Wet setting carbs, having problems... :(

By all accounts, the tang level I have set is the same across all floats.

Test 1 - ensured the carbs were level based off a spirit level across all 4 carb hats, and level straight on from carb 4.

Carb 1: 1cm low
Carb 2: Perfect
Carb 3: 2cm low
Carb 4: Almost no fuel - literally a drop.

I drained the carbs, flipped the rack over and checked the tangs (made no adjustments). To check the fuel rails and flow - I shot compressed air through the fuel line - and all of the floats started to, well...float on air.

When the floats were off, and being rechecked - I checked all the needles, and they were all springy and working. Everything but the floats are new from Chacal.


I got everything buttoned back up, and ready to retest. Again, carb 4 did the same no fuel bit. I tilted the rack side to side, I was even able to shoot compressed air back through the carb and see air flowing up the fuel line! But no fuel would flow into the carb.

When I rebuilt them a few weeks ago, I got new seals, and made sure to spread silicone grease on the o-ring fittings too.



With all of that said, my 2 issues are these -- why isn't carb 4 getting fuel; and why would the fuel levels all be different if the floats are set identical?

Thoughts, comments, exorcisms welcome...

 

spring tension of the needle valve might have something to do with the fuel levels not being even across the board.

 

stuck needle in #4 causing no fuel in bowl maybe........

 

All new. For the sake of testing if they're stuck -- I took out the floats, and shot compressed air through the fuel line -- and all the needles shot out of the seats onto the table.

New idea -- pyrex carbs. So we can see everything inside of them!

 

did you buy aftermarket float needles......which are about 1mm longer than the OEM needles....float adjustment is necessary for which you did......something is causing no fuel in Carb #4.....if carbs are on bike.....take the float bowl off if you can......& turn the petcock to prime.....to see if fuel is flowing to #4......

 

Even if the needles were different heights -- they'd still be open if no fuel was in the bowl.

You mention a good idea - and I'll try it - removing the float and needle.

With the carbs off the bike, I've only been setting it to prime too.

 

Get a pyrex measuring cup. Use it instead of the float bowl on #4. See what happens. The needle may be sticking. The float may be getting hung up on something and not be able to drop enough to lower the needle. There may be a bit of "crap" stuck in the fuel inlet passage of #4 that can be blown back toward the tank, but not find it's way past the needle seat, which would block fuel flow (acting like a check valve).

 

Well, I managed to get it working the next day. Chalk it up to voodoo.

I pulled off #4 carb from the rack, checked all of the passageways, and fuel seat. Proceeded to put it all back together and on the subsequent test - #4 filled the bowl!


I'm still having problems getting the float levels just right, but I suppose once they're done now, they'll be good for another 30 years.

 

Wet setting fuel levels in on my top 10 list of things I hate to do the most... it's a 12-pack job... 1 nano-millimeter of tang adjustment equals about 2mm of fuel level change.

 

So, carbs are rebuilt and wet set - put back into the bike, but now it only starts with starting fluid.

Battery is charged, I've tried choke on and off, and even kept the throttle at WOT and it wont stay running.

After initially rebuilding the carbs, I set the mix screws to 1.5 turns, but proceeded to change it to 3 full turns from the bottom.


Regarding the carbs, the enrichment circuits were cleaned, zestfully (!), the bowl jet was cleaned up, and everything was poured over to be as clean as possible.

I'm at a bit of a loss now. Hopefully more searching the forums will reveal something...

 

Just to be 100% sure...

In your initial post you indicate the fuel levels were low by cm (centimeters)... you did mean mm (millimeters).. yeah?

 

Nope, I meant centimeters. It's possible the carbs weren't entirely level, but the big difference was when I was playing with the tang on one of the carbs - not realizing... I think someone put it best -- nanometers equate to a few mm. So I bent it back inline with the other floats, and then proceeded to fine tune it.



Present issues is that the bike wont start without starter spray. Everything is much cleaner than it was -- so I'd imagine it should fire right up, but alas it shares its fate with poor Yorrick, for now.

 

I should add before I get reprimanded by Fitz, HogFiddles, or Rick -- the valve clearances have been checked and brought into spec about 50 miles ago (last fall).

 

Did you:
A. Bench sync the butterflies? If so, what did you use for a gauge?
B. Try adjusting the idle knob?

Also, when is the last time you changed the plugs? And what do they look like?

WOT doesn't enrichen the mixture like the enrichment circuit does because you are letting in more air along with the fuel, it just floods the carbs.

And, is she breathing ok? (i.e., clean air filter)

 

when i replaced my needles + seats, i had to bend the tangs way down and kinda start over. believe it or not, the 1 mm makes a huge difference in your carb set up

 

Did you ever get the bike to start up?

 

My bike was running lean so I adjusted the floats so the fuel level is 2mm deeper and now it won't idle or start without starting fluid. Wow, these carbs are sensitive ! I'll set the floats back where they were.

 

How about setting them TO SPEC: http://www.xj4ever.com/setting%20fuel%20levels.pdf Then they'll work properly, as long as the seats are clean and the float needles in good shape.

Read the 'pdf' carefully; you are adjusting Mikuni BS28's. (A lot of the illustrations are Hitachis.)

Float levels in the Mikunis are very important and will greatly affect how the bike runs. The spec (2mm below mixing body edge) only has a +/- 1 mm tolerance; these carbs reward precision.

Here's an exploded Mikuni for reference: http://xjbikes.com/Forums/viewtopic/t=31061.html

You didn't answer my valve shim question in your other thread.

 

literally, when doing wet-setting, if you can see that you moved the tang, you moved it too much. bending the tang about 5 mm or so will take the bowl from empty to flooding.

As was stated before, it's a 12 pack job. and time and patience. but you gotta do it, and gotta do it right....

 

You do. Which is why it's more of a "Sunday morning with a cup of coffee and a clear mind" job; and save the 12-pack until after. Kinda like doing valve clearances.