Topic: Caburetor Overflow 1975 CB550

[quidger]

What are reasons that one of the four carburetors keeps overflowing out of the overflow line.

These are the three things that I am aware of that might cause it. What am I missing?
 
(1) the float height adjustment being wrong,
(2) float needle valve being stuck or plugged up,
(3) floats have holes and are sinking

Floats are set at exactly 22mm.

Thanks for any suggestions.

[lucky]

What are reasons that one of the four carburetors keeps overflowing out of the overflow line.

These are the three things that I am aware of that might cause it. What am I missing?
 
(1) the float height adjustment being wrong,
(2) float needle valve being stuck or plugged up,
(3) floats have holes and are sinking

Floats are set at exactly 22mm.

Thanks for any suggestions.

Buy 4 new float valves brand new and install them and make sure the floats are set by the book.

The float valve is one of the mist important and critical parts of the carb.

It does not help to adjust the floats if the float needle is old and worn .

IF it is a metal needle then you have to replace the seat AND the needle.
IF it is a rubber tipped needle you only need to replace the float needle but not the seat.

[quidger]

What are reasons that one of the four carburetors keeps overflowing out of the overflow line.

These are the three things that I am aware of that might cause it. What am I missing?
 
(1) the float height adjustment being wrong,
(2) float needle valve being stuck or plugged up,
(3) floats have holes and are sinking

Floats are set at exactly 22mm.

Thanks for any suggestions.

Buy 4 new float valves brand new and install them and make sure the floats are set by the book.

The float valve is one of the mist important and critical parts of the carb.

It does not help to adjust the floats if the float needle is old and worn .

IF it is a metal needle then you have to replace the seat AND the needle.
IF it is a rubber tipped needle you only need to replace the float needle but not the seat.

10-4. I'll give it a try.

Thanks.

[Stev-o]

4.  Float bowl has a small crack. This happened on one of my 750's. 

Sometimes a light tap on the float bowl with the handle end of a screwdriver will unstick the needle valve.

[TwoTired]

Look at the float needle tips. If steel, they should be nice and conical with no steps.

They "marry" to their respective seat, and don't like swapping about among other seats.

Make sure your fuel supply is clean and have no particles to get between needle and seat.

Check to see if the leak occurs when parked on the center stand.
Make certain there is no swing resistance when the floats are moved to either sideways position, and slide easily against the pin posts.

If the float pin conical tip look okay.  You can "lap" the pins to their respective seats with a little lapping compound.

Always turn off the fuel tap when parked, anyway.  Crud happens.

For the carbs found on the 75 CB550, the seat has an o ring to seal it to the carb body.  If it loses seal, the carb will overflow, even if the float valve needle and seat are perfect.

Check the carb bowl stand pipe for cracks.

Cheers,

[bollingball]

Take a close look at the hinge look for burrs at the post area both sides. I know just where to shut the fuel off so I run out of gas as I coast into the shop

Ken

[quidger]

Look at the float needle tips. If steel, they should be nice and conical with no steps.

They "marry" to their respective seat, and don't like swapping about among other seats.

Make sure your fuel supply is clean and have no particles to get between needle and seat.

Check to see if the leak occurs when parked on the center stand.
Make certain there is no swing resistance when the floats are moved to either sideways position, and slide easily against the pin posts.

If the float pin conical tip look okay.  You can "lap" the pins to their respective seats with a little lapping compound.

Always turn off the fuel tap when parked, anyway.  Crud happens.

For the carbs found on the 75 CB550, the seat has an o ring to seal it to the carb body.  If it loses seal, the carb will overflow, even if the float valve needle and seat are perfect.

Check the carb bowl stand pipe for cracks.

Cheers,

Two Tired:

Not quite sure that I understand the "seat has an O ring to seal it to the carb body" reference.

Are you talking about the float bowl gasket. Sorry to be so dense but I want to be able to understand your point.

Could you please elaborate.

Thanks.

[harisuluv]

The needle valve does not screw in.  It has an o-ring on it and then it presses in.  On top of that is a little retainer clip with a screw.  Without the o-ring gas would leak out the sides.  It isn't precision pressed in or anything.

I actually posted a response to this before but for some reason it didn't post. 

I had a customer who this same problem despite everything appearing to be correct.

First we thought the valve was faulty and it was leaking.  We took the float bowl off and turned the gas on--when the float was raised the valve closed properly and stopped the flow of gas--that wasn't it.

Next the customer observed what appeard to be a hairline crack in the drain tube from the inside.  We took the bowl off and filled it with water, it didn't leak--that wasn't it.

Next we checked the float heights--they were all correct at 22mm--That wasn't it.

We then tried to lower the float a bit maybe because the float wasn't getting enough pressure.  Raising it to 24 mm stopped the leak.  Here's what I think happened:  These bikes are old and almost all of them have had the carbs into before.  Sometimes the composite float part can be off axis in relation to the rest of it.  For example, if you just held the everything where it was and then just rotated the axis of the float down (looking at it from upside down as if you were working on it) it would actually not be set correctly at 22mm.  Add to this other variables like the little adjustment tab being tweaked and you can have problems when initially everything looks to be set correctly. 

I hope I said that clearly enough and I hope that helps.

[quidger]

The needle valve does not screw in.  It has an o-ring on it and then it presses in.  On top of that is a little retainer clip with a screw.  Without the o-ring gas would leak out the sides.  It isn't precision pressed in or anything.

I actually posted a response to this before but for some reason it didn't post. 

I had a customer who this same problem despite everything appearing to be correct.

First we thought the valve was faulty and it was leaking.  We took the float bowl off and turned the gas on--when the float was raised the valve closed properly and stopped the flow of gas--that wasn't it.

Next the customer observed what appeard to be a hairline crack in the drain tube from the inside.  We took the bowl off and filled it with water, it didn't leak--that wasn't it.

Next we checked the float heights--they were all correct at 22mm--That wasn't it.

We then tried to lower the float a bit maybe because the float wasn't getting enough pressure.  Raising it to 24 mm stopped the leak.  Here's what I think happened:  These bikes are old and almost all of them have had the carbs into before.  Sometimes the composite float part can be off axis in relation to the rest of it.  For example, if you just held the everything where it was and then just rotated the axis of the float down (looking at it from upside down as if you were working on it) it would actually not be set correctly at 22mm.  Add to this other variables like the little adjustment tab being tweaked and you can have problems when initially everything looks to be set correctly. 

I hope I said that clearly enough and I hope that helps.

Very good explanation. Thanks for sharing your knowledge. I will look at all of the possible issues that have been commented on by all and see if I can solve my problem.

This is a great forum with a lot of very knowledgeable guys.

Thanks to all.

[Deltarider]

You haven't put the float needles in upside down, have you? Nah... not you.

[bollingball]

You haven't put the float needles in upside down, have you? Nah... not you.

Is that even possible?
Ken