Motorcycle Repair: 1981,750,honda,c, honda cb750k, 750 honda

Question
Dear bill,please try to help.Our bike will not start. It will run on starter fluid. We paid a guy to redo the carbs,i put them on and they leaked. At the vac. Regulater. I bypass it to put gas directly to the carbs. In the fill pipe on the left side. I took out the float bowl drains,and the carbs were dry. All 4 of them! I also have the airbox and filter on. I crank it over fast too. Fires on either.put gas in 2@4 an it fires too. No gas! This is from a homemade clear plastic bottle gas tank and clear hose.l hang it from the handlebars,plenty of fall. Thanks John

Answer
John, if the fuel shut-off has a bad diaphragm, it may be the same size as those of the air cut valves or other small diaphragms. If you can't find a suitable substitute, then you will have to recreate the pre-81 fuel hose circuits for that model.

Note that if the auto shut off valve diaphragm is okay, you need to apply vacuum to the carb fitting line temporarily until it fills the carburetors. You can't get sufficient vacuum signals while cranking with starter motor long enough to fill all four carbs before the battery dies.

http://www.cmsnl.com/honda-cb750k-750-four-k-1980-usa_model7245/partslist/F++13.

vs.

http://www.cmsnl.com/honda-cb750k-750-four-k-1981-usa_model7246/partslist/E++19.

Remove all the auto shut-off plumbing, cap off the vacuum line fitting at the #2 carb and run fuel directly from petcock to the fuel inlet fitting at the carburetors. If there are two fuel fittings on the carb rack, then you will have to use a T or Y fitting to feed both from the single petcock line.

Bill Silver