Jet type for 1978 XS1100

[WMarshy]

plug coloring is currently a perfect light tan color. If I change and put air filters on it the plugs are much darker to fouled black depending on how close to stock I get on the air filter...

...as to ignition problems, since it runs perfectly as is with no filters, I don't forsee an ignition problem. has to be a jetting issue.

Verify what carbs you have using this link.

You have to know which type carbs you have.... look here:
http://www.xs11.com/forum/showthread.php?t=35964

Then I would recommend you buy some new stock size Mikuni jets, proper size for earlier (137.5) or later (110.0) carbs. Maybe someone drilled out the jets you have installed.

BTW, it appears he has the earlier style carbs b/c I can see the idle mix screws in his picture...I think.

[brharris27370]

Definitely looks like 3 air holes to me and screw in front is definitely exposed.

[brharris27370]

also measured my primary header tubes and they are 38mm or 1.5 inches outside diameter. Don't know what stock was. Just hate to buy the same size jets I have and possibly the exact same issues but I have had the drilled mains before but bike just look too stock for someone to have gone and done something like that.

[natemoen]

You have some other carb problem. The exhaust is not the problem, plenty of people have aftermarket exhausts on their bike and they have the full 1.5 " pipes. The stock pipes reduce down on the inside in diameter. Did you ever look at your air filter(s) to see how well they flow?

Yes you have the early style carbs it appears, so that means you need to be up in the 137.5 jet size range. Going lower in jet size is not the solution, all it would do is maybe mask the real problem and probably end up biting you in the the butt later on! You need to take the carbs off and figure out what the problem is, jut change here IS NOT the answer.

[brharris27370]

so if I want to try a set of new 137's, I need the large round jets?

http://www.ebay.com/itm/Mikuni-Large-Round-Main-Jets-137-5-N100-604-137-5-/310456201145?pt=Motorcycles_Parts_Accessories&hash=item4848a1afb9&vxp=mtr

[natemoen]

Yes, 4 large round jets, genuine mikuni only. Although get away from that eBay seller! Those jets only cost a couple dollars. Go to a local dealership and check their price or go to jets r us website.

[motoman]

so if I want to try a set of new 137's, I need the large round jets?
http://www.ebay.com/itm/Mikuni-Large...a1afb9&vxp=mtr

Those are NOT Genuine Mikuni!.........key word, always.....GENUINE! GENUINE! GENUINE! Lots of copy-cats out there(K&L, RD being major aftermarket makers.) Even tho numbered accordingly, not the same hole sizing.......not even close! Goes for ALL the related jets in Mikuni carbs! Genuine Mikunis have the curly looped line marked into them, tho on the pilot jets I need a magnifiing glass to see, but it will be there if Genuine, on ALL their jets.

[DGXSER]

You definitely want to shop pricing on those jets a little bit. I just ordered new pilot jets for my GSX today. One source had them listed at about $8 a jet, I got a set of four for $17.

Not to rant over Moto's rant, but, while you certainly can not go wrong getting the genuine Mikuni parts, I have installed K&L Kit jets in most of my carb banks and never had a problem getting the carbs to tune or run well.

[brharris27370]

I believe I will have to take motomans advice on this one. I don't want to cause yet a different issue by cheaping out on those parts so I will put true mikuni jets in the thing. That way I KNOW its right and then go from there figuring the thing out if it still has issues.

[WMarshy]

I think your float height might be off. Did you mechanic set the floats when he was in the carbs? IMO you need to take them off the bike and check the height. You can do this yourself with very little effort because the air box it off. Just need a machinist scale or a pair of dial calipers.

Drain and remove the bowls, flip the carbs upside down and set them on the bench. Take the gasket off the carb body and measure from the carb body gasket face to the highest point on the float. They should be ~23mm IIRC, maybe someone will chime in the the exact height. Stock floats are brass, if you have plastic floats the height is slightly different.

Let us know what floats you have and what you measure them at. You jets might be just fine but if the floats are off then they could cause a rich condition. Thats about all I can think of, check the easy things first like float height before you go changing jets.

Dont worry if your not good with carbs/tunning, you will be when we are done with you.

Float height Tech tip:

http://www.xs11.com/forum/showthread.php?t=76

[DGXSER]

Float height for the early style carbs is 25.7 mm +/- .5 mm. 23 MM is for the later style.

[brharris27370]

I have had float issues on bikes before and that typically causes more problems with the light throttle rather than heavy throttle unless the level is too low and then its not instant problem but usually several seconds into full throttle. this one is VERY instant, with full filtration as soon as you start getting into the mains at 1/4 throttle or so it starts misfiring by 1/2 throttle you can't see behind the thing for the black smoke.

[WMarshy]

We can give you suggestions all day but if your not willing to validate them we'll just continue to guess.

Float height is the only thing I can think of that would explain why you are so rich with stock jetting and free flowing intake and exhaust.

[brharris27370]

well I personally HATE pulling carbs off these things and doing multiple times does not appeal to me. While I am changing the jets, I have a caliper that I an measure the float level just like I measured the header primary tubes earlier. I know my mechanic checks those things as he has commented on some of the junk I have taken to him before having the levels out of whack.

[motoman]

well I personally HATE pulling carbs off these things and doing multiple times does not appeal to me. While I am changing the jets, I have a caliper that I an measure the float level just like I measured the header primary tubes earlier. I know my mechanic checks those things as he has commented on some of the junk I have taken to him before having the levels out of whack.

Well, least you'll get good at it. Their IS a trick to it, and can have them on the bench in bout 12min. Pull seat and tank(included in the time), remove crankcase vent hose(goin back it goes either direction), remove lower portion of air-box and filter out left side, remove the two side bolts and top bolt holding upper portion of air box, loosen the four airbox boot clamps enough to slide them up against the air box, rock the upper air box off carbs, pull back and down letting front portion of air box rst on engine case. Rotate full throttle, then holding linkage full open, rotate throttle back off and jiggle throttle end out of linkage holder. Loosen carb to engine boot clamps, rock carb bank off of boots and remove out left side. Actually, these are the easiest multi- carb bank set up to remove, compared to a V motor like an ST or even worse, any of the VFR series with Kiehn downdraft carbs.