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  • #1

    Carb jet conversion

    I'm about to rejet my carbs to accomodate 4/1, freeflow airfilter, and drilled airbox. I noticed in another thread that TADracer said "aftermarket jets might flow differently than Mikuni jets".

    As I was checking prices I found this jet conversion table covering mikuni, dynojet, and keihin on the Jets-R-Us website. Evidently the numbers on the jets mean different things, depending on the manufacturer. Very illuminating. Hope this is helpful to some of you struggling with dynojets.

    http://www.jetsrus.com/FAQ_mikuni_vs...ihin_sizes.htm
    I think I have a loose screw behind the handlebars.

    '79 XS11 Standard, Jardine 4/1, Dyna DC1-1 Coils, 145 mains, 45 pilots, plastic floats - 25.7mm, XV920 fuel valves, inline fuel filters, speed bleeders, Mikes XS pods, spade-type fuse block, fork brace, progressive fork springs/shocks, manual petcocks, 750 FD, Venture cam chain tensioner, SS brake lines
    Tags: None
  • #2
    I bought a set of small drill bits and a digital micrometer that reads in tenths of a MM to take care of that problem. In Mikuni and Hitachi carbs the jet number is the same as the diameter times 100, for instance a 120 jet is 1.20MM so find the largest drill that just barely fits and measure it for the jet size. I don't know what the deal is with dynojets that are slightly off, I don't think they know how to measure over there.
    72 TS185
    77 XS750
    78 SR500
    80 XS850
    80 XS1100 Midnight Special
    81 Seca XJ750RH

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    • #3
      I thought about drilling them, but wasn't too sure about what the end result was going to be. Ended up ordering four mains and four pilots from Jets R Us. Paid a little over $3 ea. for the mains, and just under $5 for the pilots - genuine mikuni. With shipping it was $39 and some change. The big surprise was that I ordered them Friday night, and they arrived in the mail today (Monday) - standard shipping. I love it when a company runs efficiently
      I think I have a loose screw behind the handlebars.

      '79 XS11 Standard, Jardine 4/1, Dyna DC1-1 Coils, 145 mains, 45 pilots, plastic floats - 25.7mm, XV920 fuel valves, inline fuel filters, speed bleeders, Mikes XS pods, spade-type fuse block, fork brace, progressive fork springs/shocks, manual petcocks, 750 FD, Venture cam chain tensioner, SS brake lines

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      • #4
        what jets do i need?

        OK, so if i'm doing the pod filter conversion, about what size of jets do i need to be looking for? i was planning on doing the 4-1 exuast but i belive im not going that route any more, gonna keep the stock 4-2.
        1979 XS1100 SF "Black Goblin"
        -Pod Filters
        -4-1 pipe
        -larger jets for carbs
        1982 XJ1100 "Black Sheep"

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        • #5
          I'm not a guru, but the gurus say check this thread:

          http://www.xs11.com/forum/showthread...=&threadid=382
          I think I have a loose screw behind the handlebars.

          '79 XS11 Standard, Jardine 4/1, Dyna DC1-1 Coils, 145 mains, 45 pilots, plastic floats - 25.7mm, XV920 fuel valves, inline fuel filters, speed bleeders, Mikes XS pods, spade-type fuse block, fork brace, progressive fork springs/shocks, manual petcocks, 750 FD, Venture cam chain tensioner, SS brake lines

          Comment

          • #6
            so according to the guru page, since im doing the pod filter conversion i need to increase 3 je sizes and subtract one then subtract another? according to the guru link? so i just need to increase about one jet size.
            1979 XS1100 SF "Black Goblin"
            -Pod Filters
            -4-1 pipe
            -larger jets for carbs
            1982 XJ1100 "Black Sheep"

            Comment

            • #7
              That's the way I'm reading it. You might want to check with Denny Zander, as he is the one who posted the table.

              I can tell you this. I followed the table for my '79 and it's mods (three main jet sizes, one pilot jet size). Prior to rejetting I could not attain bunson blue flame with my colortune no matter how much I turned the adjusters. I put the new jets in yesterday and colortuned and synched today - bunson blue on all cylinders, and the idle is MUCH better.
              I think I have a loose screw behind the handlebars.

              '79 XS11 Standard, Jardine 4/1, Dyna DC1-1 Coils, 145 mains, 45 pilots, plastic floats - 25.7mm, XV920 fuel valves, inline fuel filters, speed bleeders, Mikes XS pods, spade-type fuse block, fork brace, progressive fork springs/shocks, manual petcocks, 750 FD, Venture cam chain tensioner, SS brake lines

              Comment

              • #8
                clue me in here, what is a colortune? or is it just running the bike strait out the heads? so whay mods did you do to your 79? mine is also a 79 but a special...i am just going to do the pod filtersnd maybe the 4-1 of the guy ever gets back to me.

                Thanks
                1979 XS1100 SF "Black Goblin"
                -Pod Filters
                -4-1 pipe
                -larger jets for carbs
                1982 XJ1100 "Black Sheep"

                Comment

                • #9
                  A colortune is a sparkplug with a clear window in the top that allows you to see into the combustion chamber while the motor is running. You can see the actual color of the flame. You adjust your carbs until the flame you see is bunson blue - the color Gunson (manufacturer of colortune) says indicates complete combustion of fuel. A whitish blue color flame indicates a lean condition while a yellow flame indicates rich. It allows you to dial in your carbs more precisely than you can by ear or feel.

                  As for the mods on mine, their all listed below.
                  I think I have a loose screw behind the handlebars.

                  '79 XS11 Standard, Jardine 4/1, Dyna DC1-1 Coils, 145 mains, 45 pilots, plastic floats - 25.7mm, XV920 fuel valves, inline fuel filters, speed bleeders, Mikes XS pods, spade-type fuse block, fork brace, progressive fork springs/shocks, manual petcocks, 750 FD, Venture cam chain tensioner, SS brake lines

                  Comment

                  • #10
                    ...A waist of money!

                    Colortune is a very poorly designed good idea. It is esentially a glass sparkplug that allows you to see the color of the combustion flame in order to set the idle mixture. The problem is that is causes misfires due to a poor design where the spark happens way up in this tube and somehow results in a setting that is WAY too rich. Others swear by it. I bought it, hated it, gave it another try, thought it was okay, then turned the mixture back to my original 3 turns out and was amazed at the performance increase on the bottom end. Save your money. I have found that my 4-1 gives me a REALLy close setting. Lean it out, and then gradually richen it after test rides until the hard decelertion exhaust popping stops. This is the setting that has yeilded the best performance for me.
                    '81 XS1100 SH

                    Melted to the ground during The Valley Fire

                    Sep. 12th 2015

                    RIP

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                    • #11
                      The thing I like about colortune is that it allows you to set each carb to optimal condition, as opposed to setting them all the the same number of turns.

                      When I examined the mixture screws I noticed that the tips are not all straight - two were very slightly bent on the end which affects how deeply they will seat when turned all the way in. This in turn affects the mixture on that carb. When I colortuned I went about two turns out on the 1 and 2 cylinders, and about 1 1/4 turns on 3 and 4. Bike runs great - lots of power and no backfiring.

                      I certainly understand that some folks don't like the colortune as the tool takes a little getting used to. I probably fall into the "swears by it" category. As the saying goes "each to his own, as the lady said when she kissed her cow"
                      Last edited by dbeardslee; 03-20-2008, 12:19 PM.
                      I think I have a loose screw behind the handlebars.

                      '79 XS11 Standard, Jardine 4/1, Dyna DC1-1 Coils, 145 mains, 45 pilots, plastic floats - 25.7mm, XV920 fuel valves, inline fuel filters, speed bleeders, Mikes XS pods, spade-type fuse block, fork brace, progressive fork springs/shocks, manual petcocks, 750 FD, Venture cam chain tensioner, SS brake lines

                      Comment

                      • #12
                        Engines are air pumps. They can only pump as much air as the most restricted element of their design will allow.

                        Opening up the intake (pod filters) while leaving the exhaust restricted (4:2) will not make for a happy air pump.

                        Unhappy air pumps are difficult to jet.

                        Don't even get me started on "pod Filters".

                        Colour Tunes are the only way to go!
                        DZ
                        Vyger, 'F'
                        "The Special", 'SF'
                        '08 FJR1300

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                        • #13
                          ok, well i have decided to go with the 4-1 exaust.

                          this should change things up a bit.
                          1979 XS1100 SF "Black Goblin"
                          -Pod Filters
                          -4-1 pipe
                          -larger jets for carbs
                          1982 XJ1100 "Black Sheep"

                          Comment

                          • #14
                            This information is very timely as i am abt to get into my carbs jetting.I have a MAC 4 into 1 exhaust with 4 individual pod filters...so according to the formula stated above...2 jet sizes for the 4 to 1 and 3 jets for the k/ns' minus one comes to 4 jet sizes over stock.So now all I have to know is what the '82 XJ1100 stock jetting sizes are...or were because last yr I put in Dynojet STG lll jetting kit...and its not right at all So where can I find out what the stock jetting sizes are?
                            1980 XS650G Special-Two
                            1993 Honda ST1100

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                            • #15
                              Mad,

                              Go to Yamaha Parts Lookup. Lookup your bike and click for the carburetor screens. In the window under the graphic scroll down until you find "jet, main" and "jet, pilot" and you will see the stock size.

                              I looked at it for an '82 XJ1100J and it shows the mains as #170, and #47.5 on the pilots.

                              DB
                              I think I have a loose screw behind the handlebars.

                              '79 XS11 Standard, Jardine 4/1, Dyna DC1-1 Coils, 145 mains, 45 pilots, plastic floats - 25.7mm, XV920 fuel valves, inline fuel filters, speed bleeders, Mikes XS pods, spade-type fuse block, fork brace, progressive fork springs/shocks, manual petcocks, 750 FD, Venture cam chain tensioner, SS brake lines

                              Comment

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