Topic: Cb400f float demons

[kyre]

Hey guys, I've got spitting coming out my overflow tubes, only after a ride where I go over some larger bumps. If it's a smooth ride they don't leak. Just sitting there with fuel on, no leak. 

Cb400f bored to 466
Stage 2 porting by mrieck
Yoshima exhaust
95 mains
38 pilot
Air screws 1.5 turns out
Everything was ultrasonically cleaned
Bored stock carbs from Rick Denoon
Velocity stacks with small filters
New OEM float valves and seats (they definitely are sealing)
Tank is spotless
New fuel line
All vents are clear
New petcock with in tank screen
Inline fuel filter (no metal bits anywhere)

I just adjusted my floats to 25mm (stock is 21) but I wanted to see if I could eliminate this.. I did the clear tube method too after and all were 4mm below the bowl seam.

The bike runs amazing, it's just this one little annoying thing that is still baffling me after a year of messing. Dribbles of fuel on my exhaust sucks and I feel like I've done everything besides buying new floats.

Could the floats themselves be toast? Would going over bumps slosh the fuel and intermittently bounce the float and open the valve enough to have them dribble over? I feel like if that were the case all bikes would leak.

I'm really good at taking my carbs on/off now but that nothing to be proud of right now.. Anybody shed some light? If you need more info or details let me know.

[MoMo]

Did you check the stand pipes for hairline cracks?

[kyre]

Oh yeah forgot to mention that... Yes! None whatsoever and I checked a million times.  If there were cracks it'd always leak. I can leave the fuel on all day long while just sitting there and not a dribble will come out.  Only happens when I ride. 

[harisuluv]

Well your float height is way off.  One thing that results from this is the angle of the valve coming out of the seat can be odd.  This can sometimes cause it to "stick."  That would make sense since what you are experiencing is during riding, or in other words, when the valves are going up and down, as opposed to them not moving at all when it's just sitting there.

Is it coming from all four overflows?  If  you are looking at the bundle of four overflow tubes and see a leak, you need to trace it back specifically to the offending carb.

Since you have new Honda OEM seats, that's probably not your problem.  I would inspect your float tangs for a small dimple where the valve spring contacts, this can also catch.  Carefully file it down a bit.

You should return your floats to the stock height.  A lot of people set them to 23mm ish but that is because aftermarket float valves have a larger spring/plunger.  You don't have that issue, so you can use the stock height. 

[kyre]

I had it set to stock height (21mm) and it was still happening. The only reason I changed the height was to try and stop this dribbling by lowering the fuel level (didn't work obviously).  It's coming out of all four carbs btw. I also already filed down the old dimples and polished the tangs last year when this started happening. I might just bite the bullet and buy new floats but I'll be pissed if it still dribbles. They aren't cheap!

[bjbuchanan]

I think it is the float height. Some tweaking works but that is such a big difference from stock. Bring the height closer to stock by atleast a mm and see if that stops the dribbling, I bet it does.

The jarring from road surfaces is probably letting it overflow just a tiny bit and because you are set so high it doesn't take much to cause it to happen

EDIT

Do not buy new floats, that is in no way a solution to your problem. If you have a float with a hole in it it will be full of gas and will be really obviously bad. Otherwise don't bother with the floats, you have no reason so far to spend the money. Unless you like supporting our vendors

Floats could be binding like Harisluv says, You are dealing with an arc and a fixed object. You get the arc way out there and it could bind causing the float to hang up (in theory)

My bet is still on my pre-edit, fix your float height

[harisuluv]

Floats don't really "go bad."  They are just gas resistant foam/plastic they don't get "punctured" or go bad.  It's not the buoyancy of your floats.  If you "bite the bullet" and buy new floats, you will most likely be wasting your money. 

You have a pretty simple problem.  How do you know it's coming out of all four, if it were coming out of all of them there would be some gas on the end of the bundle, getting the tips wet, how are you determining it's from all four?

Your floats are probably tweaked far from original angles by now.  In other words the brass part of the float is a plane, and the line on the side of the float is another plane.  Those two planes should be parallel.

And how do you know it's dribbling while you ride?  Are they not set up to vent to where they basically just dribble onto the ground?  You mentioned some spots on your exhaust, but if that's your bike in your profile pic you have a 4-1?  In other words, they are ALL dribbling onto one side of your bike (the one with exhaust).
What do these dribbles on your exhaust look like?  Are you sure it's gas?

Also, many times people see gas at the ends of the overflow tubes (the rubber ones) and decide the gas is leaking out the overflow.  When in fact, they could just be leaking from somewhere else, fuel connectors between each carb, whatever.  Gravity then transports it to the drain tubes.

PS.  A picture is worth a thousand words.

[s7paul]

Floats don't really "go bad."  They are just gas resistant foam/plastic they don't get "punctured" or go bad.

Sorry for slight thread hijack, but are you saying the floats aren't hollow, i.e. they can't fill with fuel?

If so, I never knew that, but it would certainly stop me being concerned over the condition of the floats, and whether there could be any leakage into the float in the area where the brass bracket is moulded into it.

[harisuluv]

You referenced the material "molded around the float" so it sounds like you're also talking about the black synthetic float.  Obviously the earlier brass carbs can be punctured.

The black ones don't float cause they are hollow, the material itself is buoyant.  Throw a piece of styrofoam on water, it floats.  Not because it has a hollowed out center, but because the material is buoyant.

You could probably drill right through one and never notice it (depending on the size of your drill bit).  The only thing that would matter would be the amount of volume removed from the float.

[kyre]

How I know it's coming out all four tubes is I decided to lightly roll a bit of paper towel and put a dry piece in each tube. Then went for a ride and they were all soaked with gas when I came back. 


Everyone is saying bring floats back to stock height but the thing is this all happened when they were at stock height.  I only changed to try and solve the issue. I'm going to re-set them back but I guarantee it'll still happen.  I'll quadruple check the tang when I set back to stock height today.  Oh and I won't buy new floats.  That was desperation talking. 

[kyre]

Also I do have a 4-1 but the bundle of tubes all sit above the exhaust since this exhaust sits directly under the bike and then angles up a bit after where the center stand would be.  (Have to take it off for this exhaust)

[harisuluv]

Yes it is has been advised that you bring floats back to stock height.  No one has mentioned that this is going to "fix" your problem.  You already said that you had this problem with the stock float height.  So it's not the float height.  So, might as well go back to the stock float height is the reasoning.  No one expects that to fix your problem.  But if you are trying to diagnose something, it helps to have as many things that are stock or can be eliminated.

The paper towel experiment was decent, however it was flawed.  A paper towel can "wick" quite easily.  Meaning anything soaked at the bottom can travel all the way up.  Why not just separate them, clip them with something very firm each at the end then go for a ride, come back and unclip at the bottom and see which one leaks out gas?  Of course they will have to be COMPLETELY DRY before, and blown through with compressed air.

Also as I said, you did not eliminate other leaks from the same area or above that simply dripped down the drain tubes all the way to the bottom.

You need to reassess what you think you "KNOW" about the situation.  You are making assumptions and then testing with a flawed methodology. 

A pictures is worth a thousand words.  I can tell you how badly your floats are tweaked from a clear, side view of the float.  Again..  It's not necessarily the tang but the tang bent relative to the rest of the brass.  In other words, I can grab the pin pivot with needle nose pliers and twist up or down and adjust the tang without even touching it.  This is "adjusting" the tang but by just altering other geometries.  Things like this when tweaked incorrectly will cause the float valve to get caught because the angle of depression from the tang is so awkward.  Hold up your body upright, and you can see how far the valve comes out of the seat, and at what angle the tang is touching it.  I suspect this is your real problem.

[grcamna2]

Could the foam/plastic these floats are made of be 'fuel heavy' by possibly absorbing fuel/ethanol into their pores ?

[harisuluv]

nah.

[grcamna2]

Yes it is has been advised that you bring floats back to stock height.  No one has mentioned that this is going to "fix" your problem.  You already said that you had this problem with the stock float height.  So it's not the float height.  So, might as well go back to the stock float height is the reasoning.  No one expects that to fix your problem.  But if you are trying to diagnose something, it helps to have as many things that are stock or can be eliminated.

The paper towel experiment was decent, however it was flawed.  A paper towel can "wick" quite easily.  Meaning anything soaked at the bottom can travel all the way up.  Why not just separate them, clip them with something very firm each at the end then go for a ride, come back and unclip at the bottom and see which one leaks out gas?  Of course they will have to be COMPLETELY DRY before, and blown through with compressed air.

Also as I said, you did not eliminate other leaks from the same area or above that simply dripped down the drain tubes all the way to the bottom.

You need to reassess what you think you "KNOW" about the situation.  You are making assumptions and then testing with a flawed methodology. 

A pictures is worth a thousand words.  I can tell you how badly your floats are tweaked from a clear, side view of the float.  Again..  It's not necessarily the tang but the tang bent relative to the rest of the brass.  In other words, I can grab the pin pivot with needle nose pliers and twist up or down and adjust the tang without even touching it.  This is "adjusting" the tang but by just altering other geometries.  Things like this when tweaked incorrectly will cause the float valve to get caught because the angle of depression from the tang is so awkward.  Hold up your body upright, and you can see how far the valve comes out of the seat, and at what angle the tang is touching it.  I suspect this is your real problem.

I know the angle and configuration of the float 'tang' relative to the float/needle needs to be the same as stock after filing & polishing them,ask me how I know  

[harisuluv]

Yup.  It's usually an issue when you add aftermarket float valves/seat into the equation as they have different dimensions.

This is why people usually have higher than stock float height settings for the 350f/400f in particular.  Also, these floats lack a "stop" for the float, meaning that you can't adjust a tang to keep the valve from falling out excessively to the point where it might "catch." 

Because of that, it's extra important to have things adjusted properly.  The tang like I said could be adjusted, but people also tweak the float parts (black) just up and down, you can just bend them, without ever touching the tang.  Meanwhile the tang isn't correct spec for the valve to not almost fall out on its own.

[grcamna2]

harisuluv,
I've given up using K&L Supply float needles because the spring pressure was too tight in them on all the bikes I worked on in the past which somehow changed where the float would come to rest under pressure;OE float needles are the most 'carb. friendly' parts you can have. 

[harisuluv]

@grcanmna2 Yes, you can try and compensate with another 1-2mm float height, but it takes some experimenting.  I personally haven't had too much issue with aftermarket float valves when used.

Unfortunately, there is no real "satisfactory" replacement for many of the parts.  Genuine Kei-Hin parts have no substitute, agreed.

[kyre]

So the fuel definitely is not
Coming from a different source and runnings down the tubes.  On the very tips of the overflow tubes are a bit damp. Nothing coming from above. 

Attached are my floats from the side 1-4.

This currently at the 25mm. Changing back to stock height now. 

 

[kyre]

@harisuluv I definitely think you're right about the float valve angle.  Moving the float up and down I'm noticing the tang is tweaking the float valve at an angle. I really think this is what's causing fuel to slip by and thus filling the bowl too much.  Hopefully.  I'm going to make everything as parallel as possible and make sure that valve doesn't get pushing to the side when activated. 

[harisuluv]

That actually doesn't look too bad.  Pretty parallel.

If they were installed as shown there, they would be upside down, is that how they came off? 

[kyre]

Also here's a comparison to my old float valve on the left that never leaked and the new OEM float valve on the right.



Old never leaked. Not even sure why I thought I needed to replace. Probably because I was doing a lot of other work and thought new is better.  Anyways, are my old valves OEM? They have the rubber tip and my new ones don't.  The old one also fit in the seat a bit more snug.  New ones jiggle around a little side to side.  Also the new valves tip is a bit longer. 

I might put my old seats and valves in for a test. 

[kyre]

@harisuluv no the flat part is at the bottom when the carb is right side up.  I'm just used to seeing the floats upside down when off the bike

[harisuluv]

Ok, now we're getting somewhere.  The old valve is not correct!  That is for PD carbs 77-78 and later models!

The way you are talking it sounds like you are using the "new" valve in the old seat?  Otherwise why are you comparing how they "fit" cause they would each have their own corresponding seat.

Second, that does not look like an OEM valve, they usually don't have as long a plunger.  Exactly what do you mean by OEM?  And where did you get that new "oem valve" and did it come with a seat?  What was the labeling on the package and how much (about) did it cost?

[grcamna2]

Ok, now we're getting somewhere.  The old valve is not correct!  That is for PD carbs 77-78 and later models!

The way you are talking it sounds like you are using the "new" valve in the old seat?  Otherwise why are you comparing how they "fit" cause they would each have their own corresponding seat.

Second, that does not look like an OEM valve, they usually don't have as long a plunger.  Exactly what do you mean by OEM?  And where did you get that new "oem valve" and did it come with a seat?  What was the labeling on the package and how much (about) did it cost?

Harisuluv,
I think you have a lot of Heart to tackle 'this' problem here over the web ! 

[kyre]

Yes harisuluv I want to definitely thank you for helping me with this! I feeling like We're slowly getting somewhere.

First, new valve with new seat only. I'm comparing because I'm trying everything. What I meant was I put the old valve in the new seat just to see the fitment.  The new valve has some wiggle room where the old valve doesn't so much.

Ok so my old valves are incorrect. They never leaked in the 8 years they were on my bike before I tore into everything so I'm going to try to put those back in with their corresponding old seat and see what happens.  May as well since I've taken these off way too many times to count to try to fix the "new" valves. 

By OEM I mean I bought them from service honda and they had honda labeling. Seats and valves bought new at the same time.  Also they were really expensive. I believe around $30  each!! Ugh.


Guess I'll see what happens. I just put the old valves and seats back in and readjusted the float height to 21mm. When  the tang just touches the needle everything is very parallel.

[harisuluv]

Keep in mind those two planes being parallel is just a guide that I use to tell me if they have been tweaked in relation to each other, it tells you nothing about the tang being tweaked in relation to the rest of the brass.

Sounds like you have real honda OEM vales and seats.  I would use them cause they are quality.  The problem is probably still your floats hanging too much. 

[chewbacca5000]

 Can you take pics of the underside of the float tang.  Sometimes they get a small dimple that causes them to hang up.  I don't always remember to check, but if it has dimples smoothing them out with some 400 grit really helps out.

[harisuluv]

Oh and by the way the old "seats" for the rubber tipped valves aren't actually their seats.  The seats that those rubber tipped valves are paired with are a non removable pressed in brass seat for a totally different model bike and style carb.  So...  just sayin'.