XR500 versus XL500 carburetor

I inherited two carburetors with the Basket Case, one belonging to an XR500 motor and one to an XL500, and I am curious what the differences between these units are.  Here are my findings.

Both carburetors are piston valve 35mm KEIHIN with a main jet of 150 (factory 155) and a slow jet #55.  The model designation is PD11B for the XR and PD07A for the XL.  For both units, factory position for the needle jet clip is the 3rd groove and the initial pilot screw opening is 2 1/4 turns.

While rebuilding the XR carburetor I observed only two main differences between the two units:

1. Choke
The XR carburetor has a manual choke lever directly mounted on the left side of the carburetor body while the XR carburetor has a remote cable operated choke with the cable attachment mounted on the right side of the carburetor body (see picture below).

Rebuilt XR KEIHIN carburetor on the left and “as found condition” XL KEIHIN carburetor on the right.  Note the choke lever mounted directly on the XR carburetor while the XL has a cable mechanism mounted on the right side (left side of the XR carburetor displayed in the above picture and right side of the XL).

Left side of both XR and XL carburetors displayed here.

2. Emulsifier tube (needle jet holder)
The XR emulsifier tube has 4 additional holes when compared to the XL.  This could be a custom modification done by the previous owner(s) to reduce plug fouling and lean the mixture. Not sure yet, will need to investigate.

XR emulsifier tube on the left, XL on the right.

Next step, let’s compute the main jet size, jet needle position and pilot screw opening, taking into account average ambient temperature and elevation.

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19 Responses to XR500 versus XL500 carburetor

  1. H. Fritzer says:

    Hello Mike,

    I LOVE your project!!!!!!!

    • Mike says:

      Thanks mom, still having fun after all these years getting my hands greasy noodling around engines and motorcycles. And you know it better than anyone, it all started in the mid 70s with the “velomoteur”… 🙂

  2. Khris says:

    Hello Mike,
    Nice project. I was searching for a part for my 82 XL500 an came across your website. I broke the black plastic choke cable attachment to the carb, which is in your picture #1 on the right with the red arrow. Would you be interested in selling this? Thanks

    • Mike says:

      Will be happy to sell it to you — but am in Europe now, and back in Colorado in July. Can you wait until then? Otherwise, there is always eBay…

      • Khris says:

        Hello Mike,
        Thanks for the quick reply. An update- I have not been able to locate the part on e-bay (or elsewhere) yet. I will keep searching, but may have to take you up and wait until you return. Enjoy your trip and I hope you get a chance to ride over there!

  3. noahbamf says:

    Hello Mike,
    Need some help. I pulled my 79′ xr500 out of the garage yesterday and changed oil, spark plug, gas etc. I got it to start, however, whenever i go to push the choke in the engine cuts out. Ive been to my local motorcycle shop and they’ve told me to clean the pilot jet but all I can take out is the main jet and needle jet( I cleaned both). Just wondering if you could give me some tips and possibly post a pic up of the jets sitting in the carb so I could identify which one the pilot jet is. Thanks alot!

  4. Mike Hughes says:

    Hi Mike,
    I have an ’82 XL500 and the carb is is in bad shape. Dipped it in the sonic bath, new diaphragm, which was almost impossible to find and didnt fit all that well when installed anyway. The carb doesn’t have a C clip position, one spot only. Anyway, loved your bike and I have a question for you. I’m going to just buy a new carburetor and I asking you what type/kind/size would you recommend for my bike. I’ve already spent about $1,500 restoring this thing and this will be the last thing I need to buy. I put new rings, new cross hatching, valves in spec, tried every position on the air bleed screw on the carb 3/4 to full throttle it bogs horribly. So, a new carb…any help here would greatly appreciated.
    Thank you,
    Mike Hughes

    • Mike says:

      Hello Mike — “Cleaning” the Keihin carb which comes standard with the XL500 is a challenging task, one that has actually frustrated me. I tried just about everything, including ultra sound and detergents, which will either give you cancer or cure it, and the end result was disappointing — friends have confirmed going through the same rollercoaster ride trying to bring old carbs back to life. I ended up buying another carb on eBay which looked a lot better to begin with (no water induced corrosion). Right out of the gate it was significantly better than the original one and is still the carb on the bike today. So my recommendation would be not to go too fancy or exotic and stick with the Keihin, the model with the remote cable operated choke for your XL. Here is a link to eBay where you can monitor the flow of carbs for sale and pounce on one that looks right for you, and at a price point you agree with (some vendors appear to be thinking that they are selling gold plated carbs).

      • Mike says:

        Wow, Thanks so much Mike. Great reply help. I’ll keep an eye out for one for sure. Riding weather is coming around(South West Washington State) and I wanna ride this baybee. Didn’t get a chance to last summer. Thanks again Mike, take care and GREAT LOOKING 500 you got there.

        Mike Hughes

  5. Tyler Kilp says:

    hey thanks for your awesome site!!! i came across it looking for jetting specs for my XR500. I also got a basket case of a bike to rebuild. will be using this as my reference for the most part thanks so much!1!

  6. Greg says:

    Thanks for the info and a great page to reference. I’ve had my 82xl500r since 1997, been sitting in my parents barn since 2000. Just brought it home last weekend and am very anxious to get it going again and ride it, it’s still pretty good shape!
    Main problem is the carb. The throttle slide was stuck in the body, freed that up, but there is also massive corrosion everywhere inside it, I don’t think it could ever be right again. I have one coming off ebay that looks nice and even has a video showing the bike running well with it. I’m very hopeful for this since parts aren’t exactly readily available for these anymore.
    One thing I noticed looking through the parts diagram, the 82 XL500 was a little different. They either used a 135 main, or a 128 depending on engine number. I’m assuming the jet tube must be a different size for the mains to be so much smaller, or the needle, but didn’t look that far into it. I’m going to see what jets it has in it before I install. The 82 XR has different jets from this even. Maybe another possibility is that the airbox on the 82 XL is unique to that bike only, I know this can play a part also.
    wish me luck. Greg in MN

  7. This is a great tip particularly to those fresh to the blogosphere.
    Short but very precise info… Many thanks for sharing this one.

    A must read post!

  8. Max says:

    Hey Mike, Hope you get this! Awesome build on your 500! On your carb. does your choke have a choke plate spring?? My choke flap just goes loosely and has to be held by hand. I can keep it in the up position with the lever, but when needing the choke, there is nothing keeping it closed! Its for an XR also. Thanks!

  9. Andrew says:

    Hi i just bought a 79 xr 500 and need to know specs on the carb tuning knob if any info it would be appreciated

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