XS 11 Jetting question

[shawn01505]

I just bought a 79 xs eleven with an after market 4 into 1 exhaust. I ahve the bike starting and running well but up over 5500 rpm's I sputters and will die if you don't let off the throttle. I need to know what main jet size I should be running. I have the stock air box and ileter in place. Any help would be great.

[John]

It should have 137.5 main jets in it if it hasn't been messed with. That is stock. I would try the next size up, That would be 140's. Is the filter clean? How about the inlet snorkel? Any blockage?

[thumperjsa]

I had a problem similiar to what you are reporting. Check the height of your floats in the carb and make sure you have no leaks on the intakes too.

[shawn01505]

XS 11 Jetting

I actually just figuredout the problem. As it turns out I got the bike with 155 main jets. I put in the 137.5 jets that the manual says I should have. I also tried every needle and fuel screw setting possible. I finally sadi screw it and went with 117.5 mains just to see what would happen and waalah. I am not yet 100% sure that this is the final main jet I will use but I now know I am close to where I need to be. It is just amazing to me taht I had togoo muchsmaller than the manual said. I am thinking that maybe I don't havethe stock carbs. What the hell it runs really well and strong so I'm happy!! Thanks for the reply!!.

[TopCatGr58]

Hey Shawn,

IF your carbs DON'T have the extra set of "T"s above the float bowl level, just the one set down at the float bowl level, then you DO have later year carbs....circa 80-81. And they only use smaller mains like 110 to 120 with stock pipes/intake box. The pilot circuit gets it's fuel directly from the bowl, vs. the 78-79 that get it from the main jet circuit.

So...your 117.5's may be just about right? However, if you DO have the extra Bowl Vent "T's" and the earlier year carbs, then you may NOT have the pilot jet caps in place, and therefore running the pilot circuit too rich due to pulling fuel directly from the bowl instead of thru the main jet tube!?

And....your PO may have used K&L type jets from a kit, and they are notorious for being labelled wrong due to different sizing scale vs. Mikuni!
T.C.

[shawn01505]

XS 11 Jetting

I will look for the T's in the morning. I have to believe that the 117.5's are correct size because the 137.5's and the 155's didn't help. I did put the pilot jet caps on but thanks for the tip, I did not know that about them.

[TopCatGr58]

Hey Shawn,

If they are the later model carbs 80-81, then you DON'T want to use the pilot jet caps! Only if your carbs are the earlier ones would you want the pilot jet caps on! And if that's the case, then the 117.5's will probably be too lean!? You may have other problems, like pinholes in your vacuum slide diaphragms, the Slide needles may be too far UP, also to rich? Also, floats may be set too low....also too rich?

Are you sure your 137.5's were Mikuni jets, and not K&L aftermarkets? IF your carbs are early model ones, then you'd want to go back with these jets, and check the other settings!
Good Luck! T.C.