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Thread: disc have alot of black soot

  1. #1
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    Default disc have alot of black soot

    05 FLHTC 88ci with zippers stage 1 max flow filter S&S 551 cams n a supermeg 2n1 running open cap with 4 disc plugs look good but disc have what seems to be a lot of black soot is this normal

  2. #2
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    Excessive exhaust residue is usually an indication you may be running a little rich. You may want to consider adding 2-3 discs for more exhaust flow.

  3. #3
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    will adding disc help with final drive top end because this pipe so far doesn't have the upper range power or pull of the true duels I had on the bike before not much throttle response past 3400 rpms

  4. #4
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    Yes.
    Adding discs will provide more exhaust flow.

  5. #5
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    what are the characteristics of installing to many disc or having to much exhaust flow I know there will be a lack of TQ on the bottom end but will the top end fall off as well...... would I be better off using a closed end cap configuration n if so how many disc....... Is the performance a better balance with the closed end cap
    Last edited by hdcyclenut; 04-20-2015 at 08:00 PM.

  6. #6
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    Quote Originally Posted by hdcyclenut View Post
    will adding disc help with final drive top end because this pipe so far doesn't have the upper range power or pull of the true duels I had on the bike before not much throttle response past 3400 rpms
    Did you also adjust your AFR/jetting/fuel mapping when you added the SuperTrapp and thus the soot? SuperTrapp has a long successful history with Harley Davidsons on flat tracks, so to say that a SuperTrapp is making less power than another exhaust doesn't sound right at all. If you can give some specifics on how many diffusers you're using and what fueling modifications you've made or what jets/fuel mapping the bike has now, I bet the SuperTrapp gurus will get you pointed in the right direction.

    Even on my two 899cc/55ci inline four sportbikes after a combined 80K miles, my diffusers do not show signs of collecting soot, have required virtually no maintenance and deliver power as advertised. Of course though, I followed their online FAQ, started with 6 diffusers, went to 8, then 10, and 12, experimenting with how the bike delivered power at the various points. I ended up noticing that my bikes liked the range of 7 - 9 diffusers. Seven worked best for stock jetting and nine for after the bikes were jetted. Adding more diffusers didn't do anything for top or mid-range, for my jetting.

    Most of my riding is above 4,000' AMSL. I began with the stock muffler and jetting in 2008 and had many problems with the bike accelerating once it got above 7,000' AMSL. With a little fiddling, she'll now pull redline in top gear at nearly 5,000' AMSL and doesn't seem to have any weaknesses even going as high as 9,000.' Pictured is her at the track near sea-level running 9 diffusers and still using the high altitude jetting. Ran the bike all day long, no problem. Would have picked up more top end had I rejetted the mains a size or two higher, but I really wasn't interested in making the bike as powerful as possible. It's already too fast for my skills. As it was, it was pulling through 135 MPH on the main straight. Not bad for a heavy old school 900 when the much lighter fuel injected 750s were doing about the same.



    I'll vouch that there is power and improved throttle respond to be had from a well tuned SuperTrapp.

  7. #7
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    bike is a 05 FLHTC 88ci mods are dynojet T side #48 pilot n 185 main zipper 3" max flow stage 1 S&S 551 cams and supermeg 2n1 open end cap with 6 dics now

  8. #8
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    That's good. It appears the stock jet is a #175, but I cannot find if the carbs are made by Mikuni or Keihin or HD or what. There is the hint too that the pilot jet is a #42.

    The reason for knowing specifics on who makes the jets is important, but only if the jets aren't made by the same manufacturer. So, for instance, if the #185 you have now is made by Dynojet and the stock #175 is a Keihin, those are apples to oranges. Mathematically a #185 is only about 6% bigger than a #175, but by manufacturing disparity, a Dynojet #185 is like putting in a Keihin #210, which would make the jump in fueling +20%. Even 6% is quite substantial, but 20% would make your bike's top end completely fall on its face.

    From my tuning experience, an easy sweet spot power gain is found at +3% and there's the assumption that OEM jetting is always done for optimal sea-level operation. If you live in Denver, CO. (5,000' AMSL), that would make a big difference too. Elevation counters OEM jetting by about -8% for every 4,000' AMSL.

    When you stated earlier that the bike didn't have the upper range power, was that comparing to when the bike was unmodified?

  9. #9
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    Interesting too, from what I'm reading about the S&S 551 cam is that it's a "mid-range" boosting cam. Peak torque is at 3,100 RPM with replacement higher compression pistons.


  10. #10
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    carb is a Keihin HD carb with a dynojet carb kit n thunderside pilot jet is #48 main jet is a dynojet #185 stock carb set up was pilot jet #45 n main #180. All mods were done much before the supermeg was installed n the bike was good on top end. most of my riding is done in MD WV PA VA

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