Announcement

Collapse
No announcement yet.

1982 GS750E will not rev under load

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

    1982 GS750E will not rev under load

    My 1982 GS750E does not want to rev while under load (on the street with rider). It starts, idles and revs to 8K+ RPM on the bench or if I pull in the clutch while in motion. But while riding, it is extremely underpowered and will not rev past 3 - 4K RPM and has no power. See list of what has been done below, educated suggestions are welcomed:
    • Stock exhaust, airbox and new air filter
    • Stock carb settings, recently cleaned and rebuilt (replaced all jets, etc.)
    • Brand new Dyna ignition, coils, plug wires and coil relay mod. Huge blue spark all cylinders.
    • Ignition advance works freely
    • 12.6V to the coils at 3K+ RPM
    • Fuel flow is fine, not a plugged vent on the tank and vacuum line from carb to petcock is fine
    • 160+ PSI compression for all cylinders
    • Does not surge at idle or backfire on decel
    • Plugs appear to be slightly on the lean side, all four look identical.
    • New battery and spark plugs
    • Timing marks on cams align, timing is set, cam chain nice and snug (tensioner works freely) no noise or rattling from top end.
    • Valves are all adjusted properly.


    Need to recheck float bowl levels. Could that make it run fine with no load but like crap when there is a load?

    #2
    Hi Dave that sounds like fuel to me,check float heights maybe some sea foam as well.

    Comment


      #3
      Yep check float heights,if they were too low bike would die when under load !

      Comment


        #4
        Air leaks can cause that
        Did you replace the carb boot or those O rings?
        1978 GS 1000 (since new)
        1979 GS 1000 (The Fridge, superbike replica project)
        1978 GS 1000 (parts)
        1981 GS 850 (anyone want a project?)
        1981 GPZ 550 (backroad screamer)
        1970 450 Mk IIID (THUMP!)
        2007 DRz 400S
        1999 ATK 490ES
        1994 DR 350SES

        Comment


          #5
          The '82 750 doesn't use carb boot O-rings so that can't be it.

          When you replaced the jets where did you get them? And did you take the carbs fully apart as detailed in the carb rebuild tutorial linked in my signature? I'm wondering if the carbs are the problem, maybe some crap aftermarket jets or some passages are plugged?
          Ed

          To measure is to know.

          Mikuni O-ring Kits For Sale...https://www.thegsresources.com/_foru...ts#post1703182

          Top Newbie Mistakes thread...http://www.thegsresources.com/_forum...d.php?t=171846

          Carb rebuild tutorial...https://gsarchive.bwringer.com/mtsac...d_Tutorial.pdf

          KZ750E Rebuild Thread...http://www.thegsresources.com/_forum...0-Resurrection

          Comment


            #6
            Hey All;
            Thanks for the responses! Haven't been here for a bit, too hot to work in my garage. I pulled the head as it appeared I had a head gasket leak (confirmed). I noticed the valve oil seals were leaking so I will be replacing them as well as the head gasket, etc. Since I have the carbs off I will check the jet sizes and also float bowl levels. When I cleaned the carbs I did take them apart and fully clean as per the rebuild tutorial. All passages appeared to be clear.
            The carb kits I used were K&L bought on eBay. Here is their description:
            This listing is for 4 new K&L Pro brand carburetor repair kits for the models listed below (1 kit per carb). These quality Made in Japan parts are fresh stock and ready to install. This 15 piece kit includes all of the standard parts needed to rebuild one carburetor. Please note that this kit includes jet sizes 42.5, 112.5 and 170.

            Comment


              #7
              The KL stuff is not the best. It's better to just change the gaskets & O rings, usually the rest of it doesn't need changing but occasionally you get an bowl valve or something that needs to be replaced... those can be bought OEM.

              cycleorings (Robert Barr) is the place for O rings
              1980 GS1000G - Sold
              1978 GS1000E - Finished!
              1980 GS550E - Fixed & given to a friend
              1983 GS750ES Special - Sold
              2009 KLR 650 - Sold - gone to TX!
              1982 GS1100G - Rebuilt and finished. - Sold
              2009 TE610 - Dual Sporting around dreaming of Dakar..... - FOR SALE!

              www.parasiticsanalytics.com

              TWINPOT BRAKE UPGRADE LINKY: http://www.thegsresources.com/_forum...e-on-78-Skunk/

              Comment


                #8
                Originally posted by DucatiDave View Post
                I pulled the head as it appeared I had a head gasket leak (confirmed).
                I was just about to suggest this as a long shot. My 79 gs750e was acting similar. low gears in town, was ok, but would fall on its face under heavy acceleration or under load in higher gears.

                Comment


                  #9
                  Thanks Mike! I am hoping to get the head work done over the next month or so, will let you know if it helps. Good to hear that this fix helped your situation.

                  Comment


                    #10
                    Just updating to close this out... after replacing the head and base gaskets, rechecking valve clearances, replacing/adjusting the air mixture screw, readjusting timing and adjusting float levels, the bike runs great. I think it was a combination of small problems all contributing to the issue. I still need to sync the carbs to smooth out the idle a bit (not bad now) and then I think I can just ride and enjoy.
                    Thank you all who contributed suggestions!

                    Comment


                      #11
                      Glad to hear you got it sorted.
                      2@ \'78 GS1000

                      Comment

                      Working...
                      X