kicking, but most times it is just dead.

Top of the line 80's technology.
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