DR650 Carb Operation

Discussion in 'Thumpers' started by aburne04, Jan 23, 2010.

  1. aburne04

    aburne04 Adventurer

    Joined:
    Feb 28, 2009
    Oddometer:
    16
    Location:
    Newcastle
    Ladies & Gents,

    I'm after the advice of the engineers and mechanics amongst us, cause I've definitely got no idea!

    I'm about to shim the needle on my '08 DR650. I've got no problems in doing the task but I'm struggling to understand a part of the concept. A lot of places describe it as "raising" the needle, but by my understanding putting washers in would actually lower the position of the needle?

    I'm looking at the diagram in the service manual on page 4-8 and it just looks to me like adding in washers would reduce/restrict the amount of fuel/air mixture! Obviously this is not the case, so I guess I'm just asking for a little helping in understanding before I go ahead and do this.

    Cheers,
    Andrew
    #1
  2. eakins

    eakins Butler Maps

    Joined:
    May 29, 2002
    Oddometer:
    21,638
    Location:
    Fort Collins, Colorado
    the dr has a CV (constant velocity) carb

    a washer raises the needle by making it sit higher up in the carb slide & overall in the carb.

    as the slide goes up more air and gas pass through the carb.

    so this needle goes down into a tube where gas comes up from the lower floatbowl. gas flows through this tube & into the main carb body & mixes with air.

    the needle sits in an assy called a slide. it comes out of the bottom of the slide and sticks in that tube. as the slide comes up so does the needle effectly unblocking the tube and letting more gas come through the tube.
    the needle is tappered so the gas entered is progressively more as it's raised vrs all gas or no gas.

    in it's current position it will allow so much gas to passby depending on where the slide is. as the slide goes up so does the needle at the bottom and thus more gas (richening the mixture of gas/air).

    if you push up a small washer (same ID as the shaft of the needle) from the bottom (pointy end) up to the circlip (circlip looks like a C and is in the groove) and then put that whole thing in the slide through the hole and out the bottom (and then the white plastic piece goes overtop the circlip and then the spring, which gives it tension) you will find the needle is sitting up higher (in the inside) of the slide. since the needle is sitting higher in that fuel tube, more fuel comes out to power the motor. if you add 2 small stainless steel washers, like i did, it will sit up in the slide that much more and let that much more gas pass through the tube (at the bottom of this tube is the main jet and it's hole size is the limiting factor for max gas through the carb) into the motor.

    people also drill the slide. your slide has 2 holes at the bottom. 1 in the center where the needle comes through. the other to the side of it. people drill an exact same hole on the other side. the slide (& thus needle & more gas) is raised by vacum. this small hole is for the vacum. when you add another hole vacum is greater and the slide moves up faster thus the enginer revs quicker.

    you have another area where gas gets to the carb body & then the motor called the pilot jet. in stock form it's plugged because of the epa and is set lean. it's a brass plug that caps this pilot jet screw. to fix the problem it get drilled out and then the screw is turned out 2 turns (factory is aprox 3/4 turn). by turning this out you get more fuel from zero to 1/3 throttle. from 1/3 to max the fuel metering moves over to the main jet (ie the slide & needle)

    to recap a properly tuned dr card will need
    -the jet sizes are NOT changed.
    - 1 to 2 washers under the needle circlip to raise it for more fuel
    - the slide needs an additonal hole drilled in the bottom to it has greater vacum and thus rises quicker (faster revs)
    - the pilot jet screw plug needs to be uncapped and the screw needs to be turned out 2 turns (turn it in all the way till it lightly seats and then turn out 2 turns). an adjustable fuel screw from kientech replaces the stock pilot jet screw and has a knob on the bottom. with this you can reach under the carb and easily adjust it to fine tune for elevation changes. if you go up in elevation you find it might need only 1 turn out (less fuel) for the engine to run properly.
    -i would also remove the rubber snorkle air inlet on top of the airbox for some more matched air coming in for the extra fuel.


    ---------------
    others will do a different Dynojet carb tune with different needles (shape is different for more fuel) and larger jets (more fuel) along with cutting open the top of the airbox. i've tried this and found it makes more power however this tuning was sensative to elevation changes (which i make alot of). i also found the power to come on to abruptly vrs the linear power the above mods make. many are happy with dynojet. i along with other were not. some had surging problems. try the above mods first and see how you like.

    as a side note, some adjust the legnth of the tension spring on the slide to make the bike rev quicker. results are inconsistent whereas drilling an additional hole in the slide has consistently possitive results. i'd skip this mod.

    others still put on different carbs from mx bikes. these make max power, however use more fuel & are more sensitive to elevation changes.
    #2
  3. aburne04

    aburne04 Adventurer

    Joined:
    Feb 28, 2009
    Oddometer:
    16
    Location:
    Newcastle
    eakins thanks very much for taking the time to post such a lengthy reply! It all makes sense now, appreciate it. I was going to order a DJ kit but I'll try your suggestions first. I removed the snorkel at 1,000km and now its up to 9,000 so I figure it's time to get a bit more out of it.

    Thanks again.
    Andrew
    #3
  4. aburne04

    aburne04 Adventurer

    Joined:
    Feb 28, 2009
    Oddometer:
    16
    Location:
    Newcastle
    Interestingly I've just looked at the bike and it doesn't seem to have the brass cap. I bought it new I wonder if the dealer removed it and has already richened the bike? Or do Australian models not come with the cap?
    #4
  5. eakins

    eakins Butler Maps

    Joined:
    May 29, 2002
    Oddometer:
    21,638
    Location:
    Fort Collins, Colorado
    might not. our epa is tight whereas you have bikes (wr450f etc) that are street legal that are off-road only in the us.
    #5
  6. grub

    grub Requires Supervision

    Joined:
    May 15, 2009
    Oddometer:
    2,244
    Location:
    Waiting for a green light on the red line
    and from this post I also learned that when I need carb work I will come to Eakins house with a six pack...

    #6
  7. Tiggleswerth

    Tiggleswerth Jansport

    Joined:
    Nov 11, 2007
    Oddometer:
    235
    Location:
    Just across the river from Marsing, Idaho
    My carb is stock right now except I have adjusted the pilot jet, and I am unhappy with the mileage I am getting, around 39 mpg on dual sport rides...
    I have need to shim the needle and drill the slide, but it seems like if I shim the needle and it lets more fuel in, I will get even worse mileage. Am I wrong, or will shimming the needle make the bike run cleaner and get better mileage? It seems counter-intuitive. My exhaust is stock and I have a twin air filter. Thanks for any help!
    #7
  8. Tiggleswerth

    Tiggleswerth Jansport

    Joined:
    Nov 11, 2007
    Oddometer:
    235
    Location:
    Just across the river from Marsing, Idaho
    any one else in the same boat?
    #8
  9. dljocky

    dljocky Been here awhile

    Joined:
    Dec 6, 2008
    Oddometer:
    884
    Location:
    Yorktown, Va
    Jansport,
    I'm in a similiar situation. I'm getting around 45mpg on my 2009 DR650. My bike was running aweful, I took it to a different dealer, they drilled my pilot jet 5 ten thousandth's of an inch. Shimmed my needle. The bike starts fine now, it warms up in a couple of minutes, and I no longer have to drive around with it on the choke. But, I still get the surging when I'm running 50-60 mph. Everyhting else is stock. I had an 01 DR650, 55 mpg average, and no surging. I'm not sure what to do.
    #9
  10. SOILMAN

    SOILMAN DIRT-HOG

    Joined:
    Nov 29, 2008
    Oddometer:
    500
    Location:
    Gloucester County Virginia
    [​IMG]

    My 450....lots of fun
    #10
  11. SOILMAN

    SOILMAN DIRT-HOG

    Joined:
    Nov 29, 2008
    Oddometer:
    500
    Location:
    Gloucester County Virginia
    [​IMG]

    with some Woody's Wheels and Dunlop 908RR and 606 frt
    Your Suzuki is a nice bike...have you ever considered the new BMW FS800 dualsport? I wish we had more "real" dualsport riding areas close by.
    #11