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Thread: VM26SS Troubles

  1. #1
    Join Date
    Apr 2020
    Location
    Tell City Indiana
    Posts
    10

    Default VM26SS Troubles

    I recently replaced the float bowl gaskets and adjusted the float height on my 78' GS750 because the bowls were leaking profusely, following this the bike ran lean so I took the carburetors back off to reset the float heights. After I did this the bike did not want to stay running when cold, It would rev to about 3000 rpm and then immediately drop down and stall no matter what I did until it was warmed up. I replaced the intake O-rings that seal the carburetor boots to the head and it runs good now except I now have to give it a little throttle until it warms up and the plugs are still white. I reset the float heights so I don't know why it would still be running lean and better yet it runs fine, could it be that I still don't have the floats set right? Or is it something else, it never ran lean before so I'm struggling. Thanks everyone, this site and everyone's wisdom is much appreciated.

  2. #2
    Join Date
    May 2009
    Location
    Norman, Oklahoma
    Posts
    24,927

    Default

    Turn the air screws on the side of the venturis all thee way in then back out 1 1/4 turns. Turning screws IN makes the cylinder RICHER. OUT makes it LEAN. Also the big knob between carbs 2 and 3 is the idle adjusment
    MY BIKES..1977 GS 750 B, 1978 GS 1000 C (X2)
    1978 GS 1000 E, 1979 GS 1000 S, 1973 Yamaha TX 750, 1977 Kawasaki KZ 650B1, 1975 Honda GL1000 Goldwing, 1983 CB 650SC Nighthawk, 1972 Honda CB 350K4, 74 Honda CB550

    NEVER SNEAK UP ON A SLEEPING DOG..NOT EVEN YOUR OWN.


    I would rather trust my bike to a "QUACK" that KNOWS how to fix it rather than a book worm that THINKS HE KNOWS how to fix it.

  3. #3
    Join Date
    Apr 2020
    Location
    Tell City Indiana
    Posts
    10

    Default

    ok, I wasn't sure if I should mess with the air screws or not because I know how finicky it can be to get these carburetors in sync. Ill mark where they are now just in case that doesnt help so I can get back to the factory settings. Thanks!

  4. #4
    Join Date
    May 2009
    Location
    Norman, Oklahoma
    Posts
    24,927

    Default

    air screws have nothing to do with syncing carbs. look here for the EARLY 8 VALVE service manual so yu know what youre doing. PS... Factory set them lean to pass EPA back in the day


    http://members.dslextreme.com/users/bikecliff/
    MY BIKES..1977 GS 750 B, 1978 GS 1000 C (X2)
    1978 GS 1000 E, 1979 GS 1000 S, 1973 Yamaha TX 750, 1977 Kawasaki KZ 650B1, 1975 Honda GL1000 Goldwing, 1983 CB 650SC Nighthawk, 1972 Honda CB 350K4, 74 Honda CB550

    NEVER SNEAK UP ON A SLEEPING DOG..NOT EVEN YOUR OWN.


    I would rather trust my bike to a "QUACK" that KNOWS how to fix it rather than a book worm that THINKS HE KNOWS how to fix it.

  5. #5
    Join Date
    Apr 2020
    Location
    Tell City Indiana
    Posts
    10

    Default

    I put new plugs in and took it for a ride and its running good and the plugs read good, however would anyone happen to know why I have to give it throttle until its warm now, could it be another vacuum leak?

  6. #6
    Join Date
    Mar 2005
    Location
    West Slope, OR
    Posts
    11,891

    Default

    The choke doesn't work?
    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

  7. #7
    Join Date
    Apr 2020
    Location
    Tell City Indiana
    Posts
    10

    Default

    The choke works, but after it starts up the revs slowly start dropping and it dies unless you give it a little throttle. I'm going to put new O-rings in the carburetors and run new fuel and vacuum lines and see if that takes care of it.

  8. #8
    Join Date
    Mar 2005
    Location
    West Slope, OR
    Posts
    11,891

    Default

    Have you adjusted the valves?

    Also, you say it ran good before you worked on it? Tell us exactly what you did
    Last edited by Big T; 05-07-2021 at 12:37 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

  9. #9
    Join Date
    Apr 2020
    Location
    Tell City Indiana
    Posts
    10

    Default

    Ok so ill start from the beginning. My GS750 was running good but the carburetor float bowl gaskets were really old and leaking like a siv, I put new float bowl gaskets in it and mildly adjusted the float height to be a little lower based on my manual's specifications. After this the leaks were fixed and the bike ran well however I checked the plugs and they we're white. Because the bike ran perfectly fine before this it was safe to assume it was a result of my float adjustment. I took my carbs back off and adjusted the floats to where they were originally and this fixed my problem however a new problem arose, when cold the bike would immediately start choking down and die, but once warmed up would start and run good, just setting it out in the sun on a warm day would warm it up enough for it to start good. I reasoned this was a vacuum leak somewhere so my first bet was to change the O-rings between the head and the carburetor boots, I ordered some from cycle O-rings along with the stainless allen head screws for the boots and replaced the old ones, the old ones were probably originally as they were very brittle and one had a gaping crack. This helped significantly with starting but it now acts as if its receiving to much fuel when cold starting with the choke on. When I start it, it revs to about 3,000 rpm like it used to when cold starting with the choke but then starts to bog unless I hold the throttle open a little bit. I'm thinking it could be another vacuum leak so I'm thinking I should put new O-rings in the carbs and run all new hoses for good measure as the ones on it are fairly old. My bike is completely stock and I've had it 3 years with no troubles, all I've done to it so far is regular maintenance like replacing the weak clutch springs because the clutch was slipping, updating the regulator rectifier with a ricks motorsports one (I know sh775 is recommended but I liked the simplicity of ricks option), new gaskets, a new paint job, etc. I haven't adjusted the valves though, the bike is sitting at just over 50,000 miles so I'm sure thats probably due but I don't have any noise coming from the valve train and it didn't have any trouble starting before so I don't believe valve adjustment is my problem but I have far less experience than many of you. Thanks for all of your help, this community is really nice.

  10. #10
    Join Date
    Mar 2005
    Location
    West Slope, OR
    Posts
    11,891

    Default

    No noise from the valve train is a bad thing
    After 3 years, you're overdue
    Get yourself a valve cover gasket before you start
    It does sound like you have a carb issue. You need to check the pilot air and fuel settings, and maybe clean the carbs
    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

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