Topic: Setting the float level

[odiewan]

Ok, so on my CB750k3 I have totally rebuilt the carbs. I set the float level according to the manual (26mm from the body to the lowest point on the float), but when I park the bike it seeps gas out the overflow (slowly, but surely) if I don't turn off the stopcock valve.

Is this normal?

Regarding setting the float level, do you set the float level from the flat area the float gasket sits on or the lip surrounding it?

Seems to me that if I set it to the lip that would have a lower float level and thus a lower level of fuel in the bowl.

Or is my leaking gas more to do with the condition of my float valve seal?

[Elan]

Is it overflowing from all 4 carbs? That would tell you its more likely your float setting than the valve...

[climbingaz]

Just my guess....but if it's just one or two lines that are leaking, it's probably a float valve sticking or not fully seating vs. the float height.

[fasturd]

check the overflow tubes to make sure if just one or all carbs are leaking. If its just one you may have a bad seal if all are leaking you have 4 or another problem... And no matter where you set the float height if the tang to depress the float valve is not contacting the float it wont shut off the valve. Don't ask me how I got a measurement that didn't shut the valve off...

[odiewan]

Thanks for the response fellas. Don't really know if it's all of them or one. Sounds like I need to attach a container to each one and find out.

[Toxic]

I thought I was meticulous in my float setting but I'm glad I set it up this way.

I took me 3 attempts to get it right.   It's allot easier this way than pulling them off the bike each time.

[SOHC Digger]

Fuel leaking out the overflow is a fairly common problem in my experience.  The new float valves (I'm assuming they would have been replaced upon rebuild) need to seat themselves just like new piston rings need to be seated.  I suggest shutting the petcock off when the bike is not running.  When the bike is running and this occurs, shut off the petcock and let the engine suck the fuel down in the carbs.  When the bike starts to stumble, turn the petcock back on.  This may take several cycles of this process.  It sucks, but it's not uncommon.

[flybox1]

yes, its common, but easily fixed.
when you turn your fuel on, gently hit the bank of carbs (or the bowls of the leaking carbs) with a rubber mallet, or chunk of wood.
if this stops the leak, then you just free'd the stuck float.

if it does not work, then you have a poorly seated, or crud-blocked float valve.
remove and clean, and verify correct float height settings.

[Kong]

Get yourself a couple of feet of clear quarter inch aquarium tubing.  Cut off 4  lengths of it long enough that you can slip one end over the overflow tube and then wrap the tube into a 'U' shape with the open end sticking up about half the height of the carb.  Next open up the carb drains, with the petcock open.  What will happen is all 4 of the little tubes will fill up to exactly the same level as the fuel in the bowls.  So if your floats are set right and working right all 4 of them will be 26mm below the float chamber rim.  But if one or more of them is leaking you'll see a considerably higher level on that or those tubes.

[srook]

You might want to reclean the seat that the float needle contacts to ensure that there is an adequate seal.  I used a plastic zip-tie to clean the seats on mine.  Use the end that is v shaped and scrape the edges of the seat with it.  You won't damage the brass and the plastic zip-tie end will scrape anything off there that could hold the float needle from seating.  I would also re-check the float height.  You would be amazed to find out that the measurements are probably not where you set them the first time.  The bowls can push on the floats sometimes during assembly and change your original settings.
Scott

[odiewan]

Awesome advice guys. Thanks much. I like the little manometer setup, very clever.

[SOHC Digger]

Get yourself a couple of feet of clear quarter inch aquarium tubing.  Cut off 4  lengths of it long enough that you can slip one end over the overflow tube and then wrap the tube into a 'U' shape with the open end sticking up about half the height of the carb.  Next open up the carb drains, with the petcock open.  What will happen is all 4 of the little tubes will fill up to exactly the same level as the fuel in the bowls.  So if your floats are set right and working right all 4 of them will be 26mm below the float chamber rim.  But if one or more of them is leaking you'll see a considerably higher level on that or those tubes.

This is a good idea, Kong.  I will be using it in the future for sure.  Thanks!

[odiewan]

Ok, so one last thing. In my original post I asked about were exactly do you measure the float level.

Is it from the surface of the float bowl seal, the rim or the sealing surface on the carb body?

An idea I had if this is fairly common is doing something Suzuki did with their early SVs (carburated models): they had a vacuum operated stopcock. Haven't been able to find an inline version yet.

[Kong]

With the carb hanging up side down you measure from the base of the carb body (which should be horizontal) to the part of the float that is as far from the pin as possible and facing up - measured to the top.  It will make a lot of sense to you if you look at the special tool that is made for the process, and as luck would have it you can go to E-Bay and look at one that is for sale:

http://cgi.ebay.com/ebaymotors/Honda-CB750-Carb-Float-Level-Setting-Gauge-cafe-racer-/390277607832?pt=Motorcycles_Parts_Accessories&hash=item5ade5bb198#ht_1632wt_1167

You see the little tits that stick down in the picture?  Those are put in contact with the carb body on the underside of the float chamber and then the cutout has to match the float height.  Make sense?

[odiewan]

ya, that makes sense.

But you know what makes more sense? Spending $30 and getting the dang tool!

[Kong]

ya, that makes sense.

But you know what makes more sense? Spending $30 and getting the dang tool!

You know, some folks say that Baboons are the smartest things ever to climb down out of the trees, but if you ask me humans don't do so bad sometimes either.

[paulages]

Get yourself a couple of feet of clear quarter inch aquarium tubing.  Cut off 4  lengths of it long enough that you can slip one end over the overflow tube and then wrap the tube into a 'U' shape with the open end sticking up about half the height of the carb.  Next open up the carb drains, with the petcock open.  What will happen is all 4 of the little tubes will fill up to exactly the same level as the fuel in the bowls.  So if your floats are set right and working right all 4 of them will be 26mm below the float chamber rim.  But if one or more of them is leaking you'll see a considerably higher level on that or those tubes.

That won't work as you described it, unless the fuel level is above the level of the standpipe inside. The sight tube needs to come from the drain plug. I have test bowls on which i've installed fuel nipples permanently into the drain holes in order to test the fuel level this way.

[Spanner 1]

Nonsense... $30 for a tool to set your float levels   .. Crazy. All you need is an old credit card with a cut-out that exactly measures 26mm ( for O.P.'s K3 carbs ). And your setting of 26mm will be wrong unless the carb bodies are vertical, never upside-down as the weight of the float will press on the float valve spring.
Do it right the first time  ... Again, carbs sideways, bowl to body surface vertical, float pin on top, float tabs barely touching the valve...first press on the valve and release ( to make sure it is all the way in it's seat ), now measure....  

[Nortstudio]

This might seem crazy (or closer to those baboons Kong mentioned) but when I first cleaned my carbs, they leaked like crazy. Forum member here (Tango) suggested I rock the bike back and forth, about the amount it would lower onto the kick stand.

As nuts as it sounds, it stopped leaking after about 5 swings to each side. Make sure you have a pal to help if you're worried about dropping her to the far side. But for me, 30 seconds and it worked like a charm.

My guess is the sloshing perhaps loosened the stuck float valve.

[Gaither]

FWIW

When we "did" my carbs, we found a tiny (difficult to see) crack in one of the overflow tubes - evidently a fairly common problem - and definitely a permanent leak - regardless of float setting.

Easily repaired with shrink tubing.

Just a thought -

[CrankyOldGuy]

Just purchased the float level setting tool mentioned in Kong's e-mail above.  There were none left on the e-bay site when I went there, but I was able to purchase one directly from Lowbrow Customs (www.lowbrowcustoms.com) at $29.95 plus S&H which to me in Atlantic Canada was $2.01.

Thank goodness for the parity of the US and Canadian dollars; its much cheaper to buy parts now then when the Canadian dollar was worth 65 cents US. 

Harry O.

[scottly]

Get yourself a couple of feet of clear quarter inch aquarium tubing.  Cut off 4  lengths of it long enough that you can slip one end over the overflow tube and then wrap the tube into a 'U' shape with the open end sticking up about half the height of the carb.  Next open up the carb drains, with the petcock open.  What will happen is all 4 of the little tubes will fill up to exactly the same level as the fuel in the bowls.  So if your floats are set right and working right all 4 of them will be 26mm below the float chamber rim.  But if one or more of them is leaking you'll see a considerably higher level on that or those tubes.

That won't work as you described it, unless the fuel level is above the level of the standpipe inside. The sight tube needs to come from the drain plug. I have test bowls on which i've installed fuel nipples permanently into the drain holes in order to test the fuel level this way.

It will work fine this way on 750 carbs, which have drain screws instead of drain plugs. Also, the fuel level in the tubes should be about 2-3 mm below the rim, not 26mm, regardless of the carbs.
The clear tube method will show the actual level in the bowls; while the mechanical measurement might check ok, there may be other things, such as weak float needle plunger springs or leaking valves, that result in high fuel levels in the bowls.

[jleavesl]

I have a 1973 Honda cb500, but I believe that the carbs are of a similar design.  I have built two sets of carbs and bought a third.  If the tank is dirty, some of that crap will get stuck in the float valve.  Pull the o-ring off, dip it, blow it out with compressed air... And it should solve your problem.  Also, pull off the drain tubes so you know which carb is pissing.

[paulages]

Get yourself a couple of feet of clear quarter inch aquarium tubing.  Cut off 4  lengths of it long enough that you can slip one end over the overflow tube and then wrap the tube into a 'U' shape with the open end sticking up about half the height of the carb.  Next open up the carb drains, with the petcock open.  What will happen is all 4 of the little tubes will fill up to exactly the same level as the fuel in the bowls.  So if your floats are set right and working right all 4 of them will be 26mm below the float chamber rim.  But if one or more of them is leaking you'll see a considerably higher level on that or those tubes.

That won't work as you described it, unless the fuel level is above the level of the standpipe inside. The sight tube needs to come from the drain plug. I have test bowls on which i've installed fuel nipples permanently into the drain holes in order to test the fuel level this way.

It will work fine this way on 750 carbs, which have drain screws instead of drain plugs. Also, the fuel level in the tubes should be about 2-3 mm below the rim, not 26mm, regardless of the carbs.
The clear tube method will show the actual level in the bowls; while the mechanical measurement might check ok, there may be other things, such as weak float needle plunger springs or leaking valves, that result in high fuel levels in the bowls.

On the later PD carbs, yes. Not so on the early carbs.

[Kong]

Sorry for misleading those folks who have carbs the tube thing won't work on.  It works on the couple of sets I have here but it wasn't something I thought up or have even known about for long.  I saw it in one of the build threads when I first found this site and spent about a week just reading the archives before posting.

There is just this one thing I wanted to mention, and this is definitely about 550 carbs and definitely only about the later (77 and 78) versions of them.  When setting the float height you are shooting for (different sources show different float heights for these carbs) something in the 14~15mm level it just so happens that is the same height as the cast boss the idle adjustment screw resides in, which is right next to the float.  So you don't really even need a gauge, just set the float height even with the boss height.

As for setting the heights with the carbs vertical, that agrees with the Honda Service Manual's pictures (though not mentioned in the text).  It came as quite a surprise to me, apparently I've been doing it wrong for decades, albeit with consistent success.  I don't think it will make any difference which way the carb is oriented though.  It seems to me that if the little spring-loaded pin at the end of the float-valve needle is compressed by the minuscule weight of the float it must have lost its rebound ability and the needle probably should be replaced.  I know mine don't compress - its something I check before I do the measurements actually, along with shaking the whole works to make sure that the floats are swinging freely.  At any rate Spanner-1 is right.  According to the Manual the floats should be set with the float chamber positioned near vertical, at just enough of an angle to make the floats gravitate toward their normally 'up' direction, and then make the measurement such minimal contact and pressure is exerted on the valve.

As for measuring it, while on my 550 carbs I just set them to the boss height, on any other carbs I just extend the tail-stock of my trusty veneer-calipers to the required setting, lock it, and then use it as my gauge.