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Changing Intake ports to a D shape for better flow.

Discussion in 'The Garage' started by Jack, Sep 13, 2019.

  1. ReycleBill

    ReycleBill Part Time Tyrannicide XS650.com Supporter

    17/34 was stock US on '83. Not sure about other years. I'm currently running a 16/32 but want to go to a 17/32 and give it a try. I'm running #520 chain and the last time I replaced sprockets no one had 17s in 520 available so I went with the 16 instead. The 16/32 is great on our Interstates but it just doesn't work well when I put my 220 pound butt plus gear and take off to the Blue Ridge mountains for a few days.
    gggGary, spungle and Bewarethemoon like this.
  2. spungle

    spungle XS650 Enthusiast

    today I finally had the opportunity to compete against another xs. This one has a port and polish head, tm34 carburetor like mine and an original exhaust. No chance against mine, not to compare. Starting point was both side by side, 3rd gear, about 70km/h, then full throttle. Mine is blown off, I saw the other one getting smaller and smaller in the rear view mirror.
    Yes, the comparison is not quite fair, because I have 100cc more and a shell #1, but the difference is already very big, so I think that I have a very well tuned combination of head, camshaft, carburetor and exhaust and the head plays a big role. I hope to be able to make a comparison with a 750cc bike this year... And to have saved money for a dyno run sometime.

    I also have the feeling that the engine wants to breathe more in the upper revs and I should get even bigger air filters.

    We swapped bikes and do the test again. My bike will rev in the 4th gear till death. The other bike felt a bit sleepy in 4th gear upper regions and a lot sleepier in the 5th gear. Big difference, like a different bike.
    Last edited: May 15, 2020
    grizld1, gggGary, Jim and 2 others like this.
  3. Jack

    Jack XS650 Junkie Top Contributor

    That head is a combination of high CFM volume beginning at mid lift for more power down low to max RPM and higher port velocity for improved efficiency and not knowing how this increased efficiency will impact fuel atomization,there's a good chance that a reduction in main jetting maybe required,just guessing here. You need to make a few WOT runs then immediately shut it down to pull the plugs and check the plug coloration.
    This will get you pointed in the right direction for reading plus.
    spungle, Jim, grizld1 and 2 others like this.
  4. Hudriwudri

    Hudriwudri XS650 Member

    First off a kind hello to the Xs community from Italy


    Nice bike you have there, but if you don't mind me saying the info about no return valves on the crankcase, d-shaped ports in combination with the recommendation of the use of of a higher lift reasonably short duration Megacycle or web cam profile has been for years on the German forum.

    Compliments to your nice d ports, don't mind the critics of some people that might not fully comprehend the theory about such (btw very nice looking) d-ports.
    I have been using D-ports, where needed, for decades now and with proven track success on Sr/Xt engines (did not find the time for my Xs engines within the last year's due to work) among several other brands (honda, Ktm, Norton, triumph, and among other mod's even DBD34 Goldie's) and makes.
    The only thing that remains crucial in doing such work is that the cam should be chosen accordingly to the port properties or better said the port should be shaped according to chosen cam profile spec's (mean flow, maximum increment flow which is not maximum flow and maximum flow lift etc etc).
    Kind regards


    Ps: sorry just read it now, spungle, if you don't mind me asking, who welded and how the crank I assume in Germany? Given the fact that the crank and iniin particular the pin is of a higher alloyed
    steel it is important to weld it in a certain temperature releasing / inducing mode in order to not brittle out the HAZ.
    Last edited: Jun 27, 2020
  5. spungle

    spungle XS650 Enthusiast

    Hey Christian, thanks:)
    My crank was rebuild by an reputated member of the German forum. He rebuilded many xs650 cranks for over a decade, if not many more years. He weld cranks for racing (sidecar) xs650, some of them with over 1000ccm. If there were problems with his welding I would know it. The forum whispers such things normaly. I have no technical background. My way is to read, read and read, try to understand, recheck, and look at the expertise from members. Other than that i have to trust them:) And till now it works like a charme:D

    Btw., Last 2 months little time to wrench and final tune my little rocket. Last week I worked the "ported" spigots. The next time I will final tune the carbs. Till know not shure with the mainjet. One size or two size down, I have to figure out now.
    Last edited: Jul 1, 2020
    Jim and Bewarethemoon like this.

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