1. Dismiss Notice
  2. Hey Facebook people... We've created a group for XS650.com members to connect. Check it out!
    Dismiss Notice

What size jets for my new xs650f?

Discussion in 'The Garage' started by cafetools, Feb 11, 2019 at 12:08 PM.

  1. cafetools

    cafetools XS650 Addict

    116
    90
    28
    Utah
    1978, 17k miles, original motor is healthy, good compression. I cleaned the carbs, had to buy new brass floats (China). I got a carb rebuild kit with a new bowl gasket, new float spring pins.

    I am running UNI filters with red prefilters (oil sticky sprayed) and using Norton commando mufflers. These pipes are loud, you can see straight through them. I think it sounds good though!

    I am using iridium NGK's, and fuel filters. 91 octane premium gas, and a electrosport solid state reg rec.

    So with aftermarket intake and exhaust maybe I am getting a little more backfiring than desired. Maybe less power. If I were to go on eBay (or other site) and buy some jets what should I buy?
     

    Attached Files:

  2. timbeck

    timbeck XS650 Junkie XS650.com Supporter

  3. 5twins

    5twins XS650 Guru Top Contributor

    16,559
    5,367
    688
    With a stock '78-'79 carb set (make sure they are those carbs), the usual routine for mods like yours (the typical pods and pipes) is 1 or 2 up on the pilots and 2 or 3 up on the mains, AND you must lean the needle setting one step with the larger mains. Stock jet sizes for the '78-'79 carbs were a 27.5 pilot and a 135 main. That means you'll want #30 pilots and 140 mains to start. Eventually you could try 32.5 pilots if you feel the idle circuit isn't quite right, and 142.5 mains if you feel it needs it.

    I prefer to use genuine Mikuni jets. They con't cost much, if any, more than the knock-offs and you can be assured of the quality and that they will flow correctly. A carb jet is a precision part. Many have been getting their jets lately from Niche Cycle .....

    http://www.nichecycle.com/ncs/categories/carburetor/mikuni-parts-by-category/jettting-tuning.html

    You will want the N102.221 main jets (called a "small round main") and the VM22/210 pilot jets.
     
    lakeview likes this.
  4. cafetools

    cafetools XS650 Addict

    116
    90
    28
    Utah
    It's a 79f standard. Not a special.
     
  5. cafetools

    cafetools XS650 Addict

    116
    90
    28
    Utah
    5twins, thanks for the invaluable wealth of knowledge you shared. Hopefully it will run a little better!
     
  6. timbeck

    timbeck XS650 Junkie XS650.com Supporter

    Follow 5T's advice. I run 140 mains and 32.5 pilots.with UNI's and modified exhaust and it works good for me.
    tim
     
  7. XSLeo

    XSLeo XS650 Guru

    When you bought the carb kits, did it come with any internal parts? More than just gaskets. If it did they probably are not the right ones.
    Mikuni built carbs similar to these that fit many bikes. Most carb kits come with generic internal parts. These parts may work one something, just not our XS650's.
    If you have read the carb guide, you know the routine for tear down, cleaning, inspection. You need to do this so you know just what to buy. If stock parts are good, no need to replace. Often if careful you can reuse gaskets.
    Ok, We can assume you did a good job of cleaning. The stock jets in a 78/79 carb set were 135 mains with 27.5 pilots.
    So as 5twin's recommends get a set of 137.5 and 140 mains, 30 and 32.5 pilots.
    I, as others would rather see you use genuine Mikuni parts, better quality and about the same price as Chinese knockoff's.
    If you haven't read the carb guide you can find it in the TECH section.
    I just can't recall the link hook you up.
    Leo
     
  8. 5twins

    5twins XS650 Guru Top Contributor

    16,559
    5,367
    688
    Honestly, I think you can skip right over the one size larger main (137.5) and go right to a 140. If you wanted to get an assortment of sizes, I'd recommend the 142.5 over the 137.5. You might need and use that, but I doubt you ever would use the 137.5. Sure, maybe for testing, for a short period of time, but that would just show you it's too small and you'd be changing it up to the 140.
     
  9. cafetools

    cafetools XS650 Addict

    116
    90
    28
    Utah
    Ordered genuine 30s and 140s from niche. Also a gas cap with keys for $20 (which I need badly) hopfully quality is decent.
     

Share This Page