'81 cb650c , all four carbs overflow out the throats
Posted: Sat Jan 02, 2010 9:44 pm
I have a 1981 Honda CB650C that I picked up for a song. I have thoroughly cleaned the carburators, and they are extremely clean at this point.
However, since putting them back together, they overflow. Not out of the drain at the bottom of the carbs, out of the intake hole (the throat?).
There is one thing that might be changing things though - the vacuum "tee" hoses that connect carbs 1&2 and carbs 3&4 were excessively rotted, and so I have simply used a small rubber hose to connect the two carbs instead of teeing them to the single line that goes back to the airbox.
Testing I've done: The float valves work. If I take the bowls off, send gasoline to the carburators, and lift the floats by hand, the gas shuts off to the floats I have lifted. If I turn the carbs upside-down, and apply gas (from high above the carbs), no gas flows into where the bowls would be. If I lift the floats slightly, gas starts bubbling into the carburator. It does not appear that the float valve seats are pitted or filled with junk. The float valve dealies look just fine. There is no way to adjust the float height - the floats are 100% plastic, and there's no way to try to adjust the float valve to adjust the float height.
I have first, this question: The diaphragm above the carburators shuts off the flow of gasoline to the carburators unless the engine is turning over. So, do the little vacuum tees somehow limit the flow of gasoline to the carburators when the engine is running? So, if there's a vacuum to the vacuum tube to the gas diaphragm thingy, maybe the vacuum from the airbox to those little tees on that connect to the carbs provides a way for the carbs to additionally shut off, or request less gasoline?
The only bit I'm missing is whether or not those vacuum "tee"s actually help hold back the flow of gas, or something. Unless the floats are sticking once I put the carb bowls on, there's no other reason I can find that would cause all four carbs to overflow out their throats when gas is flowing to the carbs.
My next test, when I can, is to take those joining tubes off of carbs 1 and 2, and see what happens when I let gas into the carbs. SEcond, is to connect one of the carbs with a tube, and apply a gentle vacuum when I deliver gas to the carbs... Unless you guys have a solution for me
However, since putting them back together, they overflow. Not out of the drain at the bottom of the carbs, out of the intake hole (the throat?).
There is one thing that might be changing things though - the vacuum "tee" hoses that connect carbs 1&2 and carbs 3&4 were excessively rotted, and so I have simply used a small rubber hose to connect the two carbs instead of teeing them to the single line that goes back to the airbox.
Testing I've done: The float valves work. If I take the bowls off, send gasoline to the carburators, and lift the floats by hand, the gas shuts off to the floats I have lifted. If I turn the carbs upside-down, and apply gas (from high above the carbs), no gas flows into where the bowls would be. If I lift the floats slightly, gas starts bubbling into the carburator. It does not appear that the float valve seats are pitted or filled with junk. The float valve dealies look just fine. There is no way to adjust the float height - the floats are 100% plastic, and there's no way to try to adjust the float valve to adjust the float height.
I have first, this question: The diaphragm above the carburators shuts off the flow of gasoline to the carburators unless the engine is turning over. So, do the little vacuum tees somehow limit the flow of gasoline to the carburators when the engine is running? So, if there's a vacuum to the vacuum tube to the gas diaphragm thingy, maybe the vacuum from the airbox to those little tees on that connect to the carbs provides a way for the carbs to additionally shut off, or request less gasoline?
The only bit I'm missing is whether or not those vacuum "tee"s actually help hold back the flow of gas, or something. Unless the floats are sticking once I put the carb bowls on, there's no other reason I can find that would cause all four carbs to overflow out their throats when gas is flowing to the carbs.
My next test, when I can, is to take those joining tubes off of carbs 1 and 2, and see what happens when I let gas into the carbs. SEcond, is to connect one of the carbs with a tube, and apply a gentle vacuum when I deliver gas to the carbs... Unless you guys have a solution for me