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78 GS550, Another one with issues

  • Thread starter Thread starter shmoody
  • Start date Start date
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shmoody

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Hey. Thanks for such a great site, has been really helpful so far.

1978 GS550 10000 Miles, Bought it for 400.00 and Have already made my money back from gas savings, but now I got Issues

Well I've cleaned the carbs serval times, sealed the tank, changed the oil, replaced intake o-rings, and plugs...

Has been running extremly good, yet one day started to notice it running a little weak, and rough.

At stop lights the bike idles really high, put it in first and let off the clutch a little, then its fine, put the clutch back in, idles perfect. Next stop light I have to do the same thing.

Also the bike has intermettiant (sp) times will backfire, and run really bad upon acceleration, won't almost dies, then catches again.

Changed plugs, cleaned carbs, changed oil... plugs where black sooty, (rich). When cleaning the carbs, I set the bottom screw, can't find specs, to one turn out... the side screws to 1.25 out.

I don't see any vaccum leaks (carb spray and the little hose at every opening). pitcock, seems ok I think, doesn't matter any position.

I don't know whats going on, I work on newer cars for a livin'. I sometimes don't understand these carbs, but am getting there...

Any Ideas will be Helpful,
Thanks in Advance
Shmood
 
Sounds like an intake leak. The carb spray technique is unreliable and does not detect smaller leaks. Inconsistant idle could also be caused by poor sync so that should be checked as well.

Oh, and your air screws should be in the range of 1.75 turns out from lightly seated.

Have fun.
 
I agree with Ed. Redo the air mixture screws by the highest idle technique method. Do a carb synch with motor warmed up. The high idle speed certainly indicates an air leak of some kind. Even air screw adjustment that is way off and letting too much air in at idle will cause a high idle. Check the seal with carbs to head and carbs to airbox as well. I had a bad air leak once and found that the carbs had almost completely pulled out of the rubber boots that connect it to the head. Just pull the tank and check over everything.
 
Have you replaced the points and condensors on your ignition?

Cheap and easy to do. I had all sorts of weird stuff going on that seemed like carbs, air leaks etc. It was a bad point that was causing hesitation, backfiring, etc.

Another easy mod that is a must do is the coil relay mod. I have read that low voltage at the coils cause similar problems that WONT be helped by perfectly cleaned carbs (although this is very good and should be done:)).

Good luck!

Rick
 
Well,

I Was starting it today. Didn't start, no crank, nothing, had power (Lights, etc...) Flipped the kill switch several times, and then like butter, running ok too, high idle. Dropped the choke, adjusted the idle screw...

Able to run home, only backfiring a little bit, but this time, it almost seemed like it died, but grabed right away...

Now I'm really leading towards coil mod, but I have a quick question, and I'll probably find a wire diagram before someone answers this but, the kill switch cuts off power to the starter and coils, Correct?, Therefore just cleaning the switch it would fix it?

Anyways, I believe carb spray will even find leaks that would cause this issue, large enough the cause high idle, large enough to be changed by carb spray.

So, knowing that all four plugs are showing signs of richness, and the kill switch (right?) give juice to what ever the coils get there juice, if juice is low, cylinders would run rich, cylinders getting the wrong amount of spark for the amount of feul. When it backfires, its a build up of gas in the intake...

I know, I know I'm really reaching here, but I think I know what I'm doing, I hope... When all else fails try anything that you haven't...

Thanks for the Ideas will keep it posted
 
shmoody said:
At stop lights the bike idles really high, put it in first and let off the clutch a little, then its fine, put the clutch back in, idles perfect. Next stop light I have to do the same thing.
Click to expand...

This is a symptom of out-of-sync carbs.

There's other possible problems, but this will be cured with a carb sync.
 
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