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Latest post Fri, Apr 27 2018 11:05 AM by FX. 6 replies.
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  • Thu, Apr 26 2018 1:38 PM

    • hale1730
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    • Joined on Thu, Apr 26 2018
    • Posts 4

    1991 Sportster Carb Jetting

    Hello, 

        I recently gave my son my stock 1991 Sportster 883 Deluxe with about 35,000 miles that I have had since it was brand new.  The other day I heard a decent sounding, really loud bike pull into my driveway. It turns out my son took a hole saw to the back of the stock mufflers and removed all the sound dampening and baffling materials in essence making a DIY slip on exhaust dragpipe type setup.  He wanted the bike to be louder. Who didn't at 21 years old? The bike really sounds pretty good with his modification.  I told him we need to rejet the carb since he negated all of the back pressure from the exhaust andit could result in engine damage.  This is where it gets complicated. I've heard 15 different answers from 15 different people as to how the carb should now be set up.  The stock exhaust is unchanged except the removal of the innards. My question is what do I need to change in the carb? ie. needle, main jet, low jet etc. And what do I replace them with? ie. low jet 42, 45, 48 etc.  main jet 150 through 180 etc. and what needle? Specific part numbers of what I need to order would be very helpful too.  We don't need it to be a racer or anything and take it into a shop to get it perfectly computer tuned and spend lots of money.  I just want to be able to change things out at home in the garage to make sure the engine on this old girl doesn't get damaged.  Any information you folks can give me is really appreciated.

    Thanks, Rob

  • Thu, Apr 26 2018 4:04 PM In reply to

    • FX
    • Top 10 Contributor
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    • Joined on Sun, Mar 12 2006
    • Tonawanda NY
    • Posts 5,201
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    Re: 1991 Sportster Carb Jetting

    The engine is running too lean, and you are correct, that can cause damage. There is no set rule for jetting a carb. Every application is different. You only have to change the mid jet to larger. They are not too expensive. I would get the next 2 or 3 sizes bigger. Try each one for a mile or so, then read the spark plugs after each run. The plugs now are probably snow white. You want to get them to look light tan, light gray...

    FX

    Don't force it, get a bigger hammer.

  • Fri, Apr 27 2018 5:24 AM In reply to

    • hale1730
    • Not Ranked
    • Joined on Thu, Apr 26 2018
    • Posts 4

    Re: 1991 Sportster Carb Jetting

    Wow, that could be alot of pulling the carb on and off.  When you say sizes bigger are you refering to the number such as 150, 155, 160 etc? If so any idea what size came stock on the 1991? One jet doesnt seem too bad some guys were saying to change low jet and needle using washers as spacers and making tuning it sound complicated. Thank you for the info.

    Rob

  • Fri, Apr 27 2018 5:28 AM In reply to

    • hale1730
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    • Joined on Thu, Apr 26 2018
    • Posts 4

    Re: 1991 Sportster Carb Jetting

    FX, when you say mid jet, is the the same as main jet or a different one?

    Thanks, Rob

  • Fri, Apr 27 2018 6:46 AM In reply to

    • FX
    • Top 10 Contributor
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    • Joined on Sun, Mar 12 2006
    • Tonawanda NY
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    Re: 1991 Sportster Carb Jetting

    No Rob, the jet you are calling low is actually called the 'mid' jet, you don't have to change the high speed (main) jet. It would have a two digit number, and you only have to drop the float bowl to change it. You can try only buying the next size up, but if that doesn't work, you'll have to order another one, and that would take time, unless you can get them locally. The bike should not be driven much if too lean.

    FX

    Don't force it, get a bigger hammer.

  • Fri, Apr 27 2018 10:20 AM In reply to

    • hale1730
    • Not Ranked
    • Joined on Thu, Apr 26 2018
    • Posts 4

    Re: 1991 Sportster Carb Jetting

    Got it thanks for clarifying for me.  I dug up some specs that said it came with a #42.  Harley is calling this part the slow jet, if this is the same part you are referring to(so many names for the same thing). Attached is the pic of the carb breakdown. Just to be sure, part #15 on the diagram is what I'm supposed to change? If so, I'll order a #45 and #48 just to make sure he's covered.  Sorry for being such a pain in the ass.  I have the most experience working on S&S carbs and never tore into one of these EVO carbs before.

    Thanks, Rob

    Keihin Carburetor Parts

  • Fri, Apr 27 2018 11:05 AM In reply to

    • FX
    • Top 10 Contributor
      Male
    • Joined on Sun, Mar 12 2006
    • Tonawanda NY
    • Posts 5,201
    • Moderator

    Re: 1991 Sportster Carb Jetting

    Yes Rob, #15 is the one you have to change, and you just have to remove the 4 screws to drop the float bowl. That comes on just off idle, and switches over to the main (high speed) at about 3-4 k rpm. Unless he's running the Baha at over 100 mph, there's no need to change that. I wouldn't mess with the needle just yet, jetting is all you should need. The CV carbs are very good, some guys put them on old Shovelheads. No pain in the ass at all Rob, we enjoy helping out.

    Let us know how you're do'n. This is ineresting to all...

    FX

    Don't force it, get a bigger hammer.

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