carburetors

[motorman]

I am having a problem getting my fuel mix leaned out properly. This is my first experience with a 4 carb set-up, but I didn't expect this much trouble. I am working on a '79 XS 1100 SF, and am only able to get about 15 - 20 miles before the plugs are so carbon fouled that it will barely run under 4000 rpm's. Is there an optimum FUEL level setting that would help to alleviate this over rich situation? My fuel level is currently at the bottom of the flange on the float bowl, equal, +/- .015", with the seat of the float bowl retaining screws. All 4 carbs are set the same as measured with a clear tube screwed into the drain hole. The needle in the slide is set in the 4th groove from the bottom. Everything inside the carbs is new with the exception of the floats, these are still the oem brass units. All air bleeds and feed holes appear to be clean and open when shot with carb cleaner.
I do have a set of aftermarket individual air filters on the engine, and the factory 4 into 2 exhaust system with low restriction aftermarket mufflers. When a clean set of spark plugs is installed, this machine is a real powerhouse, but it gets to be real pain-in-the-butt to have to stop every 25 miles and change plugs. Can anyone help me with this situation?

[TopCatGr58]

Hey there Motorman and welcome!!

Okay, you've given us "some" info, but what size are your main and pilot jets. You say that everything inside is new....this may mean that you recently got a set of carb rebuild kits, and depending upon where you got them, quite a few of them are notorious for putting the wrong sized jets, both main and pilot in them, causing them to run exceedingly rich!! Stock mains should be 137.5 and Pilot 42.5. Also if you're not the original owner, the P.O. might have already put in larger jets for the Indy Filters and modified exhaust!?

You also state your slide needle is on the 4th notch from the bottom, if you mean bottom as closest to the needle point, then you've gone the wrong direction, you want it in a notch further away from the needle point, so that the needle protrudes further out from the slide.

Also, the technique you're using for your float height is for the later model carbs circa 81, for your earlier model, you should try getting the measurements from the bottom of the float to the edge of the carb body when they are positioned upside down, which should be around 25mm, and if yours is shorter=richer than that, then you'll need to adjust to attain that.

You also didn't mention about your pilot idle screws adjustment, those on top of carb next to intake mounting flange, they should be about 1 1/4 turns out from "GENTLE" seat to start with.

Finally, what RPM range do you run the bike in, since you mention running below 4K, that's barely INTO the power range of this engine, you need to be revving it up to 6 or 7 and then try to keep it above 3k in whatever gear you are running in!

Hope this helps get you started in the right direction. T.C.

[Winterhawk]

Mine had a K&L Carb Kit in it and the Pilot Jets that comes with it are not the right size. Use Yamaha pilot jets and it will run fine. Braden at Merriam Cycle found this problem for me right off the bat. Runs great now. That parts bike on E-Bay that I got last week is on the road and running great thanks to Bob Jones and crew.

[motorman]

OK, thanks for some response. The main jet is a 137.5. The pilot jet is 42.5, the air adjuster is at 1 1/2 turns out, and the needle IS at one groove toward lean, making the effective length of the needle longer than if it were in the center of the 5 available grooves. Yes, I did install rebuild kits from K&L mfg. I have noticed that I am able to force fuel thru the new needle and seat valves when the carbs are upside down and clamped to my bench, by blowing thru the fuel feed line with my mouth (93 octain tastes awful). Could these valves be leaking at low rpm and causeing the rich condition? There is NO fuel spillage either from the carburetor vent tube or from the air cleaner end of the carb if the machine is left setting with the tank valve in the prime position. The method you described to set the floats was used, and resulted in fuel levels that I described. Since I don't have metric measuring tools, my measurements are in inches. Float heights currently are set at 1.060" to 1.080 inches, measured from the bottom of the float to the gasket face of the carb body, without the gasket. This results in the fuel level described in my last question. Will get this figured out soon I hope, the rain is supposed to stop here in N.E. Ohio pretty soon, and I need to get this thing on the road. Thanks, Steve.

[Winterhawk]

K+L float needles and seats will not seat as well as OEM. If you used K+L's pilot jets they are not stamped and are larger than 42.5.

[pathfinder]

Floats are to high

1.060" to 1.080 inches = 26,92mm to 27,43mm. Should be 25mm =.980
25.4mm = 1"
To convert Inch to millimeter, multiply inch by 25.4
To convert millimeter to inch multiply by .03937 or devide by 25.4
Your floats are .080 - .100 high. Reset you floats to .098" and your problem should go away.

[motorman]

The 1.060" measurement that I used is with the carb upside down and measured as described in the Clymer service manual. If floats are set at the .098" level, I get trickles of fuel running out of the overflow/vent tubes. Been there - done that. Steve

[TopCatGr58]

Hey there Steve,

Yeah, I saw that you already had your floats set pretty high/lean! As Winterhawk stated, sounds like your new float needles/seats, but also your new jets may be suspect. Just cause the K&L package says they are a certain size, folks have reported that they aren't, wrong # of holes in sides of Pilot jets, the mains much bigger than the same size OEM, etc.! If you have your OEM jets, you might try putting them back in!? They don't necessarily wear out, just get dirty, so after a good soaking and brushing with toothbrush and such, they should be quite clean and reusable!!

The OEM brass floats....did you check them for leaks, putting them in warm/hot water and submerging and checking for air bubbles? Are the new float needles rubber tipped or solid metal? If solid, someone suggested a small drill bit that will fit into the valve seat, turned backwards to help clean up the seat?

Another Xsive with leaky carbs posted about the ports in the air filter chamber where the carb vent tubes attach were clogged, vents couldn't breath, have you checked your vent lines and where they attach for cloggs? Just trying to come up with other things that might contribute to check!? Good luck!
T.C.

[motorman]

I have had several people tell me about the suspect K&L pilot jets. I still have the old ones and will check that out very closely this week end. Since I am using aftermarket individual air filters, the carb bowl vent lines are just hanging down between the carbs and are no longer connected to the air box. They are not plugged. I will also check the floats in hot water this week end. I will also be driving to Knoxville Tenn. this week end to pick up another engine/transmission assembly with only 8004 original miles. Thanks for all of your input, it looks like the pilot jets may be the most likely suspects in this mystery. I will advise what I find out. I did locate new floats if these proove to be defective beyond repair, At Speed & Sport in Pennsylvania. $22.00 @. Steve.

[sidecarKev]

If you need to you can get floats from www.mikesxs.com he has them for $10 each including shipping. For some reason he doesn't have them on his website but they are in his catalog. They will be plastic instead of the brass ones you have in your '79. If you do order them make sure you get the plastic ones for a 34mm carb. They will be more kidney shaped rather than round but they work just fine. Set the float height the same way.

[motorman]

Thanks for the heads up on the floats, anything to save a buck. Steve

[motorman]

OK guys, here's the skinny on what happened today. I pulled the old pilot jets out of the old parts box and compared them with the new jets from the K&L kits. I was amazed!!!! The K&L jets were nearly half again as large as the original Mikuni units. I changed them out and reset the floats to a more reasonable height. The results were truly amazing, although I suspect that now I am a little lean since I did not reset the clips on the needles. Throttle response is good, and the plugs now are very clean, nearly white, after about 50 miles of riding, another sign that I may be a little too lean. Thanks to everyone who offered council in this situation, and boo-hiss to K&L. I would have been pulling my hair out trying to solve this with out you-all. Thanks again, Steve.

[Winterhawk]

Congratulation Steve, I hope you fixed it. K+L makes good fork seals but the petcock kits are not right. Braden at Merriam Cycle gives me all my trick info on XS1100's. I have my E-Bay (two Rivers, WI) bike on the rode now and am painting and polishing it. I'm in XS ELEVEN HEAVEN now for sure. Larry