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Thread: Twin '77 GS550 Projects

  1. #1
    Join Date
    Jun 2013
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    MA
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    866

    Default Twin '77 GS550 Projects

    We've added a few bikes to my household over the past few months. More specifically, we've added three of the same bike. The first was an '81 GS550 that had essentially been restored. This weekend we picked up two 1977 GS550's. One for my other roommate and then I had to get one to match, too. Our other friend also has a '77 GS550 (and two complete parts bikes in our driveway...yup, 6 total) so we have a crew now.

    The first is my roommates. Somebody painted it this dark purple at some point which looks great except the right side cover. It runs but needs to be gone through after being neglected a bit by the PO. They were an MIT grade student and I would think they would have fixed it up a little better. There's JB weld sealing the valve cover gasket as well as repairing a big dent in the stator cover.

    The second (green with pinstripes) is mine and has been sitting since 1981. The PO bought it in 1979 from the original owner. Under an inch of dust is a very clean unmolested bike. The gas in the tank turned to varnish and I believe is what is causing the slides in the carbs to be stuck. Other than that, it turns over with compression and is in pretty good shape all things considering.

    The plan for both is:

    - Carbs (already got kits from cycleorings)
    - Valve adjustments
    - Oil
    - New batteries
    - New front and rear suspension (Sonic + Hagons)
    - SS brake lines up front + new master cylinders
    - Tires
    - Chain + Sprockets
    - Dyna ignition + coils (at least for mine)
    - SPG, coil relay mods
    - General clean up/bathtime

    Should have a couple nice '77 GS550s soon.





    1980/1981 GS450 - GS500 Cylinder + Piston Swap - "De-L'ed", custom seat, CB350 bits, 18" rear, etc.
    1977 GS550
    1977 GS750 - Cross country trip thread

  2. #2
    Join Date
    Feb 2014
    Location
    Netherlands
    Posts
    1,018

    Default

    Both still have the original pipes ? Cool.

    6 bikes ... no shortage of parts !
    What a luxoury to just get the best parts from 4 donor bikes.
    Good plan to sort out the technical stuff first, good luck
    with that. I guess we will see the build thread coming.
    Or 2 threads ?

  3. #3
    Join Date
    Jun 2013
    Location
    MA
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    Default

    I got the #2 bike (green one, mine) running over the weekened. First start in 39 years after a valve adjustment and a full carb clean with new O-Rings and intake O-rings. New OEM air filter as well. Idles well and it was nice to see decades worth of grime smoking up off of the engine (even after I had given it a good clean). A couple of the slides were stuck in the carb bodies which I deduced was the needle stuck seated in varnish (they had 39 year old gas gumming everything up). Charging system and electrical everything works well but I'm also going to clean that up eventually (SPG, SH775, etc.)

    Also did a valve job and an oil change on bike #1 with a carb clean to come.







    The petcock on #2 bike was totally clogged so I took it apart and am piecing parts from another OEM petcock I have to make one good one. In the meantime, I threw in a couple handfulls of pennys and have been swishing them around to clean out some light surface rust and varnish which has been working extremely well. I drew up a quick petcock plug that I'm currently 3D printing (a couple hours left) and am hopefully going to flush the the tank out tonight, then fill with vinegar for a few days before another flush before installing the rebuild petcock and filling with gas.



    I'm ordering sonic springs today for both (as well as the other '81 GS550 my other roommate has) as well as some fork oil and seals. The front suspension on my #2 bike is literally useless to the point that I would feel unsafe riding it around. Also ordering some brake line parts from Earls.
    Last edited by sam000lee; 08-24-2020 at 10:33 AM.
    1980/1981 GS450 - GS500 Cylinder + Piston Swap - "De-L'ed", custom seat, CB350 bits, 18" rear, etc.
    1977 GS550
    1977 GS750 - Cross country trip thread

  4. #4
    Join Date
    Jun 2013
    Location
    MA
    Posts
    866

    Default

    I've put together one good petcock from three that I had lying around:



    However, the filter that went with this body was slightly different than the two from the other petcocks. They had a small tab that you can see in the picture that I believe I can just shave off. Has anybody done this? Looking at the parts fiche, you can buy a replacement gasket to the tank (ordering that today from the dealership), but not the filer separately. You can see the difference in this picture:

    [url=https://flic.kr/p/2jAcZQZ]

    My tank is full of vinegar as of last night. My 3D printed plug is working like a charm after using a piece of rubber as a gasket. I checked the inside this morning and am really pleased with how it's looking inside and out.

    1980/1981 GS450 - GS500 Cylinder + Piston Swap - "De-L'ed", custom seat, CB350 bits, 18" rear, etc.
    1977 GS550
    1977 GS750 - Cross country trip thread

  5. #5
    Join Date
    Jun 2013
    Location
    MA
    Posts
    866

    Default

    Got some OEM replacement gaskets for the petcock for the #2 bike and flushed the vinegar in the tank and filled it up. The inside is spotless now which is really satisfying. I also bled the brake line which actually works great now, despite the original lines (swapping them out for both bikes soon anyway).

    Installed Sonic Springs into both bikes.

    For the #1 bike, we rebuilt the carbs with new O-Rings and it starts up and runs great.

    I've been running errands on my #2 bike for the past 5 days and it runs fantastically, especially after putting in a new set of plugs. It's so quiet on the highway and I ended up pushing it up to 100mph. The bike took it no problem and had more to go so I'm quite please with that. My DRZ400 was stolen out of the driveway on Friday so with this up and running I still have the same number of rideable bikes...

    I've been cleaning up little bits and pieces with an old toothbrush/rag/tin foil and it's cleaning up really nice as well. I desperately need to replace the tires on it so am ordering them in the next couple of days. I'm looking for a not-super-modern looking tire that won't sacrifice performance. On my other bikes I've used the Dunlop K70s (look cool), IRC GS-11's (also look cool) and Shinko 712's (cheap and perform decent), so hoping for something in between. Looking for suggestions if you have 'em.

    Next up is replacing the brake lines.



    Last edited by sam000lee; 09-07-2020 at 09:55 AM.
    1980/1981 GS450 - GS500 Cylinder + Piston Swap - "De-L'ed", custom seat, CB350 bits, 18" rear, etc.
    1977 GS550
    1977 GS750 - Cross country trip thread

  6. #6
    Join Date
    Jun 2013
    Location
    MA
    Posts
    866

    Default

    I got my bike to a really solid place over the past week after installing 340mm Hagons, new IRC GS-11 tires and an extra flat seat I had lying around. I'm going to re-upholster the seat over the winter so ignore the rips.

    One thing is that I'm having an issue with the front break. It had been seizing up after I bled all the old fluid out of it. I figured one of the caliper seals was bad so I replaced it with another caliper that was working fine. Took it out for a couple of miles and it seized going ~40mph. I thought something else was wrong but after clutching in to a stop, the front brake was smoking and I couldn't roll the bike. I'm a little puzzled by this since by replacing the caliper, I believe I've eliminated that as the issue. Could this be caused by the MC? I'm not sure how that would be possible but want to consider all possibilities.

    Here's some pictures of the bike how it sits now. It's looking pretty











    1980/1981 GS450 - GS500 Cylinder + Piston Swap - "De-L'ed", custom seat, CB350 bits, 18" rear, etc.
    1977 GS550
    1977 GS750 - Cross country trip thread

  7. #7
    Join Date
    Sep 2012
    Location
    Ireland
    Posts
    4,364

    Default

    Brake seizing on is a classic symptom of the tiny return hole in the master cylinder being blocked.
    ---- Dave
    79 GS850N - Might be a trike soon.
    80 GS850T Single HIF38 S.U. SH775, Tow bar, Pantera II. Gnarly workhorse & daily driver.
    79 XS650SE - Pragmatic Ratter - goes better than a manky old twin should.
    92 XJ900F - Fairly Stock, for now.

    Only a dog knows why a motorcyclist sticks his head out of a car window

  8. #8
    Join Date
    Jun 2013
    Location
    MA
    Posts
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    Default

    I ended up replacing the MC with one from a parts bike after trying to clean/blow out the original. Front brake is good to go now although I plan to replace the line at some point with an SS from earls. Now for the next problem.

    I've been ignoring what I've suspected was a fuel delivery problem. The #3 cylinder takes longer to warm up than the others when tapping the pipe with my fingers on a cold start. Best guess was a stuck float and I wasn't far off. I took the carbs off last night and pulled the float bowl for the #3 and #4 cylinders to compare them. I also took each of the floats out to compare the float needles to make sure they were in good shape. Reassembled them only to find that now #3 AND #4 pipes were cold on start. After pulling the drain screws, they weren't getting gas. Pulled the carbs again and ALL the float bowls. Stupidly I had installed them both upside down hence the no gas.

    Okay so for my current issue:

    When I took the carbs off the second time, I pulled all four float bowls (to find that #3 and #4 were upside down) and noticed that the #3 float was set at a higher height than the other three. #1, #2 and #4 were all set at ~22mm with #3 at ~25/26mm. They were visually different. After a quick check of the manual, I re-adjusted #1, #2 and #4 to 26mm. Now upon installation, the bike starts up right away, is getting fuel to all four carbs, idles smoothly, but now has a hanging idle. There are no leaks, I've done my due diligence there.

    So I have two theories as to what HAD been happening with the #3 carb:

    1. Float was originally installed upside down so the bowls didn't have enough fuel.
    2. Float height was set too high at 26mm. Higher float height corresponds to a lower level of fuel in the bowl so at idle the pilot jet wasn't able to suck up enough gas.


    That doesn't super matter, just thought I'd state my two hypothesis.

    My theory as to what is currently happening:

    After raising the float height to 26mm, all four carbs are starved of fuel at idle and running lean, hence the hanging idle. For whatever reason, the float height should be set back down to 22mm for all of them.

    Hoping to get some input whether or not this makes sense for what to do next. I don't mind taking the carbs off, but the GS550 carbs are of the more difficult/annoying to get off. It takes about an hour to get them off, tinker and put them back on and I have limited non-work daylight hours. Preferably I only have to do this one more time.
    1980/1981 GS450 - GS500 Cylinder + Piston Swap - "De-L'ed", custom seat, CB350 bits, 18" rear, etc.
    1977 GS550
    1977 GS750 - Cross country trip thread

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