I think these carbs are having an ignition problem ....

[Barbarosa]

Non runner that sat appx 2 yr. Cleaned carbs etc to get it to start. 1980 SG would start and idle. Carbon fouled all the plugs in short order. Static set the floats at 23mm with KL valves. Bench tested levels are #1 and #2 middle of bowl lip. #3 bottom of lip, #4 top of lip. Where should the fuel level be for these carbs to function properly? I have seen several different answers and am still unclear where the sweet spot is. I have pics of my testing if that would help explain where I'm at.

[motoman]

K&L float needles can create an actual fuel level issue. On your 80 model, fuel levels NEED to be at middle of screws lock washer....period. Any more or less WILL create running issues, and even a half a millimeter to high a fuel level WILL cause to rich a condition and cause blackened plugs. This is VERY critical for the 80-XJ series having the later model Mikuni carbs. In fact, the fuel levels on the 81-XJ series HAVE to be checked with motor running, and at an idle. This IS specificly stated in the 81-XJ Yamaha SHOP service manual!

[Barbarosa]

KL seems to have a bad rep on the xs around here. Looks like I have 3 way off and 1 almost there. Anyway, half a washer thickness below the bowl lip it is. Thanks for the quick reply and I will post back with results

[dbbrian]

K&L have bad rep elsewhere too - like the SOHC4.com forum for Hondas. The parts don't match OEM and cause people trouble with their carbs.

[motoman]

KL seems to have a bad rep on the xs around here. Looks like I have 3 way off and 1 almost there. Anyway, half a washer thickness below the bowl lip it is. Thanks for the quick reply and I will post back with results

Must of mis-read my reply........fuel level is to be at half way of the lock washer that is used under the float bowl hold down screw. In other words, fuel level is to be at 3mm which is measured from top of float bowl casting itself.

[Barbarosa]

Must have been blind luck but got all 4 levels even with the top of the washer/bottom of the lip on the first try. Could not believe how even they came out. Started right up and held a good idle. Warmed up it fires off with the slightest touch of the starter button. Idle hangs at 3k for a spell, hopefully due to out of synch condition. In the process of building a tool for that. Plugs still show as sooty, but MUCH better than before. Anyway, it's running on the aux tank from my float setting rig. Maybe that half a mm that was mentioned before is still an issue, but I will put the tank on tomorrow and see how it does under a load before I have another go at the float levels. Getting the tubing to seal in the drain holes is a PITA lol. Looks like it's going in the right direction though, thanks for the advice

[motoman]

Must have been blind luck but got all 4 levels even with the top of the washer/bottom of the lip on the first try. Could not believe how even they came out. Started right up and held a good idle. Warmed up it fires off with the slightest touch of the starter button. Idle hangs at 3k for a spell, hopefully due to out of synch condition. In the process of building a tool for that. Plugs still show as sooty, but MUCH better than before. Anyway, it's running on the aux tank from my float setting rig. Maybe that half a mm that was mentioned before is still an issue, but I will put the tank on tomorrow and see how it does under a load before I have another go at the float levels. Getting the tubing to seal in the drain holes is a PITA lol. Looks like it's going in the right direction though, thanks for the advice

Yup.......still a bit high(dang K&L parts) fuel level needs to be at center of lock washer. Do that, set idle mixtures(lean-drop method) and THEN sync, go ride with the permanent grin.

[Barbarosa]

Didn't record the static settings after adjusting, but they are all over the place. None are at 23mm now and one was 25.5mm. I estimated what needed to be made up from the initial settings when I started bending tangs. That's why I freaked when they came out so even on the bench test.

[motoman]

Didn't record the static settings after adjusting, but they are all over the place. None are at 23mm now and one was 25.5mm. I estimated what needed to be made up from the initial settings when I started bending tangs. That's why I freaked when they came out so even on the bench test.

Just a bench test of settings kinda works. Problem with that, is in order for fuel to totally shut off, fuel levels end up a bit high cause in order for float needles to totally pinch off fuel flow, a bit more pressure is needed. That bit more pressure also pushes up against that teeny spring in the float needles, slightly raising that fuel level. In my opinion, if one is gonna do an 'on the bench' static fuel level check, that fuel level ought to be 4mm or at least 3.5mm instead of 3mm down from float bowl top edge.
With the 81's and XJ's specifying 3mm fuel level setting done with motor idleing, and them having the drain nipple and nipple fuel shut-off screw on side of fuel bowl to be done while idleing keeps the above mentioned from taking place. I also realize that gets you really good at carb removal and installation, since you'll be doing that several times to get all four fuel levels identical. Identical fuel levels also has all four cyls. doing the same amount of 'work', which is really important also.

[motoman]

Also, the 78-79 Mikuni carbs are a bit more forgiving having the cross-over fuel passage, where the 80-XJ carbs eliminated that to better meet the emission standards in order to be exported here from factory. I know, makes the 80-XJ carbs a bit more finiky to run perfectly, but it is what it is.

[motoman]

For a bit of encouragement, I guarantee if all floats are set identical, no two carbs will have the same fuel level......have to pull carbs and adjust float levels just a tad to get them all identical fuel levels.

[Barbarosa]

Was thinking to shoot for the bottom of the washer next go around. I read about the "running level" test and can't see any way to do that on this bike. It's hard enough sealing off the tubing for bench testing; I can't imagine trying to manipulate the lines without them being pulled loose and soaking down the motor with fuel. Makes me wish I had a lathe. Could center drill a drain bolt and epoxy a nipple on it to attach the tubing. Or maybe someone has already made something similar and I just haven't seen it.

[motoman]

I might add, since 81's and XJ's are required by the ORIGINAL Yamaha shop manual for fuel levels to be checked while engine is idleing, one gets really good at removal and installation of carb bank/air filter installation. Including seat and tank removal along with carb removal, I got it down to 12min. including carbs upside down and float bowl removal. Now, XJ air filter box removal.....not near as easy to remove and install.....a bit of a PITA.

[Barbarosa]

After this I will never complain about my Super E again. They are supposed to be simple. Was only able to get it to run perfect (well as perfect as a dinosaur can) by cutting 1 1/2" from the aft exhaust pipe. You don't want to know how long it took to figure that one out,

[mack]

Idle mix screws

make sure your mixture screws are all three turns out to start. Then adjust them as required until you get the proper colour of plug in each cylinder. Again they might all have different adjustments. The other thing to check is that the small rubber washer at the tip is in good shape.
Just as a side note, I always have a set of syncing plugs. To get the sync and mixture settings correct it can take some time. The idling will foul the plugs pretty quickly until you get them right. Then I pull those ones out and put in a clean set and run the bike hard while riding in all rpm ranges and make finer adjustments to the mixture screws until I get the colour dead on, then one more quick sync and your don't have to touch them again for quit some time.
Make sure you have a large box fan set up and running while the bike is being tuned. These are air cooled and can get pretty hot real fast.