Fuel coming out of intake boot

[Handyman1018]

1983 CB650SC, 23K miles

When I shut the bike off I get some fuel leaking out of the intake boot (at the clamped joint between airbox and carb).   Searching the forum this appears to be a case of the float hanging up causing fuel to get past the float needle.  So I pulled the boot back to look into the carb and sure enough there is fuel rising up from the carb, and flowing back into the boot.   This is happening only on the left most carb (#1) which makes getting at it a little easier.   I should mention that I rebuilt the carbs last year and have had no problems with them until now. 

So I dropped the #1 bowl which allowed me to pull the float pin, remove the float and float needle.  Everything was spotless.  I squirted a little carb cleaner up the main jet air passage just in case something might have gotten stuck up there.  Put everything back together and unfortunately the problem remains.

Before I pull the bank of carbs off to go thru #1 carb again are there any suggestions on things I might want to try with the carbs on the bike.   

Appreciate your comments. 

[coffee_brake]

The float needle--the thing the float pushes up and down that seals the valve--if you can see AT ALL where it has touched the carb, it's bad. Usually it is the #1 carb that goes bad first. Even if it looks perfectly clean, any wear whatsoever on that grey (or red, or black) pointy part will let fuel come through, just like you are experiencing.

If you get a new one, then you can also polish the seat. The brass thing that the float needle goes in can be smoothed out by putting aluminum or brass polish on a Q-tip, and then spinning the q-tip on the seat where the needle sits. It will make the seat smoother for your new needle.

[Handyman1018]

Hey thanks for the tip.  Ordered new float needle (actually had to order 6 of them).

Cleaned the seat with a Q-tip and some metal polish (it was dull, now shiny) which was a nice trick.  

Installed the new float needle.  

Took bike for a ride, initially all was well.  Parked bike for 1/2 hour and came back only to find gas on the ground... carb #1 still leaking.  Went for another ride and bike had no power.

The leak is now occurring while the bike is running.  It is a slow but constant drip of fuel between the carb and the intake boot.  I pulled the plug on the airbox vent line and sure enough it was full of fuel.  Likely fuel in the oil as well but will get to that in time. 

A friend said it is likely a check valve in the carb... anyone familiar with this?

Appreciate your suggestions. 

[coffee_brake]

Did you order float needles specifically from Honda, or did you buy the K and L brand of float needles (usually blue packaging)?

K and L sometimes is not a straight fit and then the floats have to be adjusted.
If you got Honda needles they should fit right the first time.

Two things must be wrong for the carb to be leaking fuel when the bike is not running, and the bike has a vacuum petcock.
First, the petcock is not working right, it is letting fuel out of the tank even when the vacuum system is not operating. Some petcocks are easily rebuilt, sometimes you might have to source a different part for it.

Second, the float needle is not seating and the fuel is flowing into the carb even though the bowl is already full of fuel. This can be caused by the wrong type of needle, a bad float, or a float out of adjustment. I think more experienced folks will speak up and add to this.

I don't know of a check valve on this kind of system. The checks are the vacuum system on the petcock and the float needle, which is supposed to close when the carb has enough fuel in it.

I already learned this summer about the K and L float needles being different from some stockers. Doesn't mean they won't work, but it means you gotta adjust the floats, if possible.

[Munkey]

The carb floats are meant to meter the fuel into the carb bowls on a running engine. They are not designed as a fuel shutoff, that's what the petcock is for.

If you have a lot of fuel leaking when the bike sits, then you need to look at the petcock.

[coffee_brake]

But if the float needle is not seating correctly, due either to a bad needle or mis-adjusted float, AND if the petcock is faulty as well, this fuel flooding will occur, right?

[Laminar]

But if the float needle is not seating correctly, due either to a bad needle or mis-adjusted float, AND if the petcock is faulty as well, this fuel flooding will occur, right?

Yes. I can leave the petcock open on a non-vacuum actuated petcock and the float valves will shut off fuel from flowing into the carbs.

[Munkey]

But if the float needle is not seating correctly, due either to a bad needle or mis-adjusted float, AND if the petcock is faulty as well, this fuel flooding will occur, right?

Yes. I can leave the petcock open on a non-vacuum actuated petcock and the float valves will shut off fuel from flowing into the carbs.

But my point was, that even if the float does not shutoff the fuel, it does not mean they are faulty. That's not what they are designed to do. The problem may be just with the petcock.

[coffee_brake]

Right, of course. 

The petcock should be put to rights before doing anything else.

But the fact that fuel is coming out of #1 cylinder means two things: the petcock is faulty, and also the #1 float valve is not closing effectively.

Right?

[Laminar]

Yes.

[Handyman1018]

Thanks for the advice. 

Petcock is fine i.e. without vacuum there is no fuel flowing from it to the carbs.   I tested this by pulling the fuel line entering the carbs (no fuel flowing).  Then I pulled a vacuum with a small hand pump that I use for bleeding brakes and fuel flowed like mad. 

OK so I polished the needle seat as a member suggested... made things nice and shiny but leak did not go away.  I pulled the top off the carb and carefully took the slide and needle out.  Then with the same hand pump I pulled vacuum again at the petcock.  Now with a clear view of the main jet opening I could see fuel flowing into the carb.  Conclusion, float needle is not seating as it should.  Yes the needles are K&L and it seemed to me that the diameter of the rubber tip was IMO just a little smaller then it should have been. 

So the interesting thing about this story is I have had the bike up for sale for a few weeks.  A guy showed up this AM and bought it, carb leak and all.   Bittersweet to see it go.  I will not get to finish the story but I suspect you are right... the needle needs to be addressed.

Thanks again for all your help with this.  The 650 is gone and I am on the hunt for a 700S!

[Moedad]

This was a great little thread. Short and to the point, with good info.