XJ 550 Mikuni carb problem.. Help

Just the facts. 1 Carbs are spotless, inside and out
2 New Float needles and seats
3 New float bowel gaskets
4 Passages are clean and clear
5 The bank of Carbs is off the bike and level when
attempting to set the float/fuel levels
6 I've read everything on this site about carbs. and have learned a lot.
7 The float looks fine, and moves freely like the other three
The bike is ready for the road except for this one problem, after sitting for most of it's life.( 9,000 original KM)
THE PROBLEM:
#1 carb continually overfills with gasoline when I try and set the static fuel levels. The other three carbs are fine. I removed the needle and seat and examined every nook and cranny. everything looks good. the taper in the seat looks perfect. I exchanged the needle with another carb. No change, still overfills and runs out #1. Is there another possible source of this problem besides the needle /seat/float assembly? I will try exchanging the complete seat/needle assembly with another carb. What else can I try ? 8O I must have had the float bowels off at least a dozen times trying to solve this problem, maybe thats why the bike was parked after the original owner got fed up trying to get it to run right ! I'm stumped, but I won't give up! What have I missed ?

I've been working on this bike for two years now and this is the last hurtle
before a road test. Any comments would be appreciated.

 

The Mikuni float valve seats are sealed into the carb body via an o-ring. If the o-ring is damaged or shrunken, etc. then that bowl will flood even though the needle and seat itself are fine..........

 

The o-ring is there and looks fine. arragh!!! :roll:

 

Maybe the float is bad. Swap another one into that carb and see if the problem follows.

MN

 

I will put that on the list.

 

Incorrect Float Height
Bad O-Ring Seal
Float Valve Body "Cylinder" tarnished; needs refinishing
(Roll a tight cigarette of 1500 - 2000 Grit Finishing Paper and refinish Seat

Float Pin Geometry.
The Float Pin's retaining wire is lifting the Pin at an angle and it gets stuck.

Bad Float (if Brass)
Replace the Whole Float Valve Body and Pin.

O-rings available super cheap at Home Depot.
Cheap enough to buy two blister packs to make sure you get the right size.

 

I'm voting "float pin geometry" or possibly a bad float?

 

How about you pull all the bowls and hook up some tubing to the fuel supply T and blow into it while you hold the carbs as they would be mounted on the bike...

With the floats hanging down free, all four carbs should pass air past the needle, but you should be able to masking tape all the floats into the "up" position and they should all seal their respective needle valves.

If they all seal when held by hand or with tape, then I'm with MN-Maxims... Maybe the name "float" is a misnomer!

Burnarr

 

I wouldn't bother trying to do a leak-detection test relying on Hand or Taped-up Floats.

The thing to do is to buy New Float Valve Body's and Pins.
Done.

 

Hold the rack upside down with the floats and valves installed. Bowl off #1.

Dribble a little soapy water liberally around the float valve. Blow in the fuel line. See just where it's leaking by the bubbles.

 

Call me an engineer, but how about first determining that's where the real root cause fault truly is? I mean, what happens if he holds the floats up on all four carbs and for some reason it still passes air? I'm not saying that's what's gonna happen, but hey... What if? :?:

 

Hey, I'm all about testing.
But, it's a leaking float.

I would expect a call from Engineering wanting to know how many Amps are going to be pulled when another Member hooks-up some auxiliary lights!!!

These XJ Alternator-Rectifier set-ups are running off two little Carbon Brushes. Not an array of Control Rods keeping a Pile of Nuclear Reactive Material from reaching Critical Mass.

 

Haha! Yeah, what can I say? I'm an engineer to the core. Nothing I can do about it... It's a way of life. :lol:

I've not got involved in any of the electrical discussions yet. I'm assuming I'll eventually end up with the same problems with my bike as everyone else sooner or later, but for this week, it's just carbs.

 

have you tried bending the tab more so that it seals the pin at a lower fuel level in the bowel? I have adjusted the tabs quite a bit without seeing much change in the fuel level and it has cured the fuel overflowing.... at least you can eliminate the other possible leak points

 

WOW !! Thanks for all the feedback. I will try these suggestions, and start a new thread if/when I solve the problem. Then I will post some pictures. She looks pretty good for an antique. I powder coated the frame a silver metalic