I really need help...this bike is killing me.
Ok, I'm currently working on a 2001 VN750. As far as I can tell, everything is stock. Basically, the problem is that the bike is running extremely rich. Here's the rundown:
The bike backfires, though not so much as before I started working on it. I get black smoke from both exhausts when I roll on the throttle, though not ever singe time I rev it up. The smoke is accompanied by a strong gas smell...and once or twice I've witnessed a couple of fireballs out the exhaust. It gets considerably worse when it warms up, meaning its drive-able when I first start it up, but after a few miles I have to kinda stay on the throttle to keep it from choking out at stoplights. I realize that it probably isn't smart to drive it, I've only been driving it down the road and back in attempts to diagnose problems.
The carbs were cleaned by a bike shop in Lexington, KY. He took them apart a couple of times in an attempt to diagnose the problem. I had the carbs off 2 days ago, and took them apart myself to see if I could find anything he missed, but they looked clean and everything seemed in good shape. I did discover that there weren't hoses attached to the float chamber vents. I'm not sure if that's what you call them, but I'm referring to the two hoses that come off of the middle part of the carb assy and run to a T joint, which runs to the right side air filter box (all of which I learned on this site, so thanks!). I bought some 5/16 hose and a T joint and installed those when I put the carbs back on. After the install, I got a new symptom, which was that the bike lost all power under load, cutting out whenever I got it around 4000 rpms. I then tried capping that vent hose...and the bike ran great for the first time since I've had it. That lasted for about 15 miles, then it reverted back to its old state of running extremely rich and choking itself out.
When I put the carbs back on, I cleaned the spark plugs and reinstalled them. I removed them after the ride, and they were pitch black again. Based on the plugs, I'm pretty certain its rich on both cylinders. I've currently got the mixture screws at 2 1/4 turns, though I've had them from 1 1/2 to 3 turns in the last two weeks while trying to figure out whats going on, and I really can't tell much difference in the way the bike runs no matter what they're set at. I checked the numbers on the jets when I had the carbs apart, and they're factory size, unless the previous owner drilled them out or something, and I really don't know how to check that. I only know that the numbers on the jets were 132/38, which is what the repair manual calls for.
I've done tons of reading on this site in the past few months. The bike was purchased in May and was in a shop for 3 months, and all of that time I was reading on here trying to diagnose the problem, while also corresponding with the mechanic. I'm just kinda at wits end here guys, and I'd really appreciate anything anyone can suggest. I've replaced the whole ignition system pretty much, meaning the igniter box, the coils, the plugs, the plug wires and the plug wire connectors. The shop changed the choke plungers, cleaned the carbs, replaced the stator and the voltage regulator, along with a million other things. I don't know what other info to ad, but I'll answer any questions to the best of my abilities, I'll take pics, and I'll try to do whatever anyone can suggest, though at this point I've gotta try to stay cheap because I'm almost out of funds from working on this damn thing and paying the hefty bike shop bill.
I've considered doing an ear shave and rejetting to see if that has any effect, but I honestly don't even know if its fuel or air that's causing my problems. I really thought about ordering new float valves and pins, but it seems unlikely that they would both be bad, since it seems like its equally rich on both cylinders. That implies that the problem isn't just in one of the carbs, right? To give you an idea...I filled the bike up after I finished reinstalling everything, rode a little less than 50 miles, and now I've got a little over 1/4 tank of gas left. It's literally drinking fuel.
Thanks in advance, and I'm sorry this post is so long. I was trying to be as detailed as possible. And sorry again if I left out any necessary info.