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My exhaust creation.

Discussion in 'XJ Modifications' started by cds1984, Nov 20, 2016.

  1. cds1984

    cds1984 Active Member

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  2. non_quotidiun

    non_quotidiun Member

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    Looks pretty nice mate.....probably sounds better IRL than the mobile phone recording :)
     
  3. cds1984

    cds1984 Active Member

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    Hi,
    So...
    I have a custom exhaust (https://www.xjbikes.com/forums/threads/my-exhaust-creation.106337/) and basically 31A (XJ900)configuration otherwise.

    The temperature today was 28C and the bike was a beast.
    The temperature yesterday was 39C and it popped and farted and ran like it was a piece of crap.

    Okay, technically it ran like a piece of crap unless i slowly let it wind up instead of just accelerating.

    So...
    Question: I thinking just too lean all over and in the cooler weather I'm good?
    Or do you think I need to look at my pilot jets? (which would suck of course)

    Thanks!
     
  4. Simmy

    Simmy Well-Known Member

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    Wouldn't the hot air make it richer?
    Air less dense when hot, heavier when cold.
     
  5. Yammaat

    Yammaat Active Member

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    Very nice indeed!
     
  6. Franz

    Franz Well-Known Member

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    Weaker if there was less oxygen perhaps?
     
    Last edited: Mar 23, 2021
  7. Minimutly

    Minimutly Well-Known Member

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    Less oxy would make it rich...
     
    Franz likes this.
  8. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    Think about why we need to use the enricher on a cold day.
    Colder air is denser (more molecules per cubic liter), causing the fuel mixture to lean out, so we compensate by dumping more fuel into the airstream until the engine warms up.

    So if she's running fine in the warm and not in the hot, then you need to lean her out a bit. That farting and popping was unburnt fuel lighting-off inside of the exhaust.

    Do a hot-weather run and see what the plugs look like.
    What are you using for an air filter?
    Just changing from the stock paper element to a reuseable foam element might be enough to get the mixture where it needs to be.
     
    Last edited: Mar 23, 2021
  9. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    OK. I merged the two threads so we can all have the same look at the history of the exhaust and what the fueling arrangement was when you first installed it. Even though you linked the thread I'm not sure that anyone re-read it (Including me at first).
    There are clues there. Just enough to start getting me confused.

    You may in fact be too lean all over, but the engine should run fantastic in the hot weather if that's the case. I wonder if the collector box baffling isn't part of the problem. That long center plate may be interfering with scavenging, contributing to the poor running at high temperatures. I could also be entirely wrong about that.

    One thing at a time though, especially since the exhaust takes the most amount of effort to change.
     
    Last edited: Mar 23, 2021
  10. Franz

    Franz Well-Known Member

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    Can you make the mixture leaner in this situation by moving the clip on the tapered needle up a notch? Or is that needle kicking in further up the rev range?
     
  11. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    I'm still thinking that she's rich at this point. The plugs will tell the tale though.
     
  12. 50gary

    50gary Active Member

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    High humidity also = less oxygen therefore richer condition.
    Cheers, 50gary
     
  13. cds1984

    cds1984 Active Member

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    Makes sense! Fat air.
    I will do some plug checks and let you know.
    Thanks for the ideas/help.
     
  14. cds1984

    cds1984 Active Member

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    Pics of my (they all look the same) plugs on a nice cool day 28 Degrees Celsius.
    Hmmm... I like the look of them, what do you think?
    PXL_20210324_140051449.MP.jpg PXL_20210324_140115529.MP.jpg
     
  15. cds1984

    cds1984 Active Member

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    Just did a google conversion on the temperature of the day that it was going nuts.
    In Fahrenheit it was 102.2 and muggy (humid) as hell on the day.

    Crazy the difference between then and now, but it was a few days ago.
    I suppose the real question is what will the plugs look like after another day when it goes nuts...

    Driving me nuts... that's for sure.
     
  16. Andy Dobkins

    Andy Dobkins Member

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    I welded it for 30 years every day building gates from galvanized pipe my boss said its not dangers to weld now have stage 4 lung cancer its from smoking all I hear welding galvanized in a enclosed shop had nothing to do with it.
     
  17. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    Well, she's not running rich.
     
    Last edited: Mar 24, 2021
  18. Yammaat

    Yammaat Active Member

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    Liability-issues probably.
    Metalvapors are VERY dangerous.
    My college had 'weldinglungs' and that delivered some very weird mental situations.
     
  19. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

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    Might not be anything, but here goes:

    EXHAUST SYSTEM OVERVIEW:

    As with many other systems on these bikes, the Yamaha XJ-series of exhaust systems are a mini marvel-to-behold, well thought out and engineered......so please do keep this in mind when considering aftermarket "performance" exhaust systems.

    Let's start with the headpipes: many of them are actually of a double-wall design......an inner tube (that carries that gas) and an outer tube that can stay relatively cooler and thus maintains its chromed appearance much better and longer. Additionally, they are tuned in their internal (gas-carrying) pipe diameter to match the flow characteristics needed for their intended use.....thus, for example, even though the headpipes for an XJ650RJ Seca can physically be installed onto an XJ700 engine, the inner pipe diameters do differ, and thus the swap may cause more harm than good, as it messes up with the balance of airflow thru the engine.

    Pipe diameter helps determines (among other things) both the volume of exhaust gas that can be carried away, and, equally as important, the speed at which those gases will flow thru the pipe. All other things being equal, a bigger diameter pipe --- while surely capable of flowing more gas volume --- will also slow down the progress of gas thru that pipe......which, in the world of exhaust gas flow --- and its important effects on intake gas flow (how well each cylinder can be scavenged of its burnt exhaust gases and allow for a full and complete incoming fuel/air charge) --- is a mighty important consideration.

    http://www.gomog.com/allmorgan/exhaustbackpressure.html


    By the way......although we've touched on some of the reasons above.....in regards to "swapping" headpipes between models, our best advice is: don't. Besides the whole "gas capacity and velocity" issues discussed above, there also the issue of fit: although the headpipes between a 550 and a 750 (for example) may look the same, and may actually bolt onto the cylinders heads, both their length and their unique bend angles ---- needed to follow the frame and mate up with the exhaust collector ---- will likely be different.


    Next: the collector. Although these weren't used on the XJ650 Maxim and XJ1100 models --- those bikes use a crossover pipe to perform the same function --- the collector box performs a few not-so-obvious but very important functions, and does it in a very admirable manner. First, of course, it provides a transition between the headpipes and the mufflers. Second, it keeps the decibel levels down to a reasonable volume. And finally....and very important for overall engine performance.....it provides a method of assisting that all-important "gas velocity" by providing a sufficient volume of space for "warehousing" (temporarily) the exhaust gas volume, while also providing (via its unique design) the ability to assist in providing maximal exhaust gas flow.

    If you've ever looked carefully at your heavy (and probably-rusty) collector, you'll notice that it is designed ("split") in such a way so that cylinders 1 & 4 (the outer two) "share" a certain internal cavity space, while cylinders 2 & 3 "share" the rest of it. This is important because of the firing order of your engine: 1-2-4-3

    If cylinders #1 and 2 --- which fire sequentially (and, thus need to exhaust their spent gases sequentially) ---- were to share the same exhaust cavity, then their (sequential) exhaust gas flows would be "spaced" too close to each other (in time) and would see vastly different back-pressures (cylinder 2, which fires after cylinder 1, would see more back-pressure than cylinder 1, which emptied itself into a, well, into an "empty" exhaust collector).

    To put it another way, cylinder #2 sees a lot more back-pressure than cylinder #1, because the gas pulse from #1 doesn't have much time to exit the system before the pulse from #2 is trying to squeeze itself in the same pipe. Notice that cylinders #3 and 4 have a similar situation.

    The same thought goes for the other two cylinders (# 2 and 3). Notice how even the aftermarket "dual" exhaust systems suffer from the above problem, since they are really two separate system, one system being for cylinders #1 and 2 (left side) and the other being for #3 and 4. Notice how it's the "sequential" problem.....since cylinders 1 and 2 fire (and exhaust themselves) sequentially, and since those gases vent into one common chamber, that cylinder #2 is going to see more backpressure than cylinder #1 will......and same for #3 and 4.

    This un-balanced situation....with different cylinders seeing different exhaust system back-pressures......can (and does) result in different amounts of burnt gas scavenging from the differing cylinders, which is not the way to get an engine to make the most amount of power.


    Aftermarket 4-into-1 systems overcome this "differential scavenging" situation by re-introducing, somewhat, a "collector".......where the fours pipes come together into a common chamber, just before the muffler. This collector allows the system to maintain some amount of equalized back-pressure (and thus burnt gas scavenging), while the particular placement of the four headpipes, as they come into the collector, allows a little bit of "pull-thru" between each cylinder, helping to reduce overall system back-pressure levels, while still maintaining a somewhat equal amount of back-pressure to each cylinder.

    Or, maybe, aftermarket systems do no such thing:

    http://www.motorcycleproject.com/text/exhausts2.html


    Of course, the final piece of the puzzle is the mufflers, which are primarily decorative pieces....they look nice, stylish to the lines of the bike, contribute almost no back pressure to the system, and provide a nice throaty (but not too loud or droning or buzzing) sound output.

    So just remember that the real heavy-lifting in the exhaust system is actually done by the headpipes and the unique, well-designed (but often overlooked) collector box.
     
    Last edited: Mar 24, 2021
    meatbag, cds1984 and k-moe like this.
  20. Andy Dobkins

    Andy Dobkins Member

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    went in about 12 years ago said my iron was off the scale so was my zinc and chromium
     

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