Topic: carbs on a '75 CB750

[nunnik6]

Hello all!!! I just joined today and thought I would pick a few brains....

Ive got a '75 CB750 K5 that I am rebuilding and Ive got a question about the carbs. I am looking for a diagram or an explanation as to how the gas actually shuts off with the floats and the float valve. The gasoline does not come from the float valve, but through a hole in the top of the bowl section. The float valve leads out to air. My question is is when the float valve closes, does that restrict the air which takes away suction/pressure so the gasoline does not enter or what??? Ive got the problem that the carbs are letting in so much gas that it is emptying into the airbox, onto the ground, and over the bowls and onto the motorcycle.

Thanks for your help!!!

[Sam Green Racing]

Welcome to the forum Nunnik6,

You may have a worn or sticky valve.

When it starts to flood, somtimes a tap on the carb that is leaking with the handle of a screwdriver or likes will stop it.

If it is worn and continues to flood, you need replacement valves.

Plenty guys on here with loads more experience will help, the advice I have given is for most carbs in general.

Good luck.

Sam.

[bryanj]

If, as you say, the float valve leads to air then something is put together way wrong as gas should come through the float valve so it can be stopped when the float lifts and closes the valve.

[nunnik6]

When I put on a gas line and blow into it, the air does not come out of the float valve like I thought. It comes out a tiny hole in the top part of the bowl section.

[cd811]

hondachoppers.com has some good diagrams. you should be able to pull the pin that holds float in place. then pull valve out. the valve seat screw out. clean all of this, then reassemble. float must be set at proper height. if after this it still leaks, the valve and/or seat needs to be replaced.

[scondon]

Sounds like you've hooked the gas line to one of the "vent" nipples.

[nunnik6]

thats what I thought too, about the exhaust nipples. All four carbs sit on the plate and there are supposed to be t-connectors(which I dont have and would like to know where to get them) that attach to the intake nipples and split gasoline from one line. The intake nipples are only about an inch from each other and facing each other when the carbs are all on the plate.

I went out last night and blew air into the intake nipples and the air only comes out the hole at the top of the bowl section/bottom of the carb mechanism and not the float valve. The first two pictures will hopefully explain... on picture 12, the right pinhole leads to the intake nipple, the left pinhole leads to the exhaust nipple, and the float valve hole leads to a hole on the side of the carburetor, as seen on picture 13.

[scondon]

The large holes by the air intake are where the gas lines/pipes go. They are short sections of pipe and the one between carbs 1 &2 will have a nipple to attach the gas line from tank. The small nipples towards the middle of the carbs are for the air vent vent lines.

   If your missing these connector lines it might be a good idea to just get another set of used carbs and keep your current ones for spares. I'm sure it would be cheaper and give you more time to devote to the rest of the project.