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That’s a heckin big jet.

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  • That’s a heckin big jet.

    So I started the tear down on my project today. I began carb rebuild and the jets are huge. I have a 186 and a 138 and the needle is a 5gl 16. (I forgot to look at the pilot)

    The bike came with pod filters installed and a 4-1 exhaust. I’m curious if anyone know what kind of exhaust it is. I’m not sure if those sizes are correct or not as I have nearly no knowledge of the maintenance and modifications that took place before I bought the bike. The guy who owned it before me was quite knowledgeable however and I think if he put those in there he did it with purpose.

    In the box of left over parts I received is the remains of a dynojet kit and about 10 old used jets as well as a full set of old head studs that lead me to believe that at the very least the head was off at some point, though I could be wrong. The pistons are clean and oily, no rust or carbon deposits from what I can tell by looking through the spark plug ports.

    based on the huge jets And the clean state of the pistons I wonder if the previous owner over sized the pistons. I suppose without pulling the head I’ll never know but man would it be cool to not need to do that.

    also when I pulled the carbs apart today a green fluid poured out of them I’m not sure if it was just fogging oil or some kind of stabilizer. Any ideas?

  • #2
    That’s a good observation on the cleanliness of the pistons. Sounds like they are being fed a more or less proper A/F ratio. However, over sizing the pistons to an 1198 which is the “standard” big-bore for an XS, wouldn’t necessitate much different jetting than a stock bore. Slightly different, yes/maybe, but not a huge difference, not in my experience with other bikes,

    Something doesn’t compute if the carbs had 186 and 138 sizing, even if the 186’s are DynoJet, they are WAY, WAY large relative to 136 Mikuni’s.


    ‘01 ZRX 1200, only bike in the garage.

    2020 Rally Link:


    • #3
      Yeah that’s what I’m saying. Ill double check the carbs model tomorrow when I get a chance. There was a whole second rack of carbs in the box so I guess it’s possible that the PO somehow went up a size? I’m not even sure if that’s plausible. Anyways thank for the info.



      • #4
        You reported earlier that the PO did some oil fogging for the shutdown. That green liquid you found in the carbs and inquire about was probably "sea foam". There are a lot of folks that fill carb bowls with sea foam for storage periods.

        Just my guess.......

        Jetting, lots of misdirection occurs with this topic. The POs were probably playing around a bit looking for the elusive bolt on power. The LG should have Mikuni BS34-iii carbs which work quite well in stock configuration. Starting back at stock settings would probably make your return to operating condition much less problematic. One thing that may haunt your carbs: a common CV carb "performance" mod was to drill out the pressure sense port in the slide bottom face. (This causes the CV slide to raise earlier in the throttle position and introduce the main jet before WOT). At least knowing if its enlarged or not is good to know if you have mid range issue when you get the bike running again.

        80 SG


        • #5
          I think you’re right about going back to oe jet sizes. I’ll look a little closer at the carbs tomorrow. But I’m gonna just order a jetting kit since I’m going to be screwing around with the air box anyways. There’s some really good threads about jetting on here As long as I know what I’ve got to start with.


          • #6
            Originally posted by Bderum View Post

            The bike came with a 4-1 exhaust. I’m curious if anyone know what kind of exhaust it is.
            It appears to be a Mac 4 into 1.
            Marty (in Mississippi)