Topic: Clear tube method. The EASY way and CHEAP

[KeithB]

I think some confusion is because not all carbs drain through the overflow.

I have read the whole post and this statement just doesn't sound right.
How can ANY carb drain through an OVERFLOW tube?
Anyway...
This "clear tube " method looks like a good way to double check float levels.
Obviously, the clear tube doesn't connect to the barbs under the carbs of the CB Hondas as these are overflow tubes and if you get gas from them, something is wrong.
So, if I understand correctly, you have to make a fitting to go on the drain plug hole.
Pics anyone?

[goldarrow]

I think some confusion is because not all carbs drain through the overflow.

I have read the whole post and this statement just doesn't sound right.
How can ANY carb drain through an OVERFLOW tube?

PD carbs

I think some confusion is because not all carbs drain through the overflow.

So, if I understand correctly, you have to make a fitting to go on the drain plug hole.
Pics anyone?

pics in first post.  remove the drain screw and the T plugs right into the carb drain hole

[Tugboat]

^PD carbs share drain & overflow. Backing out the drain screw a bit allows fuel to drain through the overflow, as opposed to the hole where the drain screw is. If you saw the bowl it would make sense.

[flybox1]

^PD carbs share drain & overflow. Backing out the drain screw a bit allows fuel to drain through the overflow, as opposed to the hole where the drain screw is. If you saw the bowl it would make sense.

+1
the tip of the drain screw, when fully seated, blocks fuel from flowing out the drain tube.

[goldarrow]

NO... this method is not correct, and it will not run right.
You must measure the float height.
You can only use the "clear tube method AFTER you have set the float height by measuring.

BINGO!

[754]

This may help. Get a mikuni 8 shaped tab that holds the overflowed with tube from flapping.. Would hold your SIGHT TUBE nicely while performing this trick.

[lucky]

Lucky, the goal is FUEL LEVEL, right? Too much or too little the bike will not run correctly.  I know we can agree on this.
By setting the float height, by the book, you are assuming you set them correct AND the floats are operating correctly. Nothing wrong with this method, but, once you put the bowls back on, the clear tube method is the only way to ensure the fuel level is correct.   
We are just double checking our work here, nothing more.

There is nothing wrong with checking your work but here is the problem:
Everyone has a different answer as to what the float level should be.
Some say the level should be at the interface of the float bowl and carb body. That cannot be right because then the fuel will be higher than the overflow tube in the float bowl.

Some say the level should be 2mm below the interface of the float bowl and carb body.  That may not be right either because there is no book that gives you the float level that way. Some say 4mm??? Makes no sense.

When the motorcycle is on the side stand and the flloat level is too high and you put the bike on the side stand then carbs on the left side of the bike could overflow and carbs 1 and 2 are connected with carbs 3 and 4.

IF you check a perfectly good bike (on the center stand) and you remove a float bowl (kind with the clip on bowl for FAST removal), you will notice that the float bowl is about a little over half full. But anytime you remove a float bowl the float immediately drops allowing more fuel to run into the float bowl ruining any chance to see what was really going on. Remember some allowance has to be made for fuel sloshing n you stop and accelerate. That is why the top of the float bowl overflow tube is rounded over to help that sloshing problem. Otherwise the float bowls could be running over all of the time.

Mechanics always just measured the float level and made sure the float is new, and don't worry about it anymore.


Cleaning a float needle seat with toothpaste is also not going to fix a seat that is damaged from an old float needle thats been vibrating around for two years.

If you want your engine to run right just replace the float needles and seats.
If it is a rubber tip needle then just replace the float needle and make sure the seat is clean.

Look at any set of float needles and you will see with a magnifying glass that the shiny ring on the tip of the float needle is really a step worn into the needle from vibration. That is WHY Honda changed to rubber tip float needles. But the rubber tip needles have problems too. The rubber tip float needles and metal needles are NOT interchangeable. They are different angles.

Just because a engine is not running right does not mean that it is not getting enough fuel. Anytime someone is working on a car for instance and a passerby says "Sounds like it is not getting enough fuel." That is like Muddy Waters saying" My phone is ringing,sounds like a long distance call. LOL....lol

[lucky]

Another reason why I love this forum. A great exchange of ideas.

The float bowl fuel in the picture is right on the money. The fule should be just under the gaslet. It may be the camera angle, but the carb looks a little tilted. You really want the carb as lavel as possible.

Lucky is a purist and a zealot. That does not mean he is wrong, it also doesn't mean he has the best procedures either.

I am not a purist and a zealot. I do not engage in name calling either.

Even the Kawasaki 1500 which uses a 40 mm carb has a section in the Clymers workshop manual and it explains why the use of the"clear tube method" should not be used unless the tube is an exact length. It shows why this method may not work as intended.
That method does have problems.

If you really want to find out, take a float bowl off of a motorcycle and do the clear tube method on a workbench. The problem is that the float bowl contains a large amount of fluid compared to what is in the clear tube.  If it was JUST a tube then it would be less problematic. As you raise the tube up or down you will get different results.

Like I said, the gas in the float bowl CANNOT be above the overflow tube in the float bowl and the interface of the float bowl and the carb body is ABOVE that pick up tube. So that cannot be right.

This "clear tube method" Was never used when the CB750 was in its heyday. NEVER.

The only time I have seen or heard of it is on this forum.

[lucky]

Think about this:

If you had a new float needle and seat and you measured the float height as described in the book and photos, THEN you put it back together and measured the level of the fuel with a "Clear tube method" and the level was lower that the top edge of the float bowl, which one is right?? See what I mean?


But you KNOW that the fuel is not supposed to be OVER the top of the overflow tube in the float bowl right???


If a Honda came into my shop and the bike is on the center stand and I remove the float bowl and it is completely filled to the top edge I would KNOW something is wrong.
I would have to adjust or replace the float needle and seat.


I have the advantage.
I am old enough that I actually did work in a Honda Dealership when these bikes and all the other Hondas were introduced and have removed MANY float bowls.
I know what a normal float bowl level looks like. And it is not supposed to be full to the top edge or even close.

[Bru-tom]

If a Honda came into my shop and the bike is on the center stand and I remove the float bowl and it is completely filled to the top edge I would KNOW something is wrong.
I would have to adjust or replace the float needle and seat.

i gave this some thought as a way of testing/seeing what the level is in my float bowls. But this will in fact not work. The level will always be higher than it actually is because as you drop the float bowl off the carb body, the float will drop opening the float valve and the residual fuel in the fuel line from petcock that is sitting right at the float needle and seat will empty into the float bowl increasing the level to a now "incorrect reading".

[Black 750K8]

He may have a valid point, not everyone reading the site may understand it's for double checking.

He is the one that doesn't understand  it's for double checking.

[TwoTired]

If you really want to find out, take a float bowl off of a motorcycle and do the clear tube method on a workbench. The problem is that the float bowl contains a large amount of fluid compared to what is in the clear tube.  If it was JUST a tube then it would be less problematic. As you raise the tube up or down you will get different results.

This is wrong, and defies the laws of gravity and physics.

You should actually try this yourself to prove it wrong, rather than blather incorrect theory.


If you fill a tub does water stand higher at one end than the other?  No, it doesn't fluid is self leveling.  Raise the sight tube higher and the fluid level will drop to whatever level is inside the bowl.

Sight gauges have been used for this very purpose (to tell the level of fluid inside a reservoir) for over a century.

Isn't it nice to tell someone to buy parts (that could be repaired) out of his pocket rather than yours?  No hardship for you.  Just a few extraneous keystrokes.

Think about this:

If you had a new float needle and seat and you measured the float height as described in the book and photos, THEN you put it back together and measured the level of the fuel with a "Clear tube method" and the level was lower that the top edge of the float bowl, which one is right?? See what I mean?

Damn funny you asking others to think.

If you used original spec Keihin parts, you wouldn't need the clear tube method in an totally stock bike.  Because, Honda never expected their service tech guys to have any analytical skills.  Just replace parts at customer expense, 'til it stopped customer complaining.
If you used aftermarket parts not made to original specs. (such as stiffer spring pins in the float valves), even a stodgy Honda technician wouldn't get the machine to run properly.

I have the advantage.

I am old enough that I actually did work in a Honda Dealership when these bikes and all the other Hondas were introduced and have removed MANY float bowls.
I know what a normal float bowl level looks like. And it is not supposed to be full to the top edge or even close.

I disagree.  You have brain washing, and wrote memory from repetitive tasks requiring no analysis of how the machine actually works.  And, years and years of replacing parts at customer expense, whether it was actually needed it or not.

I do agree that the actual level of the fuel in the installed bowl with the bike upright and level should be about 3-4mm below the bowl gasket line in a normal instance.  However, in fine tuning for inlet and exhaust mods., the level can be reduced to lean an overall rich condition.

[FuZZie]

If you really want to find out, take a float bowl off of a motorcycle and do the clear tube method on a workbench. The problem is that the float bowl contains a large amount of fluid compared to what is in the clear tube.  If it was JUST a tube then it would be less problematic. As you raise the tube up or down you will get different results.

Damn TT saved me the speech! 
Using a bucket full of water on one end of a water level improves it's performance, quick read explaining using a water level he also explains the pitfalls.
http://www.glacierboats.com/tongass/waterlevel.html

[754]

The only way a bowl could. Be even near full is if the Float were MISSING.

[alacrity]

I prefer to think of my float bowl as 7/8 full as opposed to 1/8 empty (give or take).  This probably makes an optimist.

[flybox1]

If you really want to find out, take a float bowl off of a motorcycle and do the clear tube method on a workbench. The problem is that the float bowl contains a large amount of fluid compared to what is in the clear tube.  If it was JUST a tube then it would be less problematic. As you raise the tube up or down you will get different results.

Damn TT saved me the speech! 
Using a bucket full of water on one end of a water level improves it's performance, quick read explaining using a water level he also explains the pitfalls.
http://www.glacierboats.com/tongass/waterlevel.html

Haha, yeah...I got half of a response written and then said eff-it.  No point.
Lucky knows he's right, and that won't change...
TT...always appreciate your well written responses.

[SohRon]

This "clear tube method" Was never used when the CB750 was in its heyday. NEVER.
The only time I have seen or heard of it is on this forum.

From the Clymer's CB550 shop manual, section six, Pages 108-109 (click to enlarge):



This has been in all of the Clymer's CB550 books from the '70s until now; It's how I learned the procedure.

[lucky]

If a Honda came into my shop and the bike is on the center stand and I remove the float bowl and it is completely filled to the top edge I would KNOW something is wrong.
I would have to adjust or replace the float needle and seat.

i gave this some thought as a way of testing/seeing what the level is in my float bowls. But this will in fact not work. The level will always be higher than it actually is because as you drop the float bowl off the carb body, the float will drop opening the float valve and the residual fuel in the fuel line from petcock that is sitting right at the float needle and seat will empty into the float bowl increasing the level to a now "incorrect reading".

Stated very clearly. That has been my experience.

[lucky]

This "clear tube method" Was never used when the CB750 was in its heyday. NEVER.
The only time I have seen or heard of it is on this forum.

From the Clymer's CB550 shop manual, section six, Pages 108-109 (click to enlarge):



This has been in all of the Clymer's CB550 books from the '70s until now; It's how I learned the procedure.

Go back to Step#9 on that page.
IT does NOT tell you what the level is supposed to be.

On another page in that same book it says:
Measure the float height FIRST, BEFORE using the clear tube method.


A correct float height must first be set by measuring.

[750K]

This is turning into an oil or pod vs airbox thread for #$%*s sake...

[Spanner 1]

Have to agree , 40 yrs. after these bikes were made and all the aftermarket floats, float valves  ( metal tipped and rubber tipped ), clear tube float level method was never more accurate to confirm the bowls have the correct fuel levels in them.... no so much the Honda float level specs.... I'm all about 3-4mm below the bowl gasket= correct 

[grcamna2]

Those are nice diagrams.

[jonda500]

For the clear tube method to work accurately you must attach(tape) the clear tube securely to the bowl side so that it remains completely stationary when you turn the fuel on - the length of the tube from the drain screw to the top of the bowl(fuel level) must not change after the bowl fills or your reading will be wrong

[mrbreeze]

Last time I checked my levels was around 5 years ago after I rebuilt my carbs. I set my float levels according to the book and although I hadn't vac synched yet, the bike ran way better just from having clean rebuilt carbs with nice clear passageways and spotless jets. You have to do a bench sync first to get you in the ballfield like you have to measure the float height. Lucky.....we know you have to measure float height first but it sounds to me and everyone else here that you think you just measure float height button it up and go. The clear tube method shows you the actual level in the bowl. If you just bench sync your carbs and go....it may run but it ain't gonna be right. Thats why we vac sync at the end. then we know they are all on the same page. Clear tube method lets you know that all fuel levels in the bowls are on the same page. I dunno...............maybe you have Xray vision and can see that they are all level right through the metal fuel bowls!!!! Also...........my levels were all acceptable except #3 was quite a bit lower so I had to pull that bowl and readjust the float to match it to the others. I don't recall the exact fuel level measurement but it is just a shade below the body/bowl joint.

[brewsky]

For the clear tube method to work accurately you must attach(tape) the clear tube securely to the bowl side so that it remains completely stationary when you turn the fuel on - the length of the tube from the drain screw to the top of the bowl(fuel level) must not change after the bowl fills or your reading will be wrong

You seem to be missing the concept.

It doesn't make any difference how long or where the tubes are, the level in the tube will be the same as the bowl (if you leave the petcock on, which should be done to allow the levels to equalize).

If you want to check the level of each carb to other carbs, it doesn't matter where the tubes are as long as the bike is level. Put the 4 tubes together and you can easily see any relative difference.

If you just want to see the level relative to a mark or reference on an individual bowl, then, naturally, it needs to be close to the carb as you show.

To show it both ways, route all 4 tubes together against one carb: