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Honda GB500 thread

Discussion in 'Old's Cool' started by Spurlock, Aug 27, 2016.

  1. Papacycle

    Papacycle n00b

    Joined:
    Sep 22, 2016
    Oddometer:
    4
    I am new to this site and looking for advice. Have 1990 gb500 with supertrapp muffler; exhaust pipe indicates running lean. Need advice on proper carb adjust or a commercial carb jet kit. Any suggestions?
    Papacycle
    #81
    bran.c likes this.
  2. bran.c

    bran.c Adventurer

    Joined:
    Sep 10, 2016
    Oddometer:
    29
    Hi
    Have the fitting instructions for supertrapp exhaust, mixture screw 2 1/2 turns out and main jet increased fron 142 to 148.
    Hope this helps
    #82
  3. Spurlock

    Spurlock Long timer

    Joined:
    May 5, 2015
    Oddometer:
    1,996
    Location:
    Vacaville, N. California
    Welcome Papacycle. A couple of suggestions.
    - I would strongly recommend avoiding aftermarket carb kits and buy genuine Keihin parts. Here is one source:
    http://www.pjmotorsports.com/

    Main jets for the GB are jet type 99101-393 listed on this page:
    http://www.pjmotorsports.com/keihin-jets.html#main jets

    Pilot jets are type N424-26 on this page:
    http://www.pjmotorsports.com/keihin-jets.html#pilot/slow jets

    Float valve for the GB is #021-862 and the float bowl O-ring is #021-883 listed on this page:
    http://www.pjmotorsports.com/keihin-mikuni-needle-valves.html#Honda-street-atv-offroad
    PJ's float bowl O-rings are superior to those supplied by Honda in that they are formed in the shape of the bowl and not round. Much easier to install since they don't want to pop out of the groove before you get the bowl screwed on.

    - It is possible to remove the float bowl without removing the carb, but it is not easy. But removing the carb is no picnic either. To pull the bowl I use a 1/4" ratchet with 1/4" socket and a 1/4" hex phillips bit. You need to first loosen the manifold and air box tube clamps so you can rotate the carb a bit either way. Then a couple of different length bits (or different length sockets) to be able to reach all four screws.

    - If you do need to remove the carb you will get the most room to work by removing the battery box, then pulling the air box back away from the carb. But I've settled on doing it leaving the battery box in place since that is much quicker. First remove the front and rear clamp bands completely. Then remove the throttle cables and the cable bracket screwed to the right side of the carb. Next remove the oil catch tank on the left front of the air box (has a single bolt holding it).

    Now remove the three manifold bolts and rotate the intake manifold on the carb about 45 deg. counterclockwise like so:
    [​IMG]

    Now pull the carb back toward the air box and swing the manifold and carb out to the left as pictured above. It's tight but will clear as long as the manifold is turned. Here is another view of the carb part way out:
    [​IMG]

    Turn the carb completely to the left as shown below. Pull off the manifold from the front of the carb. It will seem impossible to fit between the head and frame tube, but just keep trying every angle and height and it will suddenly slip right out. There is only one position where it clears, but when correctly oriented it clears easily.
    [​IMG]

    Putting the carb back in is just the reverse. Plant the rear of the carb in the air box boot like below and force it back as you swing the manifold back in position on the head. The boot will be crumpled up , but use a dull screwdriver blade or bent wire to work it back over the carb as below:
    [​IMG]

    [​IMG]

    -Bill
    #83
    Combatscoot and bran.c like this.
  4. Papacycle

    Papacycle n00b

    Joined:
    Sep 22, 2016
    Oddometer:
    4
    WOW! I hoped I would hear from you. And thanks to Bran C as well. Actually have put 6000 miles on bike in lean condition. Have I damaged beyond repair?
    Papacycle
    #84
    bran.c likes this.
  5. Spurlock

    Spurlock Long timer

    Joined:
    May 5, 2015
    Oddometer:
    1,996
    Location:
    Vacaville, N. California
    Thanks Papacycle. What symptoms of overheating have you seen? Some bluing or at least turning golden color is not necessarily a problem at all. If the bike has good compression and runs well, then just keep up with the oil changes and air filter and you're good. And be careful of compression figures, you need a gauge designed for small displacement cylinders. But in general if you crank the kick starter using your arm and can readily feel the compression stroke, you have adequate compression. Not ideal maybe but plenty adequate to ride.

    -Bill
    #85
  6. MuddyK9

    MuddyK9 Adventurer

    Joined:
    Sep 12, 2016
    Oddometer:
    17
    The last time I had my carb out I replaced the four float bowl screws with Allen/hex head screws. These are fairly easy to turn with a small L shaped wrench while the carb is still in place. It is tight work and takes a little patience, but now I can drop the bowl and replace the jet or floats without having to remove anything other than the crank case breather assembly. Worth doing I think.
    #86
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  7. Spurlock

    Spurlock Long timer

    Joined:
    May 5, 2015
    Oddometer:
    1,996
    Location:
    Vacaville, N. California
    Excellent and practical suggestion Muddy, thanks very much.

    -Bill
    #87
  8. Chet Jr

    Chet Jr Adventurer

    Joined:
    Jun 8, 2011
    Oddometer:
    51
    Thanks for setting this group up.
    I have a very strong interest in GBs and have gained some practical knowledge about them over the years. I consider them a great investment as well as a fantastic bike.

    I have several modified GBs including a Cyclewizard built 662 with cloverleaf head, the original Muzzy 600 project GB, and a highly modified 600 GB based on the Cycle World project.

    I also have numerous low mileage stock GBs and numerous spare parts.

    Looking forward to hearing more from other GB owners.
    #88
    bran.c likes this.
  9. bran.c

    bran.c Adventurer

    Joined:
    Sep 10, 2016
    Oddometer:
    29
    I'm looking for a speedometer if you have one
    #89
  10. bran.c

    bran.c Adventurer

    Joined:
    Sep 10, 2016
    Oddometer:
    29
    Was out on my bike in traffic for the first time the other day and noticed I have a problem with my bike not ideling properly, it either cuts out or idles between 1500 and 2000 rpm, hadn't noticed before as I'd been out on the quiet mountain roads beside me
    #90
  11. Spurlock

    Spurlock Long timer

    Joined:
    May 5, 2015
    Oddometer:
    1,996
    Location:
    Vacaville, N. California
    Thanks for checking in Chet. Now we need to see some pictures of those bikes!

    One of mine is missing the tool tray and cover, any chance you might have one for sale?

    -Bill
    #91
  12. Spurlock

    Spurlock Long timer

    Joined:
    May 5, 2015
    Oddometer:
    1,996
    Location:
    Vacaville, N. California
    A few things to check:
    - check the air cutoff diaphragm for leaks. It is under the small cover, upper right side of carb, with 2 screws and a vacuum tube. Also check the T fitting along the vacuum tube and the tubing itself.

    - Check the carb to engine manifold for cracks, make sure the clamp is tight, and check the oval O-ring between manifold and head. That O-ring is likely flattened if original and should be replaced or at minimum apply gasket sealer as a temporary fix.

    - Adjust the pilot screw. You need to first remove the pilot screw limiter cap or else grind off the "flag" from the cap to allow adjusting it in complete turns. The screw itself is fragile so safest is to use a Dremel tool to grind down the flag enough so it will clear its stop. Then with the engine hot, adjust the screw for best idle speed, then readjust idle down to 1200, then recheck pilot screw, etc.

    Both my GBs will occasionally die upon coming to a stop, and I've never figured out why. Others have reported the same thing. Anyone with a fix for this, please chime in!

    Hope this helps,

    -Bill
    #92
  13. Chet Jr

    Chet Jr Adventurer

    Joined:
    Jun 8, 2011
    Oddometer:
    51
    Hi Bill,
    I have a lot of GB parts but I'm really not interested in selling them.
    The going rate for GB parts is getting really ridiculous so I generally try to trade GB parts rather than selling. It seems a much more reasonable method than charging the going rate.

    I do however try to keep some critical GB parts like fuel tanks available to help keep other GB owners on the road.

    Chet

    Attached Files:

    #93
  14. bran.c

    bran.c Adventurer

    Joined:
    Sep 10, 2016
    Oddometer:
    29
    Thanks bill
    #94
  15. bran.c

    bran.c Adventurer

    Joined:
    Sep 10, 2016
    Oddometer:
    29
    Does the gb500 have the same speedometer as other Hondas?
    #95
  16. Chet Jr

    Chet Jr Adventurer

    Joined:
    Jun 8, 2011
    Oddometer:
    51
    CycleWizard built GB662 with big fin cloverleaf head and custom exhaust.

    IMG_0469.JPG
    IMG_0390.JPG
    #96
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  17. Chet Jr

    Chet Jr Adventurer

    Joined:
    Jun 8, 2011
    Oddometer:
    51
    My GB600 with custom suspension work, LSL super bike handlebar kit, lowered foot pegs, DigiDash, custom LED turn signals etc. etc. Much faster and better handling than my 2015 Ducati! The LSL handlebar / riser kit makes the GB a much more comfortable ride.



    IMG_1717.JPG IMG_1712.JPG
    #97
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  18. Spurlock

    Spurlock Long timer

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    May 5, 2015
    Oddometer:
    1,996
    Location:
    Vacaville, N. California
    Understood, and good on you for helping preserve the runners out there.

    That is one "cool" cylinder head, thanks for posting the photos of the wizard bike.

    -Bill
    #98
  19. Chet Jr

    Chet Jr Adventurer

    Joined:
    Jun 8, 2011
    Oddometer:
    51
    Hi Bran -
    It's my understanding that the GB speedometer is unique. A custom speedometer or other model speedometer could be setup for practical use.

    What's wrong with your speedometer? There are shops that could possibly rebuild it.

    Correction edit!
    Please note - I just noticed that you are in Ireland not the USA. You might want to check for a speedometer off the XBR Honda - I believe they are very similar and might be a good replacement .
    #99
    bran.c likes this.
  20. Spurlock

    Spurlock Long timer

    Joined:
    May 5, 2015
    Oddometer:
    1,996
    Location:
    Vacaville, N. California
    Looks like a Batson exhaust?

    -Bill