so, my 73 AT3 had a cheap carb on it that the float kept sticking and was dumping fuel on the ground. I would beat on it with a crescent wrench until it stopped, otherwise it ran fine. then I finally gathered the parts to build an old Mikuni VM24 that I got off ebay, I meticulously cleaned and assembled the Mikuni, put it on the bike, and it instantly dumped so much fuel that it came out of the exhaust at the cylinder head port. I had to remove the exhaust and pour about a cup out. I must have had the carb off 4 times after that and can't figure out why it's doing this. Maybe the float is wrong or bent somehow causing it to hang up and never close the float valve? the float assembly floats out of the carb, and theres no liquid inside of it. I tried just blowing into it right side up and upside down, and it closes then and stops the flow of air. any ideas? My other thought is the oring in the bowl...maybe it's not sealing?

There's approximately 285,672 variations of the "VM24"...  did you get the original Yamaha version for your year/model?  What are the numbers stamped on the flange?

Pictures would be helpful.

Float level?

I will get some pics next time I get back to the bike and working on it. It came from an AT3 the guy was parting out. There are no numbers stamped on the flange (bowl flange)
I never looked at the two bolt flange that bolts to the reed valve housing

float arm is level (level-ish) with gasket surface. but it was in pretty rough shape

It has a 200 main jet which is correct for the AT3, I think

I'm ordering a new float, If I can't make this one work, then I will just think about getting a new "better" Chinese one. I really just want stock everything though. I know I can buy a brand new Mikuni, but it's round on both sides and the inlet side won't let me use the airbox and air boot

 

Yes, numbers are normally stamped on top edge of mounting flange. I might have one or two of those carbs or for sure some parts.

If you want to ship the carb to me I can see if I can figure out the problem with the flooding.

I will take you up on that offer Mark, I’ll get that new float and send it along with the carb. I’ll PM you when I get it all together to send. Happy New Year!

update:
I got the new float and absolutely nothing changed. when I first got it in, everything seemed ok, but as soon as I started kicking the bike fuel poured out both the exhaust and carb throat. I took it back off and used water and my best guess is that the hole in the bottom of the bowl is eroded to the point where fuel just siphons straight through, bypassing the jet and going straight up the passage into the throat of the carb. There's only 2 ways fuel can get up to the slide needle and venturi, right? either through the hole leading to the jet, or through the oring joint on the pipe that leads up to the venturi and needle-or am I wrong?
The float picture is the old one that came with the carb. looks like it was ok
numbers on carb flange Mark

It might be just an aberration in the photo, but it sure looks like the overflow tube in the bowl is split. This would let incoming fuel run right out the overflow hose.
alnarv

I'm pretty sure the tube is not split, but even if it was, the bowl would never fill, and the fuel wouldn't pump out of the bowl/main jet circuit straight into the carb, would it?

I understand concerns about o-ring seal in bottom of bowl...  a bad one or eroded surface can definitely make bike run rich as it bypasses main jet.

The thing is, you could remove all the jets from the carb...  slide needle, everything...  and while it wouldn't run, it would not pour fuel into the engine or have fuel pouring out the carb throat.

Something in the float system is allowing the fuel level to get too high.  Obviously this could be float level setting, a bad float, or a bad float needle and seat. 

Less common but I've seen it is the float needle seat is leaking around the threads/gasket but that usually results in "slow flooding"...  more of a "drip" overflow.  I've only seen this once.

More common thing I've seen that fits your description and float parts all good is a hole corroded in carb body so that the fuel bypasses the float valve completely and just dumps into the bowl.  Do you have a picture of the bottom of the carb with the float and float bowl removed?

I still don't mind looking at it for you or I can look for a 316 carb...  I'm pretty sure I have a couple of them in my old carb box. 

I don't have a picture, but I will get one next time I have it off. I will just clean it up and get it ready to send to you then. I have worked on more than a few carbs, but never seen any dump this amount of fuel. when it's doing the dumping, I can watch the fuel coming straight up through the orifice that the needle goes up and down in. I guess a breach of some sort in the carb body that allowed fuel to enter that circuit could do that