Did some carb maintenance, now can only start with throttle

[Rahzin]

Hey guys, I'm a bit new here, so bear with me. I bought an '04 GS500F in December which had sat for 5 years or so. Didn't run at the time, but I got it running and have been commuting on it every day since April. For context, the carbs went through an ultrasonic cleaner while I was getting it running. In the last month or so, it's been running more poorly and always does when I come to a stop unless I keep on the throttle for a bit. Today, I decided to set the float height to factory spec since the last time I touched them, it was kind of guesswork. While I was in there, I ran the float bowls and jets through my ultrasonic cleaner again in case there was se junk of a float or something. Everything looked great after that, so I reassembled the carb.

Another thing I had seen mentioned was that idle troubles can be caused by poorly set mixture screws from the factory, so I drilled out the caps and found that the two screws were set quite differently. I set them both to 2.5 turns out as I've seen recommended, and then also moved the carb sync screw such that both throttle plates appear to be in the exact same position with the exact same amount of gap to the carb walls. Seemed to me like getting both cylinders running equally could improve idle. However, I get everything out back together and the choke seems to not even do anything anymore. It used to start right up and go up to 3-4K rpm with choke on, and now it won't even start unless I give it some throttle, regardless of choke setting, and dies if I let go of the throttle. I tried moving the idle set screw around to open the throttle plates a bit and maybe give it some air, but that didn't really help. And as far as I understand, it shouldn't need that with the choke on. I tried tearing it all back apart, checking everything, blowing things out with compressed air. It all looks good to me, but it just will not run anymore. I'm at a bit of a loss! Any suggestions?

If any of you are in the Seattle area and want to come by to help me diagnose, I would pay you in beer or whatever else.

Edit: I should note that I set the float height by measuring 13mm +/-1 between the bottom of the float and the gasket surface of the carb. I don't have any clear tubing to verify that the fuel level is actually there, but since that is the spec adjusent point, I'm assuming it should be right...

[Rahzin]

Update: I moved the float height up to more like 9-10mm, and now it seems to be running. Weird because that is way out of spec, but whatever I guess. Haven't gone on a ride yet, but it idled at 4k with the choke on and then dropped down to about 1400rpm once warmed up. Although it did die the first time I turned off the choke and let the rpms drop. Anyway, tomorrow I'll go on a ride and report back.

[mr72]

I'd suspect either some error in setting float height or sticking float needles. Maybe corrosion or clogging in the float needle seat. I think you are likely to be tearing the carbs down again so this time, replace the float needles and seats and o rings while you are in there.

If you turned the idle mixture needles after they sat for over a decade then the o rings are probably leaking. If you haven't done it already, do a complete replacement of all o rings. Of course you can follow the procedure on my blog to get it mostly sorted. Odds are your idle mixture is way off, probably very lean causing it to not idle. You need bigger pilot jets. And probably leaking intake boot o rings making things just that much worse.

[Rahzin]

I'll have to check out your blog. I read a bunch of different posts detailing setting float height, but it's kind of hard to know where to measure to. Most of them say the top of the float, but looking at the carb in the orientation it would be on the bike, the top of the float is up inside the carb, so how could you possibly measure to that? So they must mean the bottom, but then do they mean the bottom seam where it is flat, or the bottom of the bubble shaped area? I saw some diagrams showing both, so not sure.

I can't actually get the idle mixture screws all the way out because I didn't quite drill out the entire plug. Didn't want to damage the surrounding carb housing, although I guess it isn't really a big deal. As it is, I can get a small flathead in there so I left it at that. They don't appear to be leaking, but hard to say. I replaced most o rings when I bought a kit with a new float needle and seat and some o rings in January, and it's been running very consistently since then, so it doesn't seem like there should be corrosion there. No gas sitting for long periods of time. Obviously I didn't replace the mixture s few o rings since I couldn't get to them then. I also installed pilot jets that were one size up from stock. Doesn't seem to have made any difference whatsoever.

I just got back from a ride to fuel up (got ethanol free gas this time so maybe that will change something), and it's basically running the same as before I changed anything yesterday. Which is weird because you would think that with the mixture screws now equal and the throttle plates now equally spaced, it would run differently. Once it was fully warmed up after a bit of riding, I set the idle speed to 1500rpm, so that should be at the right spot. Mixture screws are both at 3 turns out. It just feels exactly the same as before, and still dies when I come to a stop if I don't give it some throttle for a few seconds. It does kind of sound like a more smooth idle, but it doesn't feel or act any different.

So maybe you're right and there is an air leak somewhere. I'm not really sure what else I can do at this point. Aside from take it to a shop and have them deal with it. I kind of don't want to do that because this feels like something I should be able to do myself, but I guess if I'm at a loss, I don't have many other options.

[mr72]

It's the seam on the float.

And you're supposed to drill a tiny hole in the plug and use a screw to pull it out. If you drilled it enough to get a screwdriver in then it may be hard out pull out. Btw if that o ring leaks then it will just be super rich at idle. It would have to leak a whole lot for fuel to make it outside the carb.