Announcement

Collapse
No announcement yet.

'81 GS850 Won't Start

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

    '81 GS850 Won't Start

    I know this thread title may wear thin on many members' patience, but I feel like I need some clarification/direction. First a little history:

    The bike ran (sorta) when I bought it, but the PO had to use starting fluid to start it and keep the revs above about 1500 to keep it running. I limped it home and started cleaning the carbs. I soaked them in Berryman's for about 18 hours (all together, used 2 gallons, I have no patience). When assembling them, I realized I forgot to remove the pilot air jet, so I paid special attention to it and the passage in the carb body with the carb cleaner/compressed air.

    I put everything back on the bike and set up an aux fuel supply to run the engine and it wont start. The PO had pods on but said it wasnt re-jetted (and partly why it ran like crap). I put the stock airbox, sealed with weather stripping, back on. It still refused to start until I sprayed a shot of carb cleaner directly into the upper section of the airbox (into the snorkel does nothing). Once it was running, cylinder 1 was not firing (cold exaust) and it died anytime I took the choke off. I replaced the plugs/caps and noticed they were all a little dirty with carbon deposits.

    I am getting spark but now I cant get it to start no matter what i do. It turns over and it sounds like it tries to sputter every couple cranks or so. Feeling frustrated I tested the compression in cylinders 1 and 2 (battery was tired from trying to start it so I only did the LH side) and they were both around 60 PSI and about doubled when I added oil to the cylinders.

    Now here are my questions:

    1. Could the bad rings as suggested by the compression test keep the bike from starting?

    2. If the filter that came with the (used) airbox was WAY over-oiled (as in dripping), would that keep it from starting?

    3. When I re-installed the choke plungers, I used a bit of oil to lube them up. Could that oil have clogged something important?

    4. I have read on numerous threads here that valve clearances being out of tolerance can cause hard starting, but I feel like it should at least TRY to sputter, even though I haven't (yet) adjusted them.

    I'm about to pull the carb bodies off again and re-soak/clean them, but if that doesn't get it started, I'm pinning all my hopes to the valve clearances.

    #2
    #4 wasn't really a question, sorry. Would the valve clearances being out of spec cause it to not start or run at all? BTW this bike has 17.5k miles.

    Comment


      #3
      Fully charged battery and new spark plugs?

      Daniel

      Comment


        #4
        1 y es
        2 yes
        3 yes
        4 yes

        You're on the right track, if it starts with cleaner it has ignition and air. It just needs fuel

        Did you follow the carb cleaning tutorial?

        The valve clearances are important, but that alone won't keep it from starting at all

        THe low compression is probably a combination of stuck rings and tight valves

        Put some penetrating oil into the cylinders to help free the rings
        Last edited by Big T; 09-10-2011, 12:12 AM.
        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
          Originally posted by 7981GS View Post
          Fully charged battery and new spark plugs?

          Daniel
          I have been keeping it hooked up to a battery tender and messing with it once a day so the battery has a full charge. I just put new plugs and caps on it today, although the old ones looked darn near new, save for the carbon buildup.

          Comment


            #6
            Originally posted by Big T View Post

            Did you follow the carb cleaning tutorial?
            Yes, i used o-rings from MrRobertBarr and did everything according to the tutorial. The only thing i missed was the pilot air jet, but I removed/cleaned them upon reassembly. They jets themselves were pretty clean so I feel like the dip had ample opportunity to penetrate the passage.

            Comment


              #7
              Well I went out and tried again before going to bed and miraculously it fired right up with no choke. The only change I can definitively say is that i removed the in-line fuel-filter that (I'm guessing) the PO put in. Next step will be to check out the petcock to make sure the filter element is still good so I can throw away the in-line.

              Its still only running on cylinders 2,3, and 4, but my guess is that has something to do with the low compression (hopefully just a stuck ring) in cylinder 1. Would a proper carb sync possibly cure the dormant cylinder?

              Comment


                #8
                Originally posted by Mattias44 View Post
                Well I went out and tried again before going to bed and miraculously it fired right up with no choke. The only change I can definitively say is that i removed the in-line fuel-filter that (I'm guessing) the PO put in. Next step will be to check out the petcock to make sure the filter element is still good so I can throw away the in-line.

                Its still only running on cylinders 2,3, and 4, but my guess is that has something to do with the low compression (hopefully just a stuck ring) in cylinder 1. Would a proper carb sync possibly cure the dormant cylinder?
                Get #1 cyl firing before you start fiddling with carb sync. Make sure you check for correct petcock operation while you're inspecting it. It would be prudent to check valve clearances - no telling when it was last done.
                1981 gs650L

                "We are all born ignorant, but you have to work hard to stay stupid" Ben Franklin

                Comment


                  #9
                  The airbox-to-carb boot on #1 was only partly on and was probably leaking pretty bad. Its starting and running pretty well now, but the idle will hang around 3000 RPM if I'm cruising and pull in the clutch. I've got new boots on both sides of the carbs with new o-rings on intake boots. I've sealed the airbox with weatherstripping and put a new air filter in. I don't have the breather hose connected (PO had pods, so no hose) but I've read that that shouldn't matter and wouldn't cause a hanging idle. Would a proper carb sync possibly help the hanging idle?

                  Comment


                    #10
                    Yes. You need to synch the carbs. However, the sync measures the vacuum on each of the carbs. The vacuum made by the cylinder is effected by the valve clearances. You need to set the valve clearances before syncing or your sync will be off.

                    So, valve clearances first and then sync. This should do wonders for the running condition.

                    Good job and good luck.

                    Chris

                    Comment

                    Working...
                    X