Pulling WAY too much fuel under load (upon take-off)


CB750 New member
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Battle Creek, MI
I helped my son pick up an 83 CB750 Nighthawk last year, supposedly with 4,200 miles on it. It had been sitting awhile, so naturally the carbs were left with crap-gas in them and were in rough shape. It actually ran and went down the road, but low-end was pathetic and it kept wanting to high idle once it warmed up. After my son had already been riding it for half of the summer, I talked him into letting me have it so we can get it running properly (and safely).

I ended up getting new intake boots, as the originals were hard as a rock. Then I tore the carburetors down and soaked them each in a gallon of carburetor cleaner for two days. The rebuild kits were Chinese (off of Ebay) and after using fine cleaning rods to insure all ports were open in the carbs, I blew them out/off with compressed air and reassembled them. One of the things I noticed was that the all-plastic floats had zero adjustment ability to set the float height. I took a chance and used them anyway and at first the bike started up immediately and had excellent throttle response (which it didn't before). I ran the idle screws out to 3/4 turn, and it seemed to idle low and smoothly. BUT.......when I went to take it for a test spin, it immediately bogged hard when I attempted to take off. As I rev'd it to around 2,500-3000 to take off, as soon as I started letting out the clutch and put it under load, it immediately bogged and loaded up with fuel. I had to sit there and keep the throttle a good portion open until the black smoke cleared out and it slowly started to idle once more. This scenario would last for about 20-30 seconds until it could burn through the amount of fuel it was chocking on and start idling properly again. I played with it a little more and found that if I turned off the fuel completely (and gave it a few seconds) that It would take off from a dead stop nice and smooth, but would quickly run out of fuel and start running lean. As soon as I turned the fuel back on and tried to accelerate it would bog and run uber-rich once more.

SO......I just finished replacing the all-plastic floats with Honda GL1100 plastic/metal floats so that I can actually adjust them to the specified 15mm starting height that was recommended online. After putting the carbs back together I fired it up and it ran nicely like it did before. But......as soon as I attempt to take off it loads up with fuel just like before. I feel that there is something simple and obvious that I am missing. I can't seem to find this particular problem in the forums, so If it already exists, please feel free to point me in the correct direction. Otherwise any advice would be extremely appreciated.