Topic: Clear tube method. The EASY way and CHEAP

[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

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:

I understand the concept- I didn't say the routing or length of the tubing mattered(the side of the float bowl just seemed a logical place?) I was merely warning that if your tube moves after the bowl is full your level will move- ok given if you move it downwards the valve simply lets a little more fuel in and the reading remains correct, however if you pull the tube higher (after the bowl has filled) the level in the tube will rise giving you a false reading- as in some of the fuel from the tube flows back into the float bowl giving you a correct but slightly higher reading...

The four tube set up you pictured is awesome much easier than having to do them one at a time like I did!

[Black 750K8]

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".

You take the fuel line off BEFORE you drop the bowl. I do all my testing and adjustments on the bench with the carbs level side to side and front to back. I have PD42b carbs and the book calls for 14.5mm + - .5mm float height. With them set dead on 14.5mm and the fuel line off the clear tube shows 3mm below the gasket so now if I start having poor running conditions I can hook up a clear tube and get a damn good idea if the issue is enough fuel in the bowls. Then I start looking else where for problems with out taking the carbs off as a first thing to do. I may still have to take them apart but not right away.

[brewsky]

@ jonda500........

After re reading your post, I misunderestimated what you were saying!
You are correct that changing the volume in the tubes themselves can alter the readings.
I leave the tubes in place, and check during actual riding by stopping and letting the levels equalize while the engine is running.
Probably a little overkill, since the levels while riding are all over the place anyway

[Black 750K8]

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.

Is it so hard to just take the fuel inlet line off before taking off the bowl ? 

[FuZZie]

Nice research SohRon, I have the original shop manual and parts manual I've also a Chiltons guide Think I'll be shopping for a nice original copy of that Clymer's.

[jude0007]

This is an interesting post.  Ironically enough, I've got a 76 CB550K (which is what his original picture was) that fuel just pours out of the overflow tubes, all of them.  I've thoroughly cleaned the carbs, set float height correctly (had someone else verify correctly as well) got new float needles (NOS ones, not cheapies) and still overflows.  The bike was pretty hacked up when I got it so I worry that the carbs might not be the original to the bike or something else odd.

This will be a really good way for me to understand what's going on inside the carb bowl with minimal work.

[grcamna2]

What condition are your floats in ?

[flybox1]

a few things come to mind.....
1. verify the NOS float valves actually can shut off fuel flow when the floats are depressed.  its seat might be worn.
2. debris in the tank prevents a good seal between the float valve and its seat.
3. cracked overflow pipe allows fuel to drain no matter what.
4. floats are stuck in the down position. a few bumps of the carb bank with a rubber mallet might free them up. do this as you turn on the petcock.

others will chime in and add...

[jude0007]

a few things come to mind.....
1. verify the NOS float valves actually can shut off fuel flow when the floats are depressed.  its seat might be worn.
2. debris in the tank prevents a good seal between the float valve and its seat.
3. cracked overflow pipe allows fuel to drain no matter what.
4. floats are stuck in the down position. a few bumps of the carb bank with a rubber mallet might free them up. do this as you turn on the petcock.

others will chime in and add...

I'm thinking it's more along the lines of #1 as I've checked everything else.  Tank is clean, filter used, no cracked overfill (all 4 are doing it) and floats aren't stuck.  Also the floats are in good shape.

I need to verify that float needles are even capable of shutting fuel off.  What's weird is I think I checked it awhile ago with water and they help just fine, a few days later installed on the bike and problem persisted.  I've been working on like 4 bikes so I forget what I've done which may be half the problem.

Anyways, I don't need to hijack thread, just think this will be interesting to check.

Actually I came up with a better solution.  I just bought a Triumph Thruxton yesterday, fuel injected baby!!!! Still love my vintage bikes though...

[Bru-tom]

You take the fuel line off BEFORE you drop the bowl. I do all my testing and adjustments on the bench with the carbs level side to side and front to back. I have PD42b carbs and the book calls for 14.5mm + - .5mm float height. With them set dead on 14.5mm and the fuel line off the clear tube shows 3mm below the gasket so now if I start having poor running conditions I can hook up a clear tube and get a damn good idea if the issue is enough fuel in the bowls. Then I start looking else where for problems with out taking the carbs off as a first thing to do. I may still have to take them apart but not right away.

how do you get the fuel that is sitting on the float valve out without tipping the carbs? there is fuel sitting in the "T" piece that can also change the level somewhat? I guess its a negligible amount.

I would really like to test the tube method, i have already machined the brass float bowl inserts, just waiting for the oportune time, my bike is running too damn well at the moment

[lucky]

a few things come to mind.....
1. verify the NOS float valves actually can shut off fuel flow when the floats are depressed.  its seat might be worn.
2. debris in the tank prevents a good seal between the float valve and its seat.
3. cracked overflow pipe allows fuel to drain no matter what.
4. floats are stuck in the down position. a few bumps of the carb bank with a rubber mallet might free them up. do this as you turn on the petcock.

others will chime in and add...

Also check to see if the float bowl overflow tube has a vertical crack in the tube.
This is common in colder climates.
You will have to use a magnifying glass to see the crack.
You can solder the crack after cleaning the brass.

[AintNoEasyWay]

Could someone point me in the direction of a thread or write-up with a full explanation of how to do the clear tube method? I've got a general idea of what we're doing here, but not sure how I would do it for my K7 (PD41a carbs). Would like to use this to double check my float height instead of taking the carbs back off.

[Stev-o]

This is turning into an oil or pod vs airbox thread for fukcs sake...

Popcorn anyone?!

[lucky]

Could someone point me in the direction of a thread or write-up with a full explanation of how to do the clear tube method? I've got a general idea of what we're doing here, but not sure how I would do it for my K7 (PD41a carbs). Would like to use this to double check my float height instead of taking the carbs back off.

It is ironic that your screen name is " AintNoEasyWay"because all you need to do is buck up bucky and remove those carbs and set the float levels by measuring them.
Also if the float needles have not been renewed for many years, it is time.


Think about this: Even if the "clear tube method reveals that the levels are way off, you still will need to remove the carbs to replace the float needles and seats.

You cannot just adjust them.
They may have big differences because the float needles are worn out.

When the float needles are new and in adjustment nothing can change that. Al that can happen is that the needles get worn out.
The fact that the levels are off is an indication that something IS wrong with the float needles.

[lucky]

This is turning into an oil or pod vs airbox thread for fukcs sake...

Popcorn anyone?!

I agree Stev-o but no mechanics that I have known during my life have ever used this "clear tube method", all we ever did is replace float needles, set them by the book with a measuring device and we never got any come backs.

[750K]

This is turning into an oil or pod vs airbox thread for fukcs sake...

Popcorn anyone?!

Can I use the clear tube method to check the canola oil level in my popcorn popper Stev-O? I measured the oil with my measuring cup but I think I should still check it with the clear tube method, any opinions?

[BobbyR]

OK, the clear tube method works. It is very easy on the 750s since the drain is at the bottom. There are some things to remember.

1. It is not meant for initial adjustment, it is a quick check to see if you have a bowl that is high or low on the bike. That is all.

2. It should be done on the centerstand so the carbs are as level as possible.

3. Cracks in the overflow tube will mimic a flooding carb, bad seal on the drain screw. The overflow tube and the drain use the same hose barb at the bottom of the bowl. So, it is hard to tell the actual cause without examination.

4. If you have gas leaking out of the bottom drain, you can use the clear tube to see if the carb is flooded.  If it is not, you have a poor sealing drain screw or cracked tube. You take that bowl off and you fix it.

5. As Lucky says you can solder the brass tube crack. People use JB Weld. Solder is best since it does not react quickly with gasoline.

6. There are many bad ways to do things on these bike. There are also several good ways. You pick the one that you feel you can accomplish given your time, skill level and facilities. 

[flybox1]

This is turning into an oil or pod vs airbox thread for fukcs sake...

Popcorn anyone?!

Can I use the clear tube method to check the canola oil level in my popcorn popper Stev-O? I measured the oil with my measuring cup but I think I should still check it with the clear tube method, any opinions?

NO, YOU CANT!
It doesn't work that way and never will.  You have to follow the directions in the cookbook.
I worked at a movie theater as a popcorn popper.  I should know. 

[TwoTired]

Could someone point me in the direction of a thread or write-up with a full explanation of how to do the clear tube method? I've got a general idea of what we're doing here, but not sure how I would do it for my K7 (PD41a carbs). Would like to use this to double check my float height instead of taking the carbs back off.

The PD carbs are easy.  Remove the bottom drain tube and replace it with a clear fuel resistant tube.  Route the tube up the side of the bowl, using enough to reach well above the gasket interface.  Now simply turn the carb bowl drain tube until the clear tube fills.  The fuel level in the clear tube will rise to the same level inside the carb bowl.  You will need to have the fuel petcock on and the carbs level with earth's surface for a true representation, just like the dipstick in your oil supply.

Or, you can listen to deep pockets lucky and pay dealer prices for time and parts to replace everything on your bike.  Your choice.

[AintNoEasyWay]

Ahaha. /endthread.

[grcamna2]

That is one Hungry popcorn eater you found there 

[Stev-o]

This is turning into an oil or pod vs airbox thread for fukcs sake...

Popcorn anyone?!

Can I use the clear tube method to check the canola oil level in my popcorn popper Stev-O? I measured the oil with my measuring cup but I think I should still check it with the clear tube method, any opinions?

NO, YOU CANT!
It doesn't work that way and never will.  You have to follow the directions in the cookbook.
I worked at a movie theater as a popcorn popper.  I should know. 

Not so fast Fly. I read it on the internet so it has to be true!
Plus everyone knows that most theaters use coconut oil for their popcorn!

[Drummer]

You know you can angle your head 5 different ways and get 5 different levels when looking at that hose.
Seems the way to go to me is be METICULOUS when have them out for overhaul. Most float problems are caused by damaged needle or seats or just dirt. Float level is important but other things vastly effect a carb's operation. Seems like a lot of trouble for little value. If one overflows one time don't panic it's probably dirt. Try to run it dry. Sometimes that will clear it out.
JMO

[PeWe]

The clear tube is for diagnose, acknowledge flooding carbs. No meaning to try other pilot jets then. What to do next when carbs are flooding can be different. Adjust the floats OR clean valves OR check if floats are stucked/not moving free OR valves are bad OR.....

Anyway the tube method IS a good way to find correct diagnose.
I had done all those other stuff before adjusting the floats to better level and engine ran much better.

[Bankerdanny]

So, to resurect this thread...

I have a K2. I want to do float clear tube test. My drain screw is the larger type that has no nipple. My overflow pipe is the nipple on bottom.

How do I connect clear tubing to the drain screw? When I open the drain screw, fuel starts to leak out obviously however it doesn't flow through the overflow pipe (mine is clear so I can see that its not  overflowing).

I dont see how I can connect tubing to a non-nipple drain. Help?

While the clear tube method gets a lot of press, reality is that it is a pain in the ass for every version of the SOHC4 except the last couple years of 550 and 750 with PD carbs.

I would make an adapter with spare bowl drain screws.

Buy extra float bowl drain screws and drill a 1/8 inch hole though the center (I would start from the bowl end since there is already a hole there). Find yourself some brass tube that can fit snuggly inside of some small diameter clear tube. The brass tube should be larger than the size of the hole you drilled through the screw, but not a lot. Then drill a shallow hole large enough for the brass tube to fit into. Don't drill too deep because you don't want to drill off the top of the bowl drain. Attach the brass tube to the screw with some 2 part JB Weld. Then when you want to verify the fuel level you start with empty bowls. Install the drain screw adapters and tubes, then turn the fuel on and see how high the level gets.

Sometimes you can find clear tube that fits snuggly in the drain screw port by itself, but I have found that is a recipe for a mess. Whatever method you settle on, you always need to start with empty bowls.