Topic: Carbs $uck

[Magilla]

Man the carbs on these bikes suck.  They are so temperamental. It's  what you would expect on a race motor and not a daily driver.  Case in point;

I have been working on my carbs for weeks now.  Learning as I go.  I understand that while I am learning I will have to do things over and over until I get it right.  It's part of learning.

The problem I am having is with the overflow.  I have pulled each one apart, cleaned it and set the float.  I've done it no less than six times per carb.  When I put it back together, it does not leak.  Then after an hour or a day or a few days one will start to overflow.  I pull it apart, check everything, put it back together and no leak.  Then a different carb will leak.  Maybe not today but for sure it will overflow.

I have replaced all of the float needles and inserts with new non rubber tipped ones.  Today was the day it was going to be all better.  Then I turned the gas on.  Carb 3 started to overflow.  I pulped it apart rechecked the float level, checked to see if it shut the gas off when it was floating and put it back together.  I turned the gas on and after a short wait carb 1 started to overflow.  Fixed it and then #2 started in.  Fixed it and then #4 started to overflow.

All four gave me fits today.  What the hell.  I did notice on carb 1 that the float has room to move from side to side and if it moves far enough to the left it will hang up on the housing of the carb.

After resetting everything I took the bike for a nice ride today and it ran great.  No overflow issues but then again it only seems to happen when it's sitting and not when it's running.

Will this week be my first week without a gas spill?  I think I leak more than I use.

[Dimitri13]

When you turn on the fuel and one starts to overflow, turn off the fuel then tap the carbs with the end of a screwdriver.

[LesterPiglet]

Are you sure you don't have crap in the tank? Particles could be blocking the float valves.
I've also read lately another members fuel line was breaking down and sending tiny pieces of rubber into  the carbs.

[ekpent]

What year are the carbs or bike again and is it a 750. Never seen rubber tipped needles in the 69-76 750's if that is what you have. Also some aftermarket gaskets can protrude into the bowl and cause problems with floats. Sounds like the float needle ends are not meshing well with the seats,maybe some lapping would help unless the parts are to far off to be really compatible. How much aftermarket stuff is in there ?  Turning off the gas at petcock is also advisable when not in use.

[lucky]

Something is wrong.

If you just put in new floats AND SEATS and adjust the float levels properly you will not have problems.

Things that can go wrong.

You put a metal needle in a seat intended for a rubber tipped float needle.
You bought USED float needles and seats off of Ebay and paid full retail plus shipping.
You try to save money by using a used seat or needle that has been polished.
You buy new metal needles and put them in USED seats.
Someone tells you the float needles are good put they were just polished and were not new. Stuff like that.

You adjusted the floats with a plastic tube so that the level of the gas was 2mm from the top edge of the float bowl... INSTEAD of what the factory setting is supposed to be..

You have junk in the gas tank that is getting through the filter.
You have water or moisture in your fuel, or in the bottom of the tank.

ASk YOURSELF this question:

If you were a dealership mechanic and a customer had a bike with this same problem what would you do ?
Your reputation is at stake.

A. Just polish the seat and put in the used needle.
B. Put a rubber tip needle in a seat made for a metal needle.
C. Just clean the metal needle and the seat and put it back together.
D.  Check the gas coming out of the tank in a glass jar, and then put in brand new   seats and needles for that year bike and set the floats according to the factory manual.

[harisuluv]

What do you have the floats set at?  Should be 26mm for the earlier 750s if that is what you even have since you haven't really told us much about the bike.

Are you measuing from the lip of the carb where the two indents are on each side?  If not you will be too far down and you could leak.

Something a lot of people miss is that they have distorted floats.  What I mean by that is that the axis of the float is not perpendicular to the rest of it, if that makes sense.  If they are bent then when you are at the right setting things will be a little off.  Like your float adjustment will be way too high. 

[trueblue]

By the randomness of how it is happening, my guess is you need to clean your tank, there has to be something holding the float valves open, when you drop the bowl it is allowed to move from under the valve and allow it to seal.

[Magilla]

The bike:  1976 CB750. Stock everything.

I am not replacing rubber tip floats with metal tip float.  Originals we're metal.  New ones are metal.

Not using used parts.  Brand new items bought.

No, I repeat no sediment in the tank.  I have replaced the tank with one that is perfect inside.  I have also drained Gas into a glass several times just to be sure.  It's got clean gas.

Float levels set to 26

It just seems that sometimes the floats don't float to the top.  I think that the float just barely hits the housing of the carb.  They all have a small chamfer on them from the factory.  I believe this is a slight design flaw and that the chamfer should be a little bigger.  It would not effect the ability to float because it is above the gas BUT it would eliminate the ability to get stuck on the housing.

This theory also fits well with the "hit it with a screwdriver" fix.

[DJ_AX]

I recall reading a snippet somewhere that explained how after many years (like almost 40) the edge of the float will wear on the posts that the pin is in... causing it to hang up! I think it was from an excerpt of HondaMans Book...  (I gotta get that)

[Magilla]

I never seem to have the problem when it is running so it seems as though the vibration of the motor is keeping the floats from sticking.  Of course now that I put that out there, they will leak like the Titanic the next time I start it up!

Currently I don't have the overflow tubes hooked up.  I have two reasons for that.  The first is so I can quickly tell which carb is overflowing and the second is just in case it happens when its running I don't want it spilling on my rear tire.  That would be bad.

If anyone ever needs the floats changed or the jets replaced, just let me know.  I have done it so many time recently that I think I could do it in my sleep.

[iron_worker]

The overflow tubes are put in place to direct the fuel away from the hot engine cases to prevent fire which is also bad!

[Greggo]

May want to check that all four floats are actually floating, and not letting gas in...it would weigh them down, keeping them from floating high enough to close the valve.  Just a thought.

[lrutt]

I have to say, I've had my K6 since 1978 and I can only recall having the carbs off twice in all those years, and I can't remember the last time as it's been so long. I've never put any kind of kit in them. the ONLY thing I did was add an inline fuel filter WAAAAAYYYYY back in the early 80's.

What a horrible unreliable POS, don't know why I've kept it all these years

[lucky]

May want to check that all four floats are actually floating, and not letting gas in...it would weigh them down, keeping them from floating high enough to close the valve.  Just a thought.

The last time I saw floats that were bad was when they were made out of cork with shellac painted on em from the Honda Factory.

[lucky]

It sounds like you have done all of the right things.
In your original post you reported that all FOUR carbs have overflowed after stopping one of the other three from overflowing.

When you put the bike on its kickstand  it is possible just a little gas could leak out because remember that if all of the float bowls are full then you lean the bike over on the kickstand just the movement of the bike can cause the gas to slosh and spill over a small amount. NOW if the overflow tubes are installed and are the right length to go over board behind the engine as in the stock configuration that a very small amount of gas can go out but it would evaporate.

Also I have brand new CLEAR plastic tubing on my overflow tubes and occasionally i will see a small amount of gas inside the tube  it just seems to hang inside the tube where it lays flat on the top of the engine. It does not flow out.
I have actually tried to lift up the clear tube and make the gas flow out all the way onto the ground but it does not.

I am now starting to think that maybe all FOUR of your carbs have float levels that are too high??
But the only way that could be possible is if the method you are using to check the float level is incorrect. And there is no way to know how you did that.

And I also assume your carb float bowl vent tubes are installed and are
functional?

Floats can get hung up occasionally but not very often.
If you look carefully at the intersection of the brass part of the float where the pin goes through the aluminum posts that the pin goes through,  you will see why it is almost not possible for the float to get hung up.

[bollingball]

Quote from LuckyYou adjusted the floats with a plastic tube so that the level of the gas was 2mm from the top edge of the float bowl... INSTEAD of what the factory setting is supposed to be..

Once you measure and set a float then if you fill the bowl and remove it to see where it filled to then there is no reason you can not use this level with the clear tube method from then on. Also it is a lot easier to check with out having to remove the bowls. Just like having a clear bowl.
 Do you want to explain why not?
 Where did you come up with the 2mm and what carb was this for?
 Do you even know or care how much fuel is in your bowls?
 On my carbs it is just a simple matter of using a clear tube for my drain/overflow hose they stay on there all the time. So if I suspect a fuel problem I just hold it up next to the carb and open the drain screw then I know where my fuel level is But now you say take off the carb then take off the bowl and measure the float That is the way the factory says to do it.
Ken

[Greggo]

May want to check that all four floats are actually floating, and not letting gas in...it would weigh them down, keeping them from floating high enough to close the valve.  Just a thought.

The last time I saw floats that were bad was when they were made out of cork with shellac painted on em from the Honda Factory.

That's nice Lucky.  But, I've seen brass floats go bad, and I bet I'm not the only one

[lucky]

Quote from LuckyYou adjusted the floats with a plastic tube so that the level of the gas was 2mm from the top edge of the float bowl... INSTEAD of what the factory setting is supposed to be..

Once you measure and set a float then if you fill the bowl and remove it to see where it filled to then there is no reason you can not use this level with the clear tube method from then on. Also it is a lot easier to check with out having to remove the bowls. Just like having a clear bowl.
 Do you want to explain why not?
 Where did you come up with the 2mm and what carb was this for?
 Do you even know or care how much fuel is in your bowls?
 On my carbs it is just a simple matter of using a clear tube for my drain/overflow hose they stay on there all the time. So if I suspect a fuel problem I just hold it up next to the carb and open the drain screw then I know where my fuel level is But now you say take off the carb then take off the bowl and measure the float That is the way the factory says to do it.
Ken

I will explain why that method may not be correct.
It is possible to get that method to work but there are problems.

When you set the floats with a float gauge or measuring device, You are setting the level of the top of the plastic or brass float part. That has nothing to do with the actual level of the gas inside the float bowl.

Lets assume that you set the floats the correct way with a float gauge or a steel ruler then let the float bowl fill with gas. Then if you shut the gas off and removed the fuel line from the carbs to eliminate the fuel in the line from letting that gas into the float bowl while you are removing the float bowl to actually see how much gas is in the float bowl, then knowing where to make the mark for the gas level so you can use your clear plastic tube method. I have not heard anyone on any forum say that they did that. Matter of fact many say the level of the gas should be 2mm from the top edge of the bowl. Where do they get that measurement and why is it always an even number?
Also 2mm is only about .80 thousandths. That is just slightly more that 1/16 inch below the top edge of the float bowl. That is way too much!

I can tell you from experience from working on many carbs that if  you walk up to a motorcycle and just remove the float bowl on a  maintained and well kept
Honda that the float bowl will be about 3/4 full.


As far as that clear tube method of checking the level of the gas in the float bowl,
in some Honda manuals on some of their bikes, Honda even warns that when that method IS given, that the length of the plastic tube is critical for a correct reading.

[lucky]

May want to check that all four floats are actually floating, and not letting gas in...it would weigh them down, keeping them from floating high enough to close the valve.  Just a thought.

The last time I saw floats that were bad was when they were made out of cork with shellac painted on em from the Honda Factory.

That's nice Lucky.  But, I've seen brass floats go bad, and I bet I'm not the only one

Yes that is true.
But it is rare and usually the person immediately finds out when they remove the float that the extra weight and sloshing gas alerts them to the fact that there is gas inside the float. They do not even need to see if it will float. They can hear the gas sloshing inside the float.

The OP of this thread has taken his carbs off more than once and would have discovered that. But he said all 4 carbs leak at times so we can rule out all FOUR float being bad unless they were sabatoged.

[LesterPiglet]

Aha, tubes that defy the laws of physics.

[lucky]

Aha, tubes that defy the laws of physics.

The laws of physics are not all visible.
If you go to a library or good Honda shop and look in the Honda workshop manual for the Honda VF1000R, It talks about that method and warns the mechanic that if the correct length of the tube is not used that the reslts can be way off!
It shows a photo. I mention that because that VF1000R came way after the CB750. They learned from their mistakes.

 The length of that tube is important for that short length and the reason is that the float bowl has air in it. When the gas goes into the float bowl that trapped air can cause the level to be higher inside the tube.

I am not saying that method CANNOT be used, but at least you will have to determine  what the correct level should be in the float bowl, and I have not heard ONE person on this forum say how they determined that level. not one. And I doubt it would be an even number like 2mm exactly.

[LesterPiglet]

I don't think that measurement is terribly critical anyway. As long as the fuel level is a few mm above the main jet that should suffice.

Oh, could someone kindly post a picture of this clear tube attached to drain screws please. I don't understand how you can have tubes and screws in the same hole at the same time.

[lucky]

On page 60 of the Clymers manual it shows a tube being used to look at the float level and then suggests scribing a mark on the float bowl to be used for future reference.

BUT...It says to go to chapter SIX FIRST and set the float level with a float gauge and shows HOW TO DO THAT THE CORRECT WAY. Figure 13 bottom of page 125.

And if you LOOK at that drawing the scribed LINE is NOT 2mm below the top edge of the float bowl.
See what I mean ?

[bollingball]

Lester these are 78 pd42b carbs. This drain/overflow was a unique setup.
Click on pic.
Ken
edit I just noticed these carbs are empty

[LesterPiglet]

Ahhh thanks Ken. I've never seen those carbs before, hence confusion.