New poster, been lurking for quite a while though, as I picked up a 2001 GS500 with 12K miles that had been sitting for a long time, and have been reading up on maintenance, and searching for solutions to my problems.
I'll try to do this somewhat chronologically:
-Picked up the bike, it had been out of commission for about 4 years with the carbs removed to be rebuilt, but it never happened. Before that, the bike would have a hard time running without the choke, and idle would go up and down, usually running around 3K RPM. While it was having this problem, the prior owner also checked and adjusted the valves.
-Drained the gas tank (no rust) and refilled it, and did round one of the carb cleaning. Jetting is stock.
-Couldn't get it to start.
-Checked the plugs(clean and in good shape), and used my timing light to make sure they were actually getting a signal. Also, pulled one and checked for spark visibly.
-Another round of cleaning. Had to get two different style carb kits as the original ones I bought advertised as for 2001-2002 carbs contained the wrong float bowl gaskets. Replaced some O-rings on the tubes the main jet screws into. Also replaced the float valve (and the cylinder it sits in) for one of the carbs, as it was pretty corroded, and the o ring on it was bad.
-Couldn't get it to start.
-Pulled the air cleaner box, and sprayed the carbs with starting fluid.
-Engine would fire up for a few seconds then die.
-Noticed my fresh gas was pretty dark. Figured out that the new gas was dissolving the old, varnished gas that had dried out some and coated the inside of the tank. From here on out, any testing I did was with pouring good fuel straight into a fuel line directly to the carbs. I'll clean the tank once I figure all this idle issue out.
-Cleaned the carbs again in case the bad gas gummed anything up.
-Friend (and former owner) helped me get it started on starting fluid, and was able to keep it running by manipulating the choke and the throttle. Was back to having the 3K roaming idle, and only running on choke. Closing the choke killed the engine, and it seemed like it was running lean.
-A few days later, went to see if I could figure anything out, and went to fire up the bike again. Could only get it to start on starting fluid, and then it would die fairly quickly.
-Pulled the carbs, and checked the idle mixture screws (didn't think of this sooner, since I figured they'd have been properly adjusted before). Turns out one of them was only 1/2 turn out, and the other was a smidge under 1 turn out. Set them both to just a bit over 2 turns out.
-At the same time, pulled the cam cover, and checked valve clearance. All seems in spec, except the left exhaust valve may be a bit loose, but not by much.
-Was able to start the bike on starting fluid, and it ran a bit longer, but still died. Revved up pretty high before dying, could keep it running for a few more seconds by adjusting throttle position. I had been planning on using my propane torch (not lit, obviously) to check for leaks around the intake boots, but couldn't keep the bike running long or steady enough to attempt it.
Sorry for the novel, but wanted to make sure I'd covered everything I'd done to the engine before asking advice on what to do next. It seems like the bike is just running way too lean as soon as the choke is shut, so I'm assuming its a air/fuel mixture problem of some sort. I may not have time to look at it in the next week or so, so now seems to be a good time to see if the next course of action seems right:
1. Pull the intake boots, and visually inspect them for cracks or bad O-rings.
2. Remove the idle mixture screws, and check for bad O-rings (although I'd think this would lead to a rich condition)
3. ??? I have no idea what else to do at this point. Also, beginning to wonder if the phrase "90% of carb problems are electrical problems" is the issue at hand. But, since I'm getting spark, I just don't know.
Its also not helping that it seems like the carbs on a 2001 are a hybrid of the earlier and later carbs, and I'm having trouble getting accurate information and parts (see the rebuild kit issue above).
Any advice would be highly appreciated.
Not sure about this but it sounds a bit like somebody made a hybrid out of an old 2 jet carb and a new 3 jet carb? Is that even possible? And if it is are the float bowls the same size on both carbs? Sort of sounds like a float problem maybe?
Yes it sounds to me like it might be your float height lever too. It's seams like its a lean condition to me too. Are you running the fuel tap on prime? Are you sure fuel is getting to the carbs?
Here is something you can try. Put the bike on the center stand. Turn the tap to prime so the carb bowls fill, then turn the tap to the "on" position, this will stop fuel entering the carbs. Disconnect the fuel line at the carbs, if you don't do this the fuel in the line will drain out of the first bowl you drain and the reading wont be accurate. Put a small vessel (i use a spray paint can lid) under the carb bowl drain spout thingy. Then drain the carbs into the vessel and see how much fuel comes out of each bowl. This will give you an idea of how much fuel is in each bowl. I'm not sure how much exactly should come out but it should be around 20ml, probably more. If one is way less, then there is your trouble. Or of course use the clear tube method too.
Or just ignore all my :bs: and continue on.
Good luck with it, im sure you will get it sorted.
The carbs are original, three circuits, and float bowls held on by 4 screws, but plastic caps on top. They have the little o-ring, but no opening for it.
I have not mucked with the float levels at all yet, as I haven't found anything telling me what level the floats should be at to start opening the valves. The Clymer manual, despite saying it goes through 2002, seems to only have info for the 89-2000 carbs.
Dont worry about a magic number to set float height, just find out where it is now. Get some clear fuel line, hook it to the carb drain and open the screw. Bend the tube up the side of the carb, and turn fuel valve to prime. The fuel will rise to the height it sits in the bowl. It should be lower than the top of the float bowl, but not far. Float height is important for fine tuning delivery, but I have found that a motor will run on a wide range of float heights, its just not at ideal mixture. The fuel must be at a certain level to take advantage of the pressure differential created by the motors vacuum. Too low, and its hard or impossible for the vacuum to pull it up the jet and into the intake, too high and its too easy to pull the fuel in, meaning more fuel is pulled than is necessary, creating rich mixture.
Just wanted to add a quick note here, in case anyone has a similar issue in the future. Did another pass of cleaning the carbs, adjusted the idle mixture out 3 turns, but what probably did the trick was something blindingly obvious. The idle speed was set too high. I've never worked on a multi-carb bike before, and since the choke setup seemed a little odd, I had just assumed the throttle plates were supposed to be as open as they were. I adjusted it way down, until they were nearly closed.
The bike now idles at 1500 RPM once the choke is closed. When starting it on full choke, the revs want to run away a bit, and it seems like they'll go between 4-6K RPM, before I panic and try to close the choke a bit. There is an occasional ticking noise, possible from the right cylinder, and maybe a slight backfire on occasion, not entirely sure.
So, still needs a little bit of tuning work to be ideal, but at least I can get it running on its own without the choke. Lesson learned is that sometimes it is so obvious, you'd think someone else would have already figured it out.