The mrs always said carbs were bad for me...

Hey all, so im struggling with my xj650.

Throttle butterfly in closed position.
Bench synced carbs as per instructions.
Noticed the butterflys are in sligjtly different positions.

What are the 3 tiny holes on the inside top of the outlet side (engine side of carb) and the jet unit thing on the left side in the outlet side?

Asking so i know where the butterflys are supposed to be located, and to understand how these buggers work as the diagrams etc that ive seen dont show clearly whats going on.

Thanks

 

3 holes is how fuel gets in for the pilotjet and mixture screw circuit

these photos will help
Something New, Something Naked

 

some more reading for you
THE SECRET LIFE OF CARBURETORS

this is some very heavy reading
http://www.zrxoa.org/webpages/techinfo/carb/carbtuning.html

 

The purpose of a bench sync IS to get all four butterlfies visually at the same position, with the help of paper clips or business card strips slid at the bottom of the butterflies. If you can claerly see that they are not all even, you should do it again properly, otherwise you'll be out of sync by far when you'll start the running sync.

 

...or even by just looking at the butterfly's relationship to the hole that is closest to the engine side of the carb.

 

this link explains what you are really doing when you sync" the carbs
TALKIN' TECH: Various thoughts on various issues

 

these are the holes you're looking at

turn the idle screw in until that back hole is fully exposed on #3 carb, then another 1/2 turn.
then use the sync screws to make the other carbs look like #3. judging the distance from the hole to the butterfly plate.
now turn the idle screw out a bit to reduce that distance but not completely and closed. redo the sync screws to make them all match
that's it, your bench synced
here's another carb from the same rack

 

Polock is correct. You have to start with number 3 and make the others exactly the same. I use strips of a cut up business card, then set them to drag or feel all the same resistance when you pull the card strips in and out.

 

I have in most cases put the carbs on like that, filled them with gas and had the bikes fire up and idle almost perfectly. The other key to that is to wet set the floats off the bike. I made a jig that holds the carbs similarly to how they sit in the the bike. Level and square. I also made an I V bottle like fuel tank to test run the bike with no tank in place while syncing and adjusting mixture screws.

 

Having trouble with carbs? You could try the keto diet and cut back some... oh, wait.

This might help. See page 19 for the explanation you seek.

Inside Your Carbs

 

Thanks everyone gor all the help. Am still reading but its all helped sooooooo much!

Im gunna pull the carbs again tonight n take a look.

I bench synced them the other day by using the paperclip method. However even tho the butterflys are the same at the bottom, they are not the same at the top (in relation to the tiny holes)

Will retry by aligning them with the holes and see where that gets me.

 

Bench sync retried by using the rear hole as a locater. Then matched the other carbs to it and all good!
Checked and made tiny tweaks to the float heights as needed. Also found that number 2 carb float post has been dammaged and repaired.

Will recheck the bench sync tomorrow and then check the float heights using the clear tube method.

Fingers crossed and will keep you updated...

 

Ok so got her all setup. Back together and still no joy.
1.5 turns out and too rich on 234. Cylinder 1 is waaaay to rich.
Mild anmount of black snoke from exhaust so i know its gotta be rich.

From cold with no choke shes idling. Ish.
Same when she starts to warm up.


Im not sure why in getting this problem but its driving me batty. Any thoughts?

 

1.5 turns it should be 2.5 turns if your talking about the mixture screw.
if you do not have a color tune you can set mixture by temp if you have a temp probe you will at least get them all to the same setting.

 

you should verify the position of the air jets under the diaphragm, smaller goes towards the engine like this
http://www.xjbikes.com/forums/threads/a-journey-through-a-hanging-idle.74268/page-7
make sure when the choke is off that the enrichment plungers are down all the way.
check the condition and placement of the little o-rings on the mixture screws.
were the carbs level when you set the floats, on the bike makes the floats too high

 

Air jet positions are ok. Already checked theyre the right way round.

Enrichment plungers are down but ill recheck them tomorrow with the mixture scrrw orings.

Carbs were level, had to use garage floor and level the carbs against a box but it worked well.

Will head scratch some more and report back.

Also thinking about possibility of swapping out the carbs. Mabey convert to 2x keihins or something. Any thoughts?

 

Does this bike have Hatachi carbs or are they Mikuni's

 

I just checked those are Mikuni carbs which are notorious for the seat orings for shrinking and leaking fuel around them causing flooding issues. You need to check the float levels with the weight equal to the amount of fuel in the tank. Enough pressure and those seat orings will leak if they are the wrong ones or old and shrunk up.

 

Have you ever tried to set the mixture screws to 2.5 turns out as previously suggested ? Lean mixture may foul the spark plugs too, then they are black, but dry black instead of wet black when mixture is too rich.

 

These are hitachi hsc32's

Ive tried 2.5 turns out with the mixture screw.

I am getting dry black carbon deposits on the plugs, but number one is still way overfueling i believe.

Ill play some more when i get a chance and ket uou know how i go...