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'77 GS550 hates me

  • Thread starter Thread starter somedeadguy
  • Start date Start date
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somedeadguy

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I apologize if this scenario has been dealt with, I spent a couple of days using the search tool, but couldn't find anything that worked.

I inherited a GS550 from my father in law who had it sitting in his backyard for fifteen years, bowls full of gas, and everything. After a new battery and some starting fluid, it started right up, and made it home at 75+ mph. It never charged, but it wasn't a big deal because a full battery lasted a week without having to kick start it. Everything is stock, 4-2 exhaust, plain old airbox, and everything.

It sat for a month this winter (I drained the bowls) and when I got it going it didn't run right. It was backfiring, and couldn't go above 45mph and sort of sputtered and surged. So I looked on this Forum, and everything I found said "clean the carbs". Backfiring to me means a timing problem, but everything I read here said carbs, so what the hell. I figured it was high time anyways, so I dropped $150 just for the rubber boots between the carbs and heads, got new o-rings for the intake, o-rings for all the screws, and a little o-ring kit for the main jet and connecting things between carbs. I dipped and blew out everything, and surprisingly the carb were pretty clean after sitting for 15 years. I got everything perfect according to the book, or some things according to this forum that weren't in the book. I synched em great, and put the carbs back on.
Same thing. So, then I figured I would go with my gut instinct, and play with the timing. I tried the method by setting the widest gap to 14 thousandths, and then adjusting them to the timing mark. It fired right up! No backfiring at all! Idles strong too! But it won't rev!

I think that I never had a carb problem in the first place, it was just the points! But too late now, I've already screwed up the carbs, and now I'm stuck. Everything is right on the carbs, and clean. Whether I try to richen it or lean it out, it still won't rev. If I give it any throttle it just gets loud and throaty, but the RPM doesn't increase or decrease, it just gets loud. I took the carbs off again, cleaned them, resyched them even though there wasn't much of a change, no difference. I used a timing light and it's firing way before TDC, but I read on here that that is normal. SO I don't know what else the problem could be. I have no air leaks, no fuel leaks or blockages, clean filter, good gas, and everything. Could it be that this bike just hates me?
 
I haven't done a compression test yet. The valve clearances are good, it seems like the timing is a little funny, but if I were to move a tooth in any direction I think it would just throw it off more. I will do a compression test soon. Is it possible for the compression to go bad just from sitting? If my compression is bad that means I need new rings right?
 
The valve clearances are good, it seems like the timing is a little funny, but if I were to move a tooth in any direction I think it would just throw it off more.

It doesn't make sense to change crank/cam timing, since it ran fine when you drove it home. Try step-by-step diagnosis from the beginning, even if you repeat some things you've done before. And listen to the elders on this site...they are really knowledgeable!
 
The idle control screw

The idle control screw

since you have had the carbs off... turn the idle screw that rides btwn carbs 3 & 4 to the right about half way, lift the choke lever on the side of #1 and try staring it again... you may have changed the setting of this control when you cleaned the carbs.... also make sure the airbox is set back in place correctly... it is critical that the air flow be properly restricted in order to run correctly.. on another note::

the battery not charging maybe a bad rectifier/regulator and/or stator. needs to be looked at sometime in the near future....

btw the 77-79 550's are nearly all electrically the same and carburated identical... just 78-9 they added the e models..

Joe
 
Clened carbs again...

Clened carbs again...

Cleaned the carbs again and they are pristine. The throttle slide is maybe a half a milimeter from the very bottom of the venturi when closed and without the idle screw touching. It is a little more than half a mm above the top when open.

Did a compression test and I got 106 (give or take) on all the cyls. 1 and 4 were a little less than 106 and 2 and three were a little more. That's pretty good for a 30 year old engine!! Certainly good enough to run, right???

The airbox appears to be mounted correctly, I put a piece of rubber all around the joint just in case. As I said before all of the rubber is new in the carb.

Fired it up again, and it started right up! In fact with the choke on it went up to 3000+ rpm after about thirty seconds. I figured it was running a little rich or something so I pulled the choke off and it died.

After playing with it, I have the same problems. It doesn't die right away with throttle, it just gets really throaty sounding, and the rpms slowly drop. I couldn't get it to rev past 3500. It won't run at all without choke, and it runs poorly at about 500 rpm with half choke.

I just can't figure it out.

I also check the cam timing (just by looking through the spark plug hole with a flash light) and it seems great. It's really tight, the very instant the exhaust stroke starts the valve opens, and then the very second the piston hits tdc the fuel valve opens. I heard that the valve timing was supposed to be really retarded, so I'm not sure if this is right, but from a basic standpoint I think it should work.

The points are hitting really advanced, but it's not backfiring anymore, so it would seem like that isn't a problem.

The fuel is flowing great, got a new filter, the petcock is clean and works good. There are no vacuum leaks that I can tell. I don't know what's left.

Oh, the coils are working, I've got a nice spark, and the plugs are dry but brown. Are you sure it's not a personal thing between the bike and me?? I remember I made fun of Suzuki's once when I was a kid. I said that a Samarai was a piece of crap and I could out tow it with a Huffy bike. I think it hates me. I'm getting really close to mounting an old shovel head v twin on it out of spite.
 
One more thing

One more thing

I did see two or three sparks or arcs through the points that serve the 1st and 4th cylinders, but then it stopped. I'm aware that this can mean that my condensers are starting to go out. Could that have anything to do with bike running bad? I'm not exactly certain what condensers do, I thought they just let the volts build up untill they are discharged or something along those lines. Also, just for the hell of it I was wondering what the little slot on the left side of the engine is for. It's cover by a little cap about 4 or five inches from the stator towards the rear of the bike.

Thanks everyone for helping, sorry for being so apathetic, I just have never understood why these bikes are made so complex.
 
The rubber connections to the airbox can be a killer too. Check them and make sure the clamps are on right and tight. Sounds like an air problem.
 
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