Loss of power

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  • dustinroth
    #1

    Loss of power

    Hey guys, new to the forum and new to working on motorcycles... so bear with me a little bit (major new guy here.) I've only had the bike about 4 months and don't know too much about the history before I purchased it. Ran great up until about 2 weeks ago.

    The bike: 1979 GS750

    The problem: Loss of power and acceleration and backfiring.

    So the bike was running fine until one day after a long ride the bike started lurching and lunging at the end of the day. I thought it may have been a gas issue (was pretty low at the time) but I filled up and it kept doing it. Also, when I filled it up it started back firing a little bit.

    Here's a list of things friends have suggested doing, all done and still having the problem:

    Drain carbs checking for water or anything else besides gas.
    Cleaned air filter.
    Sprayed carb cleaner in the air intake.
    New fuel filter

    New symptom occurred on Thursday night, the bike died on the freeway coming home, figure this might be a fuel delivery problem because it started right up the next day. Since I just replaced the fuel filter probably looking at the petcock?

    What's my next step/s here?

    Thanks for reading.
    Tags: None
    • Seana23
      #2
      Hi babes. Erm.... And Gals, I'll have you know.
      There are a few.ov us "Lumpy-jumpered, Spanner Monkeys" out there...

      Sounds like your right about it being a fuel issue...
      I think you've sucked rust and stuff into the carbs when the fuel got very low...

      Either that or the inline filter has got a bit blocked, restricting the fuel flow somewhat.

      Id start at the cheapest thing (new filter) and if that doesnt cure it, then try starting it and spraying carb cleaner into all 4 carbs whilst revving the engine quite hard, this may dislodge whatever has got in there...

      If this doesn't help, then get a manual and start stripping......
      .....the carbs that is.
      Go.steady and do one at a time so you dont gets bits mixed up. Dont split the rack ov carbs though, keep them all together as its easier.

      Its possible to dip carbs in a fluid to clear all the airways etc or get them ultra sonically cleaned but i always find a very thin piece ov wire and maybe some compressed air pretty much does the trick.

      It could also be stuff partially blocking the fuel tap again, restricting the flow into the carbs so you could check that too.

      So, Fuel Tap...
      Inline filter...
      Carb spray...
      Carb strip...

      Good.luck.
      It may look.like a nightmare but if you take it easy and keep focused, it'll go swimmingly, I'm sure.

      Xxx
      I'd take the carbs off and dismantle them and get the rust out.

        Comment

        • steve murdoch
          Forum Guru
          Past Site Supporter
          • May 2004
          • 8507
          • St. Catharines, On.
          #3
          I agree, probably dirty carbs but one real easy thing to check first is a clogged vent hole in the gas cap.
          2@ \'78 GS1000

            Comment

            • Steel Toed Tank
              #4
              Oh yeah, I want a "Lumpy-jumpered, Spanner Monkey"

              Sounds like a load of fun, lol.


              Tank

                Comment

                • Guest
                  #5
                  Is it possible you got the points wet? (ignition)

                    Comment

                    • Seana23
                      #6
                      Originally posted by chef1366
                      Is it possible you got the points wet? (ignition)
                      What? With all this talk ov Lumpy-Jumpered Spanner-Monkeys???

                      Xxx


                      Sorry, couldnt resist that one?
                      X

                        Comment

                        • Guest
                          #7
                          Might also pull your petcock to see if the filter on the petcock has been clogged.

                            Comment

                            • Guest
                              #8
                              You might have a band-aid on a dirty wound. The fuel filter is not going to solve a fuel delivery problem, get rid of it. It should not be there in the first place, it's just closing the door after the horse is out of the barn. Either it is too small to deliver enough fuel, or if it's big enough there is not enough space to mount it without risking kinked or collapsing fuel lines, and the rust and junk in the tank has already blocked the petcock screen or borked the carbs.There is only one way to solve the problem. Clean, flush and seal the tank, clean the petcock filter screen and petcock and rebuild the carburetors (disassemble, soak in carb cleaner and replace the O-rings). Skip one step, and it's just going to happen again. As chef1366 pointed out it could also be ignition related, so bite the bullet and take it off the road until you can do the required maintenance that has been deferred for 30 years.

                                Comment

                                • dustinroth
                                  #9
                                  Awesome thanks for the help guys! Sounds like I gotta clean the carbs and the petcock... I have a fun day ahead for me!

                                    Comment

                                    • Flyboy
                                      #10
                                      Oh yeah, I want a "Lumpy-jumpered, Spanner Monkey"
                                      Hey Tank, you mean like mine?



                                      Dustin, be under no illusion, there is only one way to do it, and that is the right way, short cuts and work pasts ain't going to do it, all you are going to do is give yourself days and weeks of aggravation, trust me on this.
                                      What needs doing is the carbs need taking off, stripping, and I mean every last nut and bolt, jet and circlip, yes split them off the rack, then dip them for 24 hours an clean, clean, and clean again, when you are sick of it and think they are as clean as they ever could be......clean them again.
                                      Replace all the O-Rings, you can get hem from a forum member here at cycleorings.com, for a few bucks, no need for over priced kits that are junk anyway.
                                      While you are in there, replace the intake boot O-Rings as well, dollar to a dime, they are hard and brittle and don't seal well any more.
                                      Check your airbox, if you still have one on, and make sure it seals properly and there are no leaks, and air getting in downstream of the filter.
                                      use weather strip to seal as required, correct vacuum is important.

                                      Check your fuel tap for proper operation, there are two pipes on it, one supplying fuel to the carbs, the other smaller one which takes vacuum from the intake to open the diaphragm.
                                      with the tap set to PRI the fuel should flow freely.
                                      With the tap set to ON or RES there should be no fuel flow, suck on the vacuum line and then the fuel should flow freely, anything else means you have a problem there.

                                      Now, seeing as you never came in through the front door, you would not have received Basscliff's world famous, Mega Welcome, packed with all the GS knowledge and advice you could ever digest or need in your life, including a full colour, with music and dancing girls, step by step tutorial on cleaning and rebuilding the carbs, as well as a list of the necessary maintenance which needs doing on a 30 yr old bike.

                                      So for your sins, I am going to chase you back to the GS owners section to introduce yourself, and put up a few pics of your ride, we love pics, lots of them.....
                                      then Basscliff will be along shortly with the welcome wagon.

                                      Oh, and welcome, by the way.

                                        Comment

                                        • Seana23
                                          #11
                                          SHR HASNT GOT A LUMPY JUMPER... and nowhere to hide one either!!!

                                          Blonde Spanner-monkeys give us Dreddy haired Spanner monkeys a bad name... Always stopping to redo nails and lips!!!

                                          Xxx

                                          Anyway... What the hell is she working on... A park bench!!!???

                                            Comment

                                            • Flyboy
                                              #12
                                              Hahahaha, oh dear Seana, we love you dreddy haired, lumpy jumpered spanner monkeys just the same.


                                              My bed, the one she broke last weekend.

                                                Comment

                                                • Seana23
                                                  #13
                                                  Originally posted by Flyboy
                                                  Hahahaha, oh dear Seana, we love you dreddy haired, lumpy jumpered spanner monkeys just the same.


                                                  My bed, the one she broke last weekend.
                                                  Hahahahahahahaaaa
                                                  Bless you Monkey-man...

                                                  Xxx

                                                    Comment

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