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Thread: The Unofficial SmartCarb Tuning Guide

  1. #1101
    Lifetime Team KTMTalk bjackson's Avatar
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    Default Re: The Unofficial SmartCarb Tuning Guide

    Quote Originally Posted by Wrightweld View Post
    I just recently purchase a 38mm cast SC. Itís brand new but never ran allegedly. Itís a B casting carb, and my question is around the mr, the paper work I have with the carb says it has an r-076a in it Iíve looked through most of this thread and I canít seem to find any reference to this rod itís all Q11, q9 etc.
    Iím intending to run this in my 2015 300xcw, so Iím just trying to get some baseline numbers.
    Iíve reached out to TE for some info as well, but I thought I would check here too as this is an amazing wealth of knowledge.
    Thanks for any help.
    That's an early metering rod designation, before they used the current numbering system. The "076" is the rod's diameter at the tip. measured at the very end of the rod and across the flat. So it's .076 inches in diameter at that location. That diameter is associated with the A-Q07 rod in the new numbering system.

    I don't know what bike/engine/mods your newly purchased old carb was set up for, but if you are running it on a 2015 300 XCW, it will most likely be rich. You are likely to need an A-Q11 (.080 tip diameter) or an A-V11 (same tip diameter, but a different grind angle that comes into the fuel a little more slowly than the A-Q11).

    Where are you located, what octane and kind of gas are you running (no ethanol), oil mix ratio, engine mods, etc, etc. Once we know that we can make a recommendation (probably an A-Q11). Or better yet, give Nathan a call at Technology Elevated and get his recommendation.

    Barry
    Barry
    When I arrive at my grave I want it to be because I was in a full-on foot draggin' power slide into the hole and my bike landed on top of me. My heirs can dig me out, turn me to ashes and spread them on my favorite trail.

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  3. #1102

    Default Re: The Unofficial SmartCarb Tuning Guide

    Itís going onto a stock 15í 300. 60:1 premix with 91 octane.
    Calgary Alberta, so I assume the fuel is good.
    Yes Iíve started discussions Nathan, now Iím trying to decide if itís worth updating this unit or just cutting my losses and go with a new model.
    Itís 38cab00159, so I assume it was made early in the b production run.
    Last edited by Wrightweld; 06-11-2020 at 11:17 AM.

  4. #1103
    Lifetime Team KTMTalk bjackson's Avatar
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    Default Re: The Unofficial SmartCarb Tuning Guide

    Quote Originally Posted by Wrightweld View Post
    Itís going onto a stock 15í 300. 60:1 premix with 91 octane.
    Calgary Alberta, so I assume the fuel is good.
    Yes Iíve started discussions Nathan, now Iím trying to decide if itís worth updating this unit or just cutting my losses and go with a new model.
    Itís 38cab00159, so I assume it was made early in the b production run.
    The SC2 is a very nice performer. I would guess that you could sell the Cast 38 for close to what you paid for it, but I'm not that familiar with the re-sell market in Canada.

    Barry
    Barry
    When I arrive at my grave I want it to be because I was in a full-on foot draggin' power slide into the hole and my bike landed on top of me. My heirs can dig me out, turn me to ashes and spread them on my favorite trail.

  5. #1104

    Default Re: The Unofficial SmartCarb Tuning Guide

    Just a head's up for anyone with an SC2... when changing the throttle tube I have noticed that when the throttle end cable is disconnected, the cable can thread back down the SC2 slide and get caught up somehow causing the slide to stick open. This has happened to me twice now when doing a grip/throttle tube change. I've had to pull the airbox off the carb and fiddle with the slide to get it unstuck. It's just fluke that I even noticed it. Had I started the bike it would have revved to high heaven.

    Could there be a better design for the cable retainer on the SC2 slide? The current design makes me a bit nervous.

  6. #1105
    Lifetime Team KTMTalk bjackson's Avatar
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    Default Re: The Unofficial SmartCarb Tuning Guide

    Quote Originally Posted by SoftOption View Post
    Just a head's up for anyone with an SC2... when changing the throttle tube I have noticed that when the throttle end cable is disconnected, the cable can thread back down the SC2 slide and get caught up somehow causing the slide to stick open. This has happened to me twice now when doing a grip/throttle tube change. I've had to pull the airbox off the carb and fiddle with the slide to get it unstuck. It's just fluke that I even noticed it. Had I started the bike it would have revved to high heaven.

    Could there be a better design for the cable retainer on the SC2 slide? The current design makes me a bit nervous.
    Any time the cable slack is allowed to become loose, either by adjustment or by changing the throttle tube or by just disconnecting the cable from the throttle cam, there is a risk that the cable can be slack enough to release from the center hole in the slide (the one that the retainer washer guides the cable to in order to insure proper centering).

    Excess slack for any reason can allow the cable nib to 1) fall out of its center hole and get caught by the machining ridge that's intended to closely fit the nib's diameter, or 2) allow the cable and its nib to completely disengage from the center hole in the slide and when pulled back up, especially if the cable is slightly bent near its end, it can re-seat in the cable insertion hole (the one thats off-center) and cause an off-center pull of the cable nib.

    When the nib is in the off-center hole, it will use up any existing slack and stick the nib in the off-center hole, causing a high positioning of the slide, if not corrected. I've seen this happen paricularly when the cable is slightly bent, allowing it to slip across to the off-center hole when it has a lot of slack.

    My cure is simply to pull the slide (a 3-minute job on my KTM 300s) any time I'm changing throttle tubes or grips so I can verify that the cable slack is proper and the cable and nib are guided into and fully seated in the center hole of the slide and it is properly held in place by the cable retaining washer under the slide's cable return spring.

    This is not new to me as I have learned this lesson over the years with many different carb brands. For me, now, it's just habit.
    Barry
    When I arrive at my grave I want it to be because I was in a full-on foot draggin' power slide into the hole and my bike landed on top of me. My heirs can dig me out, turn me to ashes and spread them on my favorite trail.

  7. #1106

    Default Re: The Unofficial SmartCarb Tuning Guide

    Thanks Barry. I didn't realize this existed with other carbs. This has only ever happened to me on the SC2. Good to know for next time but there has to be a better design? Maybe making a bottom-out slightly below the cable holes so that if the cable does go slack the chances of it getting bound up or coming out the other hole is minimized?

  8. #1107

    Default Re: The Unofficial SmartCarb Tuning Guide

    Thanks Barry. I didn't realize this existed with other carbs. This has only ever happened to me on the SC2.

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