QuestionI just purchased a 1974 Honda CB750 what I have Noticed I have one carb that leaks from the bowl,is the best I can tell. I noticed it sitting I don"t know about riding. Is there a seal or o-ring bad? And how hard of a job is it?
AnswerCarbs leak due to worn/dirty float valves, incorrect float levels or sinking floats (pinholes in the brass float).
You can shut off the fuel, disconnect the drain hose at the bottom of the bowl and drain the float bowl via the bottom drain screw OR just unsnap the bowl clip and carefully remove the bowl to a container to dump the fuel into. Easier on the outside bowls than inside ones, obviously.
Look carefully at the bottom of the bowl to see if there is a sign of water, dirt or other debris that has come down the fuel line system from the tank and petcock. I would check the petcock bowl and screen upstream for signs of the same.
If you have nimble fingers, you can slide out the float pivot pin and remove the float and the float valve needle, with the carbs in place. The float valve seat screws into the body and can be removed with a 10mm socket, as I recall.
Inspect the seat for wear or dirt/debris that often gets trapped behind it, as well as a close look at the needle for signs of wear or damage. Shake the float and listen for the sounds of fluid inside. If so, then you have to replace the float or find someone who is skilled at soldering the hole up.
Correct float level setting is 26mm, measured at the far edge of the float, as the small tang is just resting on the end of the float needle, but not compressing the spring loaded tip.
Sometimes, it is just a matter of cleaning out some dirt and sometimes, if the bike has been sitting or has high miles, the valve assy should be replaced.
More help on early 750s is at www.sohc4.net
Shop manuals can be found on Ebay auctions, www.motorcyclememories.com or www.helminc.com
Bill Silver
