750 Carbs (Again)

Posted by RCOBill on Mar 29, 2013; 6:52pm
URL: http://vintage-and-classic-hondas.81.s1.nabble.com/750-Carbs-Again-tp4038640.html

Hello all, new to the site and first post..  (1981-82 CB 750 all stock)
Another VB42A carb problem (I Think) to resolve. I can turn a wrench and have rebuilt a few carbs in the past but the VB's are a challenge for sure. Buddy's bike and this started as a favor to rebuilt carbs that is now on its 4th month and still on SQ#1.  Bike sat for a year with fuel in the tank and the fuel valve open, the result was green junk and a mess. Went through the rebuild process three times, new O-rings, new jets, maim and idle, new diagrams and gaskets. Checked the rubber boots between block and carbs, returned the setting back to where they were before stating, used fresh fuel and still will not run at idle, mid-range or high RPM. Starts on full choke and dies, pump the throttle, revs and dies. It will keep running with short sprays of starting spray. Running 150 to 152 psi on each cly. and good suction if you crank it and cover the intake on each carb with your hand. The spark is just a little weak in that it’s not that bright blue flash you like but it does start and run, so it is there. Same feeling with the timing, it can’t be that far off that it will not run, I’ll set that with a light once this problem is resolved and it will idle. I have the carb section of the manual and did checks the bench adjustments as directed. I even used a shop vac and tested the carbs on the bench, full choke plenty of gas, no choke and the pistons pull up to open the mains, plenty of gas. Not a real safety minded check but it worked.  So, with all that said, what is common to all four carbs that I have missed. Additional questions, are the overflow tubes in each bowel also the vents to allow air in as fuel is sucked out? This has the plastic floats, how are they adjust, I don’t see a way to bend anything to change the setting. Last, checked to see what the points looked like, left side eng. small cover removed, found the spark advance in there, no points, I also found oil, not much, but I don’t think there should be any, is that correct and is the electronic ignition?  Also, the throttle pump balls on #2 carb, are working as it pumps fine, visible in the all four carbs and when pumped it revs. I’m lost as this point so please help.. Thanks