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Runs rough after rebuild

  • Thread starter Thread starter porkpie1492
  • Start date Start date
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porkpie1492

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Hey guys, I have been working on an 82 GS650G, trying to get it to run. Some of these things I would probably figure out through trial and error anyway, but I am on a bit of a time limit trying to get my bike ready to take to school. Anyway, I recently cleaned and rebuilt my carbs, new o-rings, new intake boots and o-rings, etc. Everything seemed to go well, and after reassembly the bike started and idled nicely. Upon a test ride, I discovered that the throttle doesn't respond nearly as quickly as it should in gears above first, and it loses considerable power when going up the slightest incline. The RPMs drop, and I have to quickly downshift to keep from stalling. A couple of things that I have since considered:
1. I didn't understand what I was supposed to bend when setting my float height. Instead of bending the little tab, I bent the "wings" up to set the height. The height is correct, but instead of having a slightly drooped profile, the wings curve up the slightest bit.
2. I didn't check the fuel level with the hose and caliper. There doesn't seem to be any leaking, but could this affect my running performance adversely?
3. I bench tuned the carbs, but am waiting for the carbtune to show up. This I'm sure will improve things, but will it affect my power?

I guess my questions would be, should I go back and try to rebend the floats, or could it be necessary to replace them? Would not testing fuel height with the hose affect performance in this way?
I also considered ignition timing being off, but want to eliminate the carbs as a potential culprit first. Sorry about the long-winded post. Much thanks to Ed Ness and his carb guide.
 
I would bend the float wings back straight and adjust by bending the small tabs. That would be the best option. Bench syncing the carbs should be about 90%. You're okay. Carbtune if you would like. How far in are your fuel/air screws? You may be running too lean.
 
I followed the generic instructions in the guide. Screwed them in til they bottomed out, then backed them out 2.5 turns. It said to fine tune them later, but I haven't done that. Would a lean fuel mixture have such a dramatic effect on power?
 
Hi,

Is your airbox and air intake system properly sealed up? No leaks?


Thank you for your indulgence,

BassCliff
 
Make sure "choke" is fully disengaged when off at carbs ( push bar back in if need be). Mine doesn't like "choke" on once you start loading engine by accelerating, going up hill, etc.
If you rebend the float tabs, spot check the vacuum pistons/diaphragms to make sure they aren't sticking
 
I haven't sealed my air intake because it all seemed to be in good condition. Is there a good way to test if my air boots are leaking? There is some fore and aft motion, but it seems like this is necessary in order to remove the carbs. I'd rather not replace them unless I have to. I suppose the next step is to go through the air system.
Tom203 - do you mean make sure the choke bar isn't sticking?
 
It's probably best to rebend floats and set height the correct way. When you activate "choke" lever, the bar that connects all 4 choke plungers moves to left- when you turn off choke, the bar must move all the way back to its "off" spot- push on it to ensure it's fully off.
The airbox should fit tightly on carbs mouths, the filter element should be in place and cover on, and the filter box should fit tightly on airbox . Any leaks will eventually cause stumbling as throttle is advance- but so wouldn't a wrong fuel level in bowls.
 
I am going to do this tomorrow. I am also correcting my tappet clearances. I am going to re-examine my air filter - the manual says to thoroughly soak with oil, then wring out and install. I read on another thread that a light spraying of oil will suffice. I am concerned that my filter is too wet, and thus not allowing sufficient airflow. I will let you know what happens.
 
So - I discovered some fairly dramatic air leaks. I am removing my carbs AGAIN, and replacing the air boots on the air box. Also, the slide connection point between the airbox and the filter box is leaking. Any ideas on how to seal that without compromising its ability to slide?
On a separate note, I am concerned that my slides are not returning to their bottom position as well as they should. They return smoothly, but slowly, and after a moments hesitation. There doesn't seem to be any wear within the bore. Could I just rub some engine oil on the slides to loosen them up? Could this be contributing to my hanging idle and lack of power on hills?
I might just make sure the bench sync is solid, and call it good, then balance the air screws to one another. If all this doesn't work, then I don't know where else to turn for my power related problems, other than having bunged something up in the process of the carb rebuild.
Oh yea, the floats are re-bent, and the height adjusted again.
 
There should be a "hose" clamp securing the oval connection between the filter box and airbox. The two parts should mate snugly even without the clamp.
The slides might hesitate a bit after being raised before dropping down- I figure engine vibrations help out here. I wouldn't use engine oil- too sticky, try silicone spray (not WD40). Obviously, the slide bore must be free of dirt! remember that as throttle plates open, increasing vacuum is applied to top of vacuum pistons to make them lift.
The air filter element just needs a light oil on it
 
Thought I would just throw in:

The mixture screws on the top of the carb and syncing the carbs, these only affect the engine at idle. So if it idles fine and the transition from idle to mid-range is okay, these are good. (Or good enough.) It sounds like your problems are caused by a lean mixture and you're already on the case with the air leaks.
 
The oval connection has the clamp, but it leaks anyway. I tested my air leaks by spraying starter fluid in all the suspect ares, and seeing if the idle reacted. I'm trying to think of a way to seal this part so that it can still move. My thoughts so far - I have some thick-ish silicone(?) tape that might work, or use one of those plumbing hose clamps. I can crank the screw on the OEM clamp all the way down, but it isn't enough. The plumbing clamp would advance past that point and give a tighter fit. I could also wrap the shaft of the oval fitting with that white plumbers sealant tape.
The other leaks come from the inner two airbox boots. The rubber on the boots is still soft and malleable, but when the outside boots are seated nicely, the inner ones won't push forward far enough to grip the lip of the carb. It looks like the surface of the airbox where the boots fit is a little concave. I'm thinking of using a hairdryer and bracing it to form a more convex shape that would push the inner boots forward farther in relation to the outer ones. Any thoughts?
Silicone spray? Isn't silicone an adhesive?
 
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