Just because you've gone through the carbs a dozen times over the course of months or years, checked everything MANY times, and synched them suckers more than you thought would ever be necessary doesn't mean you're done. I've read something about this on here a few years ago and had completely forgotten about it until last night as I was trying to fall asleep.
Ready...
Your 30-some year old carb floats ARE NOT GUARANTEED TO FLOAT THE SAME!
I've had 1 cylinder that never quite seemed right. She started slow but it would always get a little better when she got warmed up, just never exactly right. Yesterday I switched out some D8EAs I had run for only about 50 miles just to make sure I didn't lean her out too much with Hondaman's ignition advance tweak and #3 was very clean while all the other plugs were sooty enough for me to know I needed to go back to D7EAs. Why in hell would just the one cylinder be lean. They all have the same jets and I KNOW there is no blockage.
This evening after work I dropped the bowl and adjusted the float slightly. She fired right up and ran MUCH better. I still need to synch them again and am going to borrow a carbtune to do it just to try something different. My old mercury unit is a bit beat.
Here's to checking the flotation of each float before you assemble the carbs to make sure they float at the same level. Better yet, build one of those nifty set-ups I've seen a few members build that have a clear tube on the outside of the bowl so you can actually see the level. I'm going to be working on making that before long and get these floats exactly the same. Screw the measurements when dry!
C'ville
