High idle and i need help syncing carbs

B

b5iveS4

Been Around the Block
I've got a yamaha xs360 with pod filters, a chopped exhaust(at my feet) and it's rejetted. I need to sync the carbs so i can plug the vacuum ports on my carb boots.
With the vacuum ports open, it idles at 3k no matter what. I hook up my manometer to the carbs and the right cylinder sucks the atf up that side of the vacuum line
pretty damn quick. So....do i need to close that air screw up a little or open it a little? I start with the air screws out about 1.5 turns or should i mess with the left cylinder
to match the right? I feel like once they're sync'd and i plug those vacuum ports, it'll idle just right but i need some help getting there. I've searched countless times and
can't find exactly the info that i need and i want to ride this sob without worrying about it anymore. Thanks in advance for your help guys.
 
Mixture screw has virtually nothing to do with carb sync.
You need to pull them back off and check the butterflies are open the same amount (they are not) the adjuster you should be looking for is between the carbs
 
On my particular flavor of carbs, an decent bench sync was to adjust the butterflies so that they all had a gap equal to the thin wire from a bread tie.
 
alright, i'll have to do that tomorrow when i've got sunlight again. I thought i had them adjusted identically before i put them back on but i guess i was wrong.
so in the meantime, can i plug those vacuum ports and raise the idle with the idle adjustment screw to keep it from dying as opposed to letting it idle at 3k?
I haven't tried that yet but i'm curious as to how it will run that way. Guess all i can do is try it. Thanks for the help guys
 
Vacuum ports need to be plugged for bike to run.
Without something in the holes, it sucks air and runs real lean
 
ok...so with my manometer hooked up, it's sucking towards the right cylinder but no matter what i do to the adjustment screw in-between the carbs...it keeps sucking to the right.
Could it be something as simple as a vacuum leak from a cracked carb boot in between the head and carb? Good thing is that it idles around 1250rpm with the vacuum ports plugged
 
It's never going to work if you have any air leaks.
A crack won't matter if it's only on the surface.
You are turning the correct adjuster?
One is for throttle stop so butterflies don't go 'over center' and cause a restriction
 
I'm pretty sure i am. Theres a bracket on the left carb with a screw in it...and then the bracket from the right carb slides in-between the left carb's bracket and screw.
When i tighten the screw i believe it's opening up the butterfly on the right carb. When i did that, it seemed to suck the atf in the tube toward the right cylinder a
little quicker but backed all the way out, it was still sucking to the right, just not as quickly. I'll take a picture of the part I'm talking about
 
099ff563.jpg


it's that bracket right in the middle of the carbs below the fuel line in the picture
 
Great pic, make things a lot easier
Yep, that's the correct screw to adjust butterflies, springs top and bottom allow center piece to move independently, screw pushed it down, spring pushes back up, top spring is to prevent screw backing off
When the vacuum is high, it means the butterfly is completely closed so air can't get through.
The left carb is getting air so vacuum is lower.
You need to bench sync so both butterflies have same gap when cable wheel is turned a few degrees
 
Ok, cool. I'll take them off tomorrow if I get a chance and give that a try. Thanks for the help. I'll let you know how it goes
 
ok, rode around for a bit today and now i have a few more questions that i'm totally confused by.
1st, i finally took it up on the highway since i had a friend to ride with me on his and I just couldn't
get it to go faster than 55 or so. It just wouldn't pull. I was sitting at like 6k rpm and just wouldn't
pull anymore. Were my revs too low to pull the bike any faster in that gear? Should i have dropped a
gear?

Also, I rode to a restaurant with my friend, then we rode to a bar and then on the way home,
the bike died. The headlight got dim and it just died when i was trying to leave a stoplight. It did it a
couple of days ago too. how far should i be able to ride if my bike wasn't charging? I feel like i've gone
further than it should if it wasn't charging at all but it's obviously not charging the battery enough.
Any ideas??
 
I pulled my spark plugs earlier today and the left cylinder's plug looked brand new like it had never been fired. I can feel air out of the exhaust but could that just be compression?
Is it possible to idle and run on one cylinder? I know this bike is nothing compared to my R6 in speed but this thing is slooooooow. Just feels like it should be more responsive and
at least quick.
 
Stator test is easy.
disconnect plug coming out of engine case, connect voltmeter on AC volts across two terminals and start it.
you'l get around 60~90V AC @5K
Just check all 3 wires as pairs (A,B,C, a-b, a-c, b-c)
Usually rectifier rather than stator
Sounds like you have either carb problems or a faulty cylinder.
white is generally lean, picture time ;)
 
You mean white on the plug? That's what I was looking for but it literally looks like I just pulled a spark plug out of a box brand new. I guess it could be somethig wrong with the coil because I'm getting spark at the points and my timing is dead on. I need to check to see if the plug is sparking to the head on the left cylinder.
 
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