Topic: Newbie Carb Question

[Mike.n.Ike]

Hello
I just recently joined this website but I am most certainly not new to it. I have been referring to the knowledge in these forums that has aided me in completion of a top end overhaul of my 1972 CB750. I first want to thank all of you for organization and such great posts the members of this site have offered.
I know this is not an introduction forum but I am pre med major going into my senor year and have always been mechanically inclined just because I'm curious of how every thing works. My father and I have spent the past few years to complete restoration of a '67 chevelle ss for my younger brother.  Wanting to try my own personal project, after many months of research I chose to  purchase my CB750 mainly due to the simplicity and vintage appeal. After riding the bike for the first time I immediately fell in love with it.
When I purchased the bike it ran but was a little on the rough side. The PO had recently rebuilt the bottom of the engine including the transmission. So upon restoration I chose to rebuild the top end. Compression, seals, valves, etc were all done to the chlymer manual and shop manuals. Just to make sure I brought the bike to a 40+ year Honda mechanic and every thing checked out to be in tip top shape.
Sorry here comes my question finally! Until recently the bike ran phenomenally until I noticed that carb 1 was leaking some gas into the air box and a little out of the excess hose. I figured this to be the floats since to my knowledge they were the original 50 year old ones. I purchased all 4 replacement floats for good measure. When I actually removed the float bowl of carb 1, I realized I put the float upside down (duh moment).  At this point the floats have not arrived in the mail so I decided to tinker with the carb a bit and see if my assumption of a faulty float was indeed the problem. Well messing around with the float needle I'm beginning to think that I may have a bigger overall problem of a carb just coming to the end of its life and failing because the float bowl will not fill up with the needle all the way down and the engine running. So my question is, am I not seeing some thing else that could be producing this problem? I cleaned but didn't replace any carb components when I went through the bike. I'm currently back at school in Arkansas (the bike is in Texas) so I'm not exactly in a position to work or even examine the bike. I just made sure I got a good look of every thing before I left.
Any questions or comments back would be greatly appreciated!!
Thanks a lot.

[MiGhost]

I'm not sure if the early 750 carbs have the small beenie screen filter on the top of the float seat, or not. The seats are removeable on the early carbs. Check to make sure they are not plugged on the top.

[dgedinyte]

If I'm reading your description right, your saying that with the floats at the bottom of their travel and the float needle all the way out, your getting no gas to that carb. If that is correct then you should check the passage from the petcock to the carb for blockages, as well as(and more likely your culprit) the intake hole in the carb where the gas goes in. You should be able to spay carb cleaner in there with a straw, and see it come out the bottom. Lastly and least likely your needle needs replaced. In my experience, a bad needle would not stop the flow when depressed and the bowls overflow. But I suppose maybe it could fail in reverse.

[Mike.n.Ike]

Awesome thanks for the quick replies. I'll post again when I'm able to find time to tinker with it. I appreciate it

[ekpent]

Lot of writing there  So is the problem that no matter what you do the bowl is not getting gas in only one carb ? If so then look for a clog behind the seat where the float needle rests, a fuel supply rail and/or make sure the vent tube is clear.  Also the earlier carbs do not have the little filter attached to the needle float seat.

[harisuluv]

What you are describing sounds like floats upside down.  However, you're saying that floats upside down is right side up.  All you changed was the float to the "right" position and now it doesn't get gas.  That's exactly what happens when it's upside down.

Having the engine running pretty much has nothing to do with the gravity feed of gas to the carbs. 

One of two pictures would be enough to eliminate the majority if your problems visually.

Did you measure the float height?