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1979 gs1000l

Discussion in 'Mechanical & Technical' started by winky, Jul 18, 2012.

  1. My buddy just picked up a GS1000L last night for 700.00. The thing cosmetically is flawless, braided brake lines, nice glass packed exhaust, etc. The bike idles well but when you get on the throttle hard it seems like 2 cylinders drop off. There doesnt seem to be any leaks and the previous owner was convinced it is probably the coils.

    Any input would be greatly appreciated. At light throttle the bike is perfectly happy but as soon as you get on it hard it bogs down and 2 cylinders drop off.
  2. RedKat600

    RedKat600 Vintage Screwball Staff Member

    Sounds like carb issues to me....possibly holes in the diaphragms. Pop the tops off the carbs and have a look see. How long did sit/has it sat for? 90% of suspected electrical issues like this are actually carbs....just a heads up.

  3. The guy had taken off the carbs that were previously on it and is running a single carb setup on it instead. They were put on pretty recently and he said suspected it was the carbs before but after replacing them with this big single carb it was still having the issue. So he seemed to have ruled that piece out.
  4. Have you checked the plugs?
    That might give you an idea if some are not firring or running lean ^^^^ bad or sticky slide/s.
    Partly clogged main jet/dirty or fouled carbs.
    Might need more INFO. oops, WILL need more INFO:mrgreen:

    Edit; I didn't see that ^^^^^ last post.

    Start with the basics and narrow it down.
    Have a repair Manual?
    Last edited: Jul 18, 2012
  5. Single carburetor on a gs1000?
    Weird. I just gave a bunch of stuff to a friend in puyallup. I am sure he wouldn't mind selling you a rack of carburetors.
    Let me know and I will put you together with him.
  6. I had an '78 KZ1000 LTD which is advice is pull the spark plugs and have a look. If they are all simular than?? But if 2 are dark, wet, carboned up then you have a firing prob and prob is the coil. Another thing is did you check the valves? Those old bike one has to adjust the valves like an old VW. Also a good thing is do a compression test; you could have ring issues..but then it would blow smoke.?? Glass pack exhaust? Poss. Burnt valves meaning a top end rebuild. Verify the plug wires are going to the right cylinder...might laugh but I have done that. Will idle fine but when you "get on it" there is missfire and should hear backfiring. Water/bad gas? You seen the commercials. Get some "seafoam". Clogged fuel filter/tank valve? Or corrosion in tank. And the list goes on........HAPPY EASTER EGGING!:mrgreen:
    Last edited: Jul 18, 2012
  7. GS check list.. (ignoring the carbs as it's been swapped)

    1. Check your coil voltage. GS's have a long wiring path that runs coil power through the kill switch. Bad connectios along the way are known to cause low voltage at the coils. If it's low do a coil relay mod.. (See this )

    2. Coils.. one should be firing 1 and 4 and the other 2&3

    3. Still have points or has it been upgrades to a Dyna or Martech (sp)? condenser and points in good shape? check the timing and clearance for each set.

    4. Check your valve shim clearances. They tighten up as the seats wear. You'll need a new cover gasket. Go OEM.. the others leak.

    The OE carbs for 79 were VM26s. No diaphragms just slides. They work best with the factory air box setup and stock pipes.. I can't say how it should be tuned for a single carb.

    Lots of great GS tech info here

    Join the GS Resources
    Last edited: Jul 18, 2012
  8. Still has points system, valves were done 2k miles ago, the only thing really still from 1979 on this bike that hasnt been modernized in some way in the past 2-3 years are the coils apparently.

    the 8ft of cabling on a 33 year old coil that he said was reading between 6-7volts i think is what he said last time he tested it. Sounds a bit low to me.

    The guy he bought it from works at Smokey Pt Cycle barn so he seemed to know his stuff. Just helping my buddy narrow things down a bit.
  9. So there are two sets of coils on the bike? or is it just 1 module but 2 connectors? Sorry, im a fuel injected just have a shop fix my bike sort of rider.
  10. RedKat600

    RedKat600 Vintage Screwball Staff Member

    IF the coil voltage is reading at 6-7 volts, that's a wiring issue not a coil issue, and very possibly your problem. Check the grounds where the coils mount, and consider replacing the wires that feed the coils power. A coil relay mod is a simple tool/mod for this that will bypass the factory harness and provide full battery voltage to the coils. They are still switched on by the key too.
  11. 2 sets of coils.. 2 plug wires each.
    One fires cyl 1 and 4.. the other fires 2 and 3..
    Wasted spark system fires every revolution.

    You want 11-12v at the coil.. 6 volts is not good at all..
    as a test try jumping from the battery to the coils and take it for a ride..
    Positive wires on the coils are orange/white stripe. Black wire goes to the 2-3 points White to the 1-4 points.

    Sounds like a coil relay mod is in order.

    All you are doing is using the old coil power line to switch a relay. The relay gives the coils a good 12v feed from the battery.

    What is the battery voltage with the bike running?

    These bikes have a few common electrical issues that are easy to fix.
  12. 2 Sets of coils within the 1 module? Or do we need to buy 2 modules?

    What do you mean try jumping from the battery to the coil, basically just wire it straight to the coil?
  13. RedKat600

    RedKat600 Vintage Screwball Staff Member

    Yes. From your description, the coils are fine. The supply voltage to the coils is in question. Run a wire from the Pos terminal of the battery directly to the orange/white wire lead on the coils. Go for a ride, see if things get better. If they do, you need to do the coil relay mod. If they don't, consider testing/replacing the coils.
  14. I like that idea, we will give that a shot tonight. How difficult of an install is the relay system? I saw a diagram of what it will potentially look like but have any of you guys done it?
  15. RedKat600

    RedKat600 Vintage Screwball Staff Member

    For those of us electronically inclined, once I had access to the required areas it's a 10 minute or less wire job. Really quick and simple.
  16. We decided to check the charge going to the coils and it was sitting at 11.5 volts so we know its getting enough juice to the coils at this point we ordered new coils and are going to install them next week.
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