I bought a low hour YZ426 from a friend, the bike has been sitting for 1-2 years. My friend was going to get the bike running before I bought it and he split the carb in half, like the way you're not supposed to. Since Yamaha doesn't make a gasket for that seal, I figured I'd try some sealant. Well, it started and ran, but wasn't quite right. Rather than chase my tail, I figured i pick up a used carb and save myself the hassle. I found a good price on a clean '04 450 card and read this thread: http://www.thumpertalk.com/topic/802827-carburetor-question-on-my-yz426/ - so I figured I was good to go. The carb shows up and I should have cleaned it, but I slapped it on and the bike wouldn't start. I figured the pilot was gummed, so I cleaned the pilot and she fired up. At this point, I had the '01 plunger screwed into the top of the carb, instead of the '04 plunger cable. The bike ran okay, not quite like it should, plus it had a little bit of a hanging idle. It was also popping on decel, but the bike sounds like there is no packing left. So, I figured I'd take it all apart and clean it thoroughly, plus install the proper plunger cable even though the clutch perch+hot start lever has not shown up yet. Then the thing won't start at all and fuel was dumping out of the bowl. I figured the float was stuck so I pulled the drain plug and jiggled the float with a tie-wrap, no more leaky. Still won't start, but no more fuel dumping out the carb. The bike also has a weird issue after I tried to bump start it. I pushed it for a few seconds with the decompression lever pulled into try and clear it out in case it were flooded. I figured it wasn't a big deal since the manual states you can kick it with the lever in to clear a flooded motor. It never fired or ran with the decomp lever pulled in. Once I was thoroughly exhausted after pushing that bish up and down the street, I went back to kicking on the stand. Well, you could kick and kick and it would never hit that hard compression stroke. I figured I must have wrecked the exhaust valve by pushing it with the decomp lever in, but after kicking it ten time, it's now kicking as normal, rock solid on the compression stroke. So, maybe the cable was just sticky..?? Also note that I have never touched the TPS on either carb. Unplugging the sensor doesn't seem to have an affect on starting. Sooooo, I just went back and pulled the bowl thinking maybe a piece of debris is in the pilot again, but nope, all jets clear. Plus, I put the old '01 plunger back in because I felt like I was having better luck as in the beginning on the second paragraph above. I can get the bike pop and sometimes run for a few seconds, but it dies on its own, or it dies the moment I touch the throttle. Here's the strange part, this is very repeatable - if I pull the choke and make it pop, I can then get it to run a few second with the hot start in. If it won't pop or fire with the hot start on, I just pull the choke until it pops, then go back to the hot start to make it run a few seconds. The fact that the hot start needs to be on would make you think it's super rich, but why does it want the chock on briefly? I was thinking that maybe there was some weird vacuum thing going on, the gas cap valve is working correctly. There seems to be good flow from the fuel line, so I don't think the filter in the tank is plugged. I adjusted the fuel screw a bit, it won't do anything with it all the way in. The above is with it at 1.5 out, I haven't tried backing it out more than that yet. The pilot on both carbs is a 42, not sure of the needle position, I'll check that tomorrow morning. The bike has spark and good compression, again it's a really low hour machine, I'd guess less than 50hrs. I haven't checked the valve clearance, but given the fact that the bike was running pretty decent (ripping wheelies through the neighborhood like a 16yo from Baltimore) and considering all the carb oddities, I really feel it's carb related. I'm spent for today, any tips for tomorrow would be much appreciated!