Topic: Fuel level in float bowl

[tlbranth]

I'm messing with the carbs ('70 CB750). I have the carbs on a wood rack on the bench and I'm doing a clear-tube level test. I set #1 with the float adjusting tool. I rechecked that setting by holding the tool in place with fuel on and watched that the fuel stopped and started flowing at the correct height. But when I put everything together and turn on the fuel (I'm using kerosene for the test), the fuel only rises to about 20mm from the carb body (where the float setting tool registers). It seems to me that when I've done this before, the fuel level was pretty close to the top of the bowl - but I can't remember much of anything these days.
There's no data I can find on actual fuel height, only float settings, that I can find. Can anyone provide that number? If not, a ball park (top of bowl, middle of bowl......
So far, this test is not filling me with confidence.

[flybox1]

Hondaman helped me sort out some issues with fuel level in my 350F bowls years ago.
It was his suggestion that all factory float settings achieved a fuel level in the bowls @ 3mm below the top of the bowl.
 

[700504]

Your float could be kinked and hanging up on the sides of the bowl, make sure to check that.

[markreimer]

I just did this with my k4 and had the same problem. There seemed to be some resistance or something with the fluid in the lines. If I took the bowl off, I could fill the bowl right to the brim yet the clear tube would still be 10mm down or so. Defies physics! I couldn't get it to work reliably so I went back to the conventional ruler method


Sent from my iPhone using Tapatalk

[Jimray23]

I'm messing with the carbs ('70 CB750). I have the carbs on a wood rack on the bench and I'm doing a clear-tube level test. I set #1 with the float adjusting tool. I rechecked that setting by holding the tool in place with fuel on and watched that the fuel stopped and started flowing at the correct height. But when I put everything together and turn on the fuel (I'm using kerosene for the test), the fuel only rises to about 20mm from the carb body (where the float setting tool registers). It seems to me that when I've done this before, the fuel level was pretty close to the top of the bowl - but I can't remember much of anything these days.
There's no data I can find on actual fuel height, only float settings, that I can find. Can anyone provide that number? If not, a ball park (top of bowl, middle of bowl......
So far, this test is not filling me with confidence.

How are you connecting the clear tubes?

--------------------------------------------------
Jim
1979 kz1000b ltd
    stage 3 cams
    pod air filters
    4-1 open exhaust(no muffler)
    full rewire
    dyna-s ignition
    dyna 3 ohm coils

[DaveBarbier]

Sometimes an air bubble can get caught in the line right where it enters the bowl. I flick it and sometimes I see a bubble start to appear and with more flicking it rises up the tube. I've also sucked a tiny bit to draw fuel up the tube. Just don't drink the fuel. Bike gets gas, I get bourbon.

I would LOVE if someone made fuel resistant clear plastic bowls. Could even be a clear plastic cup that you hold in place with rubber bands or tape. Doesn't matter the size and shape of the cup as long as the float moves freely. Yes, the clear tube method works, but this would be pretty cool.


Sent from my iPhone using Tapatalk

[BobbyR]

If you get the clear tubes working the rule of thumb is: the fuel level should be no higher or lower than the lower edge of the float bowl lip. This will keep the bowl gasket from being immersed in gasoline. Of course on turns there will be brief contact. The tube should be held against the float bowls, I found I can influence the heigt of the fuel in the tube by moving the tube away from the bowl.   

[DaveBarbier]

If you get the clear tubes working the rule of thumb is: the fuel level should be no higher or lower than the lower edge of the float bowl lip. This will keep the bowl gasket from being immersed in gasoline. Of course on turns there will be brief contact. The tube should be held against the float bowls, I found I can influence the heigt of the fuel in the tube by moving the tube away from the bowl.   

Theoretically, since motorcycles lean in turns the fuel should always stay level in relation to the float bowls. Obviously this doesn't happen in practice because of vibration and changing of speed, but hey, I'm just pointing out the physics.

[evinrude7]

If you get the clear tubes working the rule of thumb is: the fuel level should be no higher or lower than the lower edge of the float bowl lip. This will keep the bowl gasket from being immersed in gasoline. Of course on turns there will be brief contact. The tube should be held against the float bowls, I found I can influence the heigt of the fuel in the tube by moving the tube away from the bowl.   

Theoretically, since motorcycles lean in turns the fuel should always stay level in relation to the float bowls. Obviously this doesn't happen in practice because of vibration and changing of speed, but hey, I'm just pointing out the physics.

centrifugal force

[BobbyR]

If you get the clear tubes working the rule of thumb is: the fuel level should be no higher or lower than the lower edge of the float bowl lip. This will keep the bowl gasket from being immersed in gasoline. Of course on turns there will be brief contact. The tube should be held against the float bowls, I found I can influence the heigt of the fuel in the tube by moving the tube away from the bowl.   

Theoretically, since motorcycles lean in turns the fuel should always stay level in relation to the float bowls. Obviously this doesn't happen in practice because of vibration and changing of speed, but hey, I'm just pointing out the physics.

centrifugal force

Granted, It is also dependent upon the angle and speed of the turn. Pulling into your driveway it would like tilting a glass.

[tlbranth]

Here's the setup. Definitely some kind of setup problem. Thanks for the replies - I was pretty sure the level was top-of-the-bowl-ish. I've modified the floats to fix leaking problems caused by dimples in the tangs and had to make significant adjustments. Now I need to figure out why my setup isn't working. When I get this whole thing figured out, I'll publish my dimple fix.

[flybox1]

Terry,
The setup looks fine.
Enough fuel in your aux supply to fill all bowls?
Tap on your carbs as you turn on the gas to un-stick the floats.
Are your brass floats filling with fuel?

[tlbranth]

Floats are good. Plenty of fuel in supply. I'm thinking it's an air bubble in the supply line. I've always been baffled by that possibility but I know it happens. So I'll check that out. Thanks for the help.

[BobbyR]

Just out of curiosity and ignorance, why didn't you put the tube on the drain at the bottom?  I have a K8 so it may be different.

[flybox1]

Just out of curiosity and ignorance, why didn't you put the tube on the drain at the bottom?  I have a K8 so it may be different.

Only our PD carbs allow the bowl to 'drain' out the overflow.(top photo)

These older carbs drain screws let fuel flow out their seat.  They only 'overflow' out the overflow tube when the fuel level gets too high.

types...


vs

[tlbranth]

Well it's not an air bubble problem. Here's the full disclosure: All my float tangs were dimpled and I was having fuel leak problems. I came up with a fix for it that I hoped would be repeatable. I soldered a new piece of brass plate (.015") to the dimpled side of the float tangs. I don't think the weight of the addition is significant. It's probably about 4mm square and it's close to the float fulcrum. I knew that a fairly major adjustment was in order though and that's what I'm trying to do now. So I'm thinking of maybe scrapping the float-setting tool and just going for 3mm from top of bowl. What about that?
Where did you get those diagrams Fly? Does the 3mm apply to my K0?

[markreimer]

I have the non PD carbs and what I did was grab a spare float bowl and cut the overflow tube right down, so fuel would immediately flow out the overflow nipple regardless of the float setting. Then hooked up a clear tube and taped it to the side of the bowl. I still had obviously incorrect levels though. maybe an air bubble, I'm really not sure. It was odd.

[flybox1]

Well it's not an air bubble problem. Here's the full disclosure: All my float tangs were dimpled and I was having fuel leak problems. I came up with a fix for it that I hoped would be repeatable. I soldered a new piece of brass plate (.015") to the dimpled side of the float tangs. I don't think the weight of the addition is significant. It's probably about 4mm square and it's close to the float fulcrum. I knew that a fairly major adjustment was in order though and that's what I'm trying to do now. So I'm thinking of maybe scrapping the float-setting tool and just going for 3mm from top of bowl. What about that?
Where did you get those diagrams Fly? Does the 3mm apply to my K0?

^^  This...I am suspicious of.  The weight of the plate+solder might just be enough to keep your fuel levels low, no matter the measured/set height.
The float tang dimples can be polished out.  I successfully did this on my 550.

Do a search on GOOGLE images for carb clear tube test.  You'd be surprised at the number of forums where it is discussed and recommended.
I noticed this after my conversation with Hondaman.  Its just common practice for me now.  Set the float heights, clear tube test, and adjust as necessary.

[Bailgang]

I don't mean to get overly technical here but you said you were using kerosene on your bench setup, I don't know how relevant it is to your problem but kerosene generally has a higher specific gravity than gasoline does meaning the float will be more buoyant in the kerosene than it will be with gasoline so if you're setting your float level with kerosene then that level won't be exactly the same once gasoline is in the bowl. The specific gravity of pump gasoline varies depending on the grade or octane of the gas you intend on using, again I don't know how relevant that is to your situation but just to rule that out you may want to use what ever gasoline you usually run in your bike on your bench setup rather than kerosene and see if there is a difference.

[tlbranth]

I don't mean to get overly technical here but you said you were using kerosene on your bench setup, I don't know how relevant it is to your problem but kerosene generally has a higher specific gravity than gasoline does meaning the float will be more buoyant in the kerosene than it will be with gasoline so if you're setting your float level with kerosene then that level won't be exactly the same once gasoline is in the bowl. The specific gravity of pump gasoline varies depending on the grade or octane of the gas you intend on using, again I don't know how relevant that is to your situation but just to rule that out you may want to use what ever gasoline you usually run in your bike on your bench setup rather than kerosene and see if there is a difference.

That thought had occurred to me and I figure I should do a little side test on how well the float rides in each. I don't like using gasoline on account of the danger. Some always spills and some of my setup joints leak. I should just get one carb set using gasoline then fool around with the others to make them match using kerosene.

[BobbyR]

Well it's not an air bubble problem. Here's the full disclosure: All my float tangs were dimpled and I was having fuel leak problems. I came up with a fix for it that I hoped would be repeatable. I soldered a new piece of brass plate (.015") to the dimpled side of the float tangs. I don't think the weight of the addition is significant. It's probably about 4mm square and it's close to the float fulcrum. I knew that a fairly major adjustment was in order though and that's what I'm trying to do now. So I'm thinking of maybe scrapping the float-setting tool and just going for 3mm from top of bowl. What about that?
Where did you get those diagrams Fly? Does the 3mm apply to my K0?

^^  This...I am suspicious of.  The weight of the plate+solder might just be enough to keep your fuel levels low, no matter the measured/set height.
The float tang dimples can be polished out.  I successfully did this on my 550.

Do a search on GOOGLE images for carb clear tube test.  You'd be surprised at the number of forums where it is discussed and recommended.
I noticed this after my conversation with Hondaman.  Its just common practice for me now.  Set the float heights, clear tube test, and adjust as necessary.

As a practical matter, if this repair is suspect would it not be easier to just get a new set of floats and be done with it. If the cost is an issue I apologize. I would rather be riding than working on the bike. I was raised by a "jury rigging make do guy" so that is my inclination. I have come to realize sometimes it is simply not worth it.

[Duke McDukiedook]

If you get the clear tubes working the rule of thumb is: the fuel level should be no higher or lower than the lower edge of the float bowl lip. This will keep the bowl gasket from being immersed in gasoline. Of course on turns there will be brief contact. The tube should be held against the float bowls, I found I can influence the heigt of the fuel in the tube by moving the tube away from the bowl.   

Theoretically, since motorcycles lean in turns the fuel should always stay level in relation to the float bowls. Obviously this doesn't happen in practice because of vibration and changing of speed, but hey, I'm just pointing out the physics.

centrifugal force

Actually the force you speak of in a turn is centripetal force. And using any other liquid than the gasoline you intend to use when riding will slightly skew your results due to different specific gravity of the fluids in question as tl pointed out.

[jonda500]

Hey tlbranth, I really like your jury rig. I'm with you and think such a tiny piece of brass so close to the pivot would have a negligible effect on the weight of the floats and if you are setting the fuel levels with clear tube tests, I can't see why it wouldn't work. Thanks for sharing your idea. Let us know how it goes!
John

[tlbranth]

I liked DaveBarbier's idea of a clear plastic bowl and became frustrated with not trusting what I was seeing. So I went dumpster (recycle bin) diving and came up with a smallish plastic bottle. I cut a section from the bottle and after removing #1 bowl and spring clip, set the bottle bottom on a block under #1. It was an eye-opener. The level was at least 10mm different from what I saw with the clear tube. I adjusted the float 'til the level was 6mm below the outer part of the body flange at it's low point. Then I did the same with #4. This setup didn't work on the middle two carbs because the bottle was too big. But I revisited the recycle bin and came up with an empty bodywash container from Costco. It's a triangular shape and fits well on all the carbs. I adjusted the middle two carbs to the 6mm setting too.
This setup, I think, is better than the clear tube method because something happens to give false readings with the latter. My physics background tells me it should work but I think someone with an engineering background and knowledge of material properties would know that pure science don't allus work in the real world.
An advantage to the bottle method is that you don't have to keep removing the bowl to make an adjustment. The bad is: you'll have spilled fuel everywhere - hence the kerosene ploy.
My bike runs rich which is why I chose 6mm. From what Flybox1 said, it should be 3mm. But I'll give this a try and see how it goes.
I will post some pics on another thread of my dimple fix. I think it's a good, easily repeatable, fix. And trust me, those innocent looking little marks are deeper than they look and will hang up your float and make the carb overfill & leak.

[markreimer]

Heyyyy, now that is a clever idea! That would be SO much easier than pulling the bowl on and off over and over. I love it! After my failed clear-tube method (same issue as you had) I think i'll give this a try.