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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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Old 28 Nov 2007
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help with carb synching

I have an 1984 xt600 US model. It has the two barrel carb. The one with the CV secondary.

The Clymer manual says to

1. open the primary .20inches
2. adjust the synch screw so that it just makes contact with the secondary linkage
3. when the primary is fully open the secondary air valve should be horizontal.

Problem is that when I set the synch screw to where it just touches the linkage, the secondary air valve is way past horizontal at WFO.

If I set the synch screw so that the secondary air valve is horizontal at WFO on the primary, then the linkage does not make contact until 1/2 throttle according to the primary slide.

The secondary shaft is fixed and the linkage has no adjustment. Nothing is missing and not worn out. Bike has 5500 miles on it.

If I set the synch so that the air valve is horizontal at WFO(and secondary not moving until 1/2 throttle on the primary), Im assuming Im going to get a big bog.

What is more important? The timing of WHEN the secondary air valve moves or its FINAL POSITION at WFO?

Thanks in advance.
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Old 28 Nov 2007
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there is more info here


hope this helps

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Old 28 Nov 2007
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Goofy thing is that the bike runs fine. I just took the carb off to replace the bowl gasket. I noticed that there was a synchronization section in the manual. I decided to see if mine needed adjustment. Thats when I noticed how far off the air valve was at WFO. Im just wondering if I am losing some full throttle performance by having the air valve significantly past horizontal.
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Old 28 Nov 2007
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if it aint broke............

Originally Posted by tx246 View Post
Goofy thing is that the bike runs fine.
if you were happy with it, and it zips along nice, leave it alone!
the old saying "If it ain't broke, Don't fix it" still holds true ya know. I for one should heed my own advice here, cos' im a "fiddler", i love taking my bikes to bits to see how things work or just to check stuff. sometimes I make things better! sometimes I makes things worse.............

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Old 28 Nov 2007
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Im assuming it runs ok as this bike has never been synched since Ive owned it. Its just that I cant adjust it in a manner that the manual calls for....not even close. At WFO the secondry air valve blocks at least 25% of the available surface area which doesnt make sense. Im going to synch it like it says in Auke's post and go from there. I think I can get at it without taking everything apart if it doesnt work out.
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