1980 Honda CB750C leaking fuel from carbs

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fourmj

New Member
Hey guys, I just finished wiring my 1980 Honda CB750C and I tried to run it. The electronics work fine, but there's a lot of fuel leaking from the carbs and I'm not sure why. These carbs haven't been altered in any way since they were taken off the bike 4 years ago. They've been wrapped in bubble tape and stored in my basement since then. I also put on a new air filter (this one: https://cognitomoto.com/products/cb750-air-intake-box-sohc-and-dohc).

Here's a video of the fuel leaking from the carbs (this is also running without the exhaust pipes on, but I don't think that should matter): https://goo.gl/photos/A89gGsYWiSm1r2vk6

Any help on this would be appreciated!
 
Does it stop leaking when it's not running? Maybe that air box is too restrictive causing a vacuum and pulling fuel up.


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Tune-A-Fish© said:
Does it stop leaking when it's not running? Maybe that air box is too restrictive causing a vacuum and pulling fuel up.


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Click to expand...

It still leaks even when running.
 
So to answer my question... it leaks just sitting with the petcock open? If that's the case your float valves are not seating allowing fuel to flow through.

Pull em off and check float heigh and buoyancy. If you have rubber float needles they could be fubared or dirt is lodged in them from a dirty tank.


Sent from my iPhone using DO THE TON
 
Tune-A-Fish© said:
So to answer my question... it leaks just sitting with the petcock open? If that's the case your float valves are not seating allowing fuel to flow through.

Pull em off and check float heigh and buoyancy. If you have rubber float needles they could be fubared or dirt is lodged in them from a dirty tank.


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Click to expand...

Yea, it leaks even when the fuel switch is on off (this is after running though). I think you're right about the floats though, I'm pretty sure that's what the problem is. There was a lot of dirt in the tank and I don't think I got all of it out before running the bike. Thanks for the help!
 
Sure! No matter how clean you get the tank run an inline filter to catch the micro particles and save yourself the grief.


Sent from my iPhone using DO THE TON
 
fourmj said:
Hey guys, I just finished wiring my 1980 Honda CB750C and I tried to run it. The electronics work fine, but there's a lot of fuel leaking from the carbs and I'm not sure why. These carbs haven't been altered in any way since they were taken off the bike 4 years ago. They've been wrapped in bubble tape and stored in my basement since then. I also put on a new air filter (this one: https://cognitomoto.com/products/cb750-air-intake-box-sohc-and-dohc).

Here's a video of the fuel leaking from the carbs (this is also running without the exhaust pipes on, but I don't think that should matter): https://goo.gl/photos/A89gGsYWiSm1r2vk6

Any help on this would be appreciated!
Click to expand...

I had the same problem after I started the bike from coming back from a month of working. It stopped after the bike warmed up. I could only assume it was time to replace all the rubber bits in the carbs. I ordered a rebuild kit. Havent put it in though. If your floats were flooding, it would bleed from the overflow port at the bottom of the bowl, not around the seam where the bowl meets the carb body, or from the fuel rail.
 
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