• Enter the March CB750 Supply gift certificate giveaway! It's easy... Click here, post something, and you're entered into the drawing!

everything was fine, until i smelled fuel

lkstk

CB750 Enthusiast
Messages
30
Reaction score
0
Points
6
Location
United States
let me start by stating that i am a novice at motorcycle maintenance, and i am trying to learn more as i do it all. i removed the carbs on my 76 Cb750F super sport to clean them and install new jets and gasket. after installing the finished product, i opened the fuel valve and fuel started leaking out. i found the source at carb #2 coming from a brass fitting identified by the red arrow in the picture below. it sounds an awful lot like the carbs are coming back off, but can anyone tell me what this is, and what i may have done wrong? it is only leaking from the one carb, so hopefully it will be an easy fix. or an excuse to buy a set of CR29's! any help would be greatly appreciated.

photo.jpg
 
let me start by stating that i am a novice at motorcycle maintenance, and i am trying to learn more as i do it all. i removed the carbs on my 76 Cb750F super sport to clean them and install new jets and gasket. after installing the finished product, i opened the fuel valve and fuel started leaking out. i found the source at carb #2 coming from a brass fitting identified by the red arrow in the picture below. it sounds an awful lot like the carbs are coming back off, but can anyone tell me what this is, and what i may have done wrong? it is only leaking from the one carb, so hopefully it will be an easy fix. or an excuse to buy a set of CR29's! any help would be greatly appreciated.

View attachment 2623

That is an air vent for the needle jet emulsion tube. (The other one is for the mix screw/slow jet circuit.)

If fuel is coming out of it you have at the very least a malfunctioning float valve AND a clogged overflow.

Just because it's an easy fix is no reason to pass on the CR29's. LOL.
 
That is an air vent for the needle jet emulsion tube. (The other one is for the mix screw/slow jet circuit.)

If fuel is coming out of it you have at the very least a malfunctioning float valve AND a clogged overflow.

Just because it's an easy fix is no reason to pass on the CR29's. LOL.

no, the struggle with the CR29's is the money! but thanks for your help. i wonder if i put the float valve in upside down. or maybe i loosened up some junk while cleaning it?
 
Your float seats are without individual filters so if a teensy bit of crud comes loose it'll hang up at the sealing surface and hold the valve open. Remove the needles and flush filtered gas through. If this doesn't fix it you'll need to replace the needles and/or seats. Use high-quality (ie Keyster) rubber tipped needles. Never put unfiltered gas through them, and use new fuel line. Once they're tight they'll stay that way for years to come.

(Admin: remove this line if it's verboten to hawk wares but I've got orings, float parts, etc.)

Let's also ensure that the float heights are correct.

Not knowing to what extent you tore them down, it's never a bad idea to make sure that the jetting and needle clip positions are correct for what you're doing, and that the small passages are clear.

And of course the one thing I preach to everyone is to have a look at your compression. (And valves, and timing...)

I know we're getting far afield of carbs, but around here we're focused on the long haul.

For example, a guy can install pods or drag pipes without sufficiently richening the carbs. He may THINK that he's running just fine in a lean condition but a year later he burns a valve.

Down low we can be a tad lean for easier starts and take-off response but up high we want to be rich just this side of losing power. It's a balancing act of sorts but it'll keep you going longer.

OSC
www.oldschoolcarbs.com
There are 10 kinds of people in the world---those who understand binary and those who don't.
 
thank you both for your help. i took it apart tonight and found that not only was the float valve needle MISSING! but it wasn't anywhere in the shop. so i must have accidentally thrown it out with the old parts. it must have happened when i took them back apart (after adjusting the float levels). oh well, more lessons to learn after this one i'm sure.

btw- old school guy, those are some really sharp looking rebuilds on your site! maybe in the future i will use your services.
 
Back
Top