Determining which carb is leaking

[scott]

I'm trying to determine which of my carbs is overflowing so I have pulled the carbs. I put them in a container and connected a remote fuel source. However, nothing seems to be leaking. I tried tilting them from more or less level to slightly askew on both sides. I expected to see fuel dripping from where the airbox connects to the carbs. Is there something I'm missing?

In case it's relevant, here's the background:

Part 1: Upon receiving the bike, I believed I was getting fuel into the oil. I replaced the petcock with a new OEM petcock.
Part 2: I still seemed to be getting fuel in the oil so I moved forward with the standard maintenance tasks:

• completely disassembled and dipped / cleaned carbs according to guide
• replaced the carb's o-rings, gaskets, pilot jet plugs and set float heights
• replaced intake boots and o-rings; sealed airbox cover; added carb vent hoses (originally, nothing was connected to these nipples)
• did a valve adjustment - all now have between 0.08mm - 0.10mm clearance
• bench synched carbs
• mounted the airbox to the frame (airbox was originally just hanging there so I ordered a bolt & rubber spacer)
• highest-idle mixture screw setting (not entirely confident about this but they're around 3 turns out)
• vaccuum synched carbs using a homemade manometer (not entirely confident about this either)

After the carbs were back on the bike, I have been riding the bike during/between my various carb tuning steps. The oil level does not seem to be increasing anymore. However, during the vacuum synch and after all subsequent rides, I am noticing dripping from what I believe is the airbox "drain hose". I'm reasonably sure it's fuel (what else could it be). I didn't notice the dripping before the vacuum synch but I wasn't really looking for it and it seems unlikely that could cause it.

My take from this is that I still have an overflowing carb(s). I found it odd that now it's going to the airbox side and not the oil/crankcase. It's possible this is because I mounted the airbox to the frame instead of just letting it hang there but I would expect that to have the opposite effect (tilting the carbs more towards the engine-side).

Anyway, I ordered 1 OEM needle valve and seat set, hoping that I only have 1 problem carb. When doing the carb cleaning above, I noticed that carb #4's needle valve spring seemed weaker than the others so that seems like the most likely culprit. I wanted to confirm that this was the problem carb definitively so I am attempting the test above.

 

[tom203]

How is the condition of your gas tank? Assuming you have float heights close, yeah, it seems that at least one needle seat is not holding and letting fuel flow into airbox - but it could be crap causing it not to close. If you still have OEM vacuum petcock, it shouldn't be much when bike is off.

 

[dueller]

Double check petcock

Double check petcock

I know it's new, but just to make sure, hook up some hoses and make sure not still leaking? I had the same problem with leaking carbs, but mine was due to mistaking the vent port on the carb bodies for the vacuum port to the petcock. So I was blocking off the vent instead of the vacuum and creating a positive pressure inside the 1 & 2 carb bowls and the needle valves weren't able to seat properly. I had fuel leaking out of the air passage across from the air jet port though. Are you having trouble with getting steady idle? I couldn't get mine down under 4K! Catch the fluid leaking out in a clear bottle. Does it smell like gas? Look like gas?

 

[scott]

How is the condition of your gas tank?

From what I can see, it doesn't look too bad:

Assuming you have float heights close, yeah, it seems that at least one needle seat is not holding and letting fuel flow into airbox - but it could be crap causing it not to close. If you still have OEM vacuum petcock, it shouldn't be much when bike is off.

The dripping from the airbox vent hose occurs for a while after the bike is off and then stops so I don't think it's the petcock.

If there was rust or something from the gas tank clogging something up OR if there were a problem needle valve / seat, wouldn't that still be the case if I hooked up a remote fuel source with the carbs off the bike (since the clogging debris would still be there)?

 

[scott]

I know it's new, but just to make sure, hook up some hoses and make sure not still leaking? I had the same problem with leaking carbs, but mine was due to mistaking the vent port on the carb bodies for the vacuum port to the petcock. So I was blocking off the vent instead of the vacuum and creating a positive pressure inside the 1 & 2 carb bowls and the needle valves weren't able to seat properly. I had fuel leaking out of the air passage across from the air jet port though.

The tank is off the bike now - I haven't noticed any leaking. Since the drip stops eventually when the bike is off, I was assuming the petcock could be eliminated. Plus even if the petcock was bad, wouldn't the needle valves be expected to stop the fuel anyway? I'll double check the hoses (they're all still on), but I'm pretty sure they're correct.

Are you having trouble with getting steady idle? I couldn't get mine down under 4K!

I've only taken a ride or two after the vacuum synch but the idle seemed fairly steady. Before that, sometimes it would idle as high as 1.5K but never anything like 4K. A few times during very hot days, the idle would drop very low and it would die. That hasn't happened since the vacuum synch (hasn't been very hot though).

Catch the fluid leaking out in a clear bottle. Does it smell like gas? Look like gas?

I caught some in a plastic dixie cup. The color was a little yellowish. It smells pretty much like gas. It also "melted" the cup which happened before when I had gas in one of those cups.

 

[scott]

I had the same problem with leaking carbs, but mine was due to mistaking the vent port on the carb bodies for the vacuum port to the petcock. So I was blocking off the vent instead of the vacuum and creating a positive pressure inside the 1 & 2 carb bowls and the needle valves weren't able to seat properly. I had fuel leaking out of the air passage across from the air jet port though.

Ok I checked my hoses - they look right to me:

The above pic also shows how I'm trying to reproduce the leak off the bike (there is a remote fuel source hooked to the fuel hose). Could the reason it's not leaking off the bike be due to the lack of vibration or something like that?

 

[scott]

Well, I guess I've had "success". In order to simulate the on-bike environment more closely, I tried jostling/shaking/tilting the carbs. I'm not sure if I went overboard (beyond what would happen on the bike) but I was able to get some fuel to leak. Carb #3 seems to be leaking most. I THOUGHT some may have leaked from Carb #1 but I couldn't reproduce it.

Interestingly Carb #4 was the one with the needle valve spring that seemed a bit weak. I was hoping that would be the offending carb because I have a feeling that needle valve will need replacing sooner or later. Oh well.

In any event, I'll start with Carb #3. I'll re-check it's float height and if it seems fine, I'll go ahead and replace it's needle valve and seat.

I also noticed something odd with one of the sliders but I'll post that in a new thread because to my knowledge it does not seem related to my leak/drip.

 

[tom203]

Well, I guess I've had "success". In order to simulate the on-bike environment more closely, I tried jostling/shaking/tilting the carbs. I'm not sure if I went overboard (beyond what would happen on the bike) but I was able to get some fuel to leak. Carb #3 seems to be leaking most. I THOUGHT some may have leaked from Carb #1 but I couldn't reproduce it.

Interestingly Carb #4 was the one with the needle valve spring that seemed a bit weak. I was hoping that would be the offending carb because I have a feeling that needle valve will need replacing sooner or later. Oh well.

In any event, I'll start with Carb #3. I'll re-check it's float height and if it seems fine, I'll go ahead and replace it's needle valve and seat.

I also noticed something odd with one of the sliders but I'll post that in a new thread because to my knowledge it does not seem related to my leak/drip.

Your tank looks ok. Your off the bike setup is bound to leak if you shake the carbs hard enough- when bike is bouncing down road, fuel is being consumed so it's not as likely to overflow. Your hoses are correct. Is this petcock the kind with "on", "res' ,and "prime" ?

 

[scott]

Your tank looks ok.

Thanks for the confirmation. I was hoping that little bit of rust was nothing to worry about.

Your off the bike setup is bound to leak if you shake the carbs hard enough

Yeah - I was thinking that. With my "test", Carb #3 seemed most likely to drip/leak followed by Carb #1. The others didn't really leak at all unless I tilted the rack way over.

You're probably right that I didn't get any useful information out of that "test" though. I guess it tells me my fuel level is highest on Carb #3 so I'm going to check the float height next. I still haven't decided which carb should get the new needle valve / seat. I suppose I could just save it, but I have it so I figure I might as well stick it in one of them. Since I haven't really identified a cause, I get the feeling the bike is going to still drip when I get the carbs back on. The bike was running with the drip so maybe it's not a big deal.

Is this petcock the kind with "on", "res' ,and "prime" ?

It has On and Res with a prime screw. This pic shows it in the On position.

 

[terrylee]

Make sure all your float levels are right on spec. that can make a big difference. If ok you're right could be float needle valves are worn. Also is it possible stuff coming out of air box is extra oil from your air filter (if over oiled)or perhaps due to oil vapors from the breather on top of valve cover which has a hose going into airbox? terrylee

 

[scott]

I set Carb #3's float level to be 23.40 (it was around 22.90) so I put it at the upper end of the spec in order to reduce the fuel level. When tilting the carbs over, that carb poured fuel first so I'm assuming it had the highest fuel level. I also replaced the needle valve / seat in Carb #4 (the carb with the weak needle valve spring).

I put the carbs back on the bike and took it for a ride. It's still doing the same thing - dripping fuel from the airbox drain hose. I really don't understand why it didn't leak when hooked up to a fuel source off the bike but seems to drip consistently on the bike (at least after a ride).

Make sure all your float levels are right on spec. that can make a big difference.

Is there a connector piece similar to what is used to hook a tube to the intake boot vacuum port that can be hooked to the float bowl drain? I've read suggestions to check the float level with a clear tube.

If ok you're right could be float needle valves are worn.

I replaced the most likely culprit. I suppose I could replace the other 3 but it's expensive so I'd like to avoid that if possible. I can't imagine they're all bad - my off-bike test was supposed to tell me which to replace.

Also is it possible stuff coming out of air box is extra oil from your air filter (if over oiled)

I suppose it's possible but I recently cleaned the filter element and only gave 2 VERY brief spritzes on each side using the K&N aerosol air filter oil. I would think it's more likely to be under-oiled. I really doubt I over-oiled so much to cause dripping after every ride too.

or perhaps due to oil vapors from the breather on top of valve cover which has a hose going into airbox?

Well I can definitively say it's not this one - one possibility off the table! I had forgotten to reconnect this hose to the valve cover when I took my first ride after putting the carbs back on the bike (and it still dripped).

I collected the fluid dripping from the airbox after a ride.

I'd say it's fuel and it doesn't seem like too much (there may be even some water mixed in there from when I rinsed the bottle prior to collecting the drip). It's a 12oz Snapple bottle.

 

[tom203]

Very strange for fuel to find it's way to airbox during a ride! Would it be possible to put strip of clean cardboard in airbox aligned under carb intakes and go for ride and maybe see which carb seems to be at fault?

 

[Souske]

I had good luck just running my bike with the carbs open

 

[scott]

Very strange for fuel to find it's way to airbox during a ride! Would it be possible to put strip of clean cardboard in airbox aligned under carb intakes and go for ride and maybe see which carb seems to be at fault?

This is an interesting idea. So I would take off the air filter cover, remove the air filter cage, stick a rectangular piece of cardboard through the hole into the carb section of the airbox. Put the airbox back together and then go for a quick ride (so the cardboard doesn't get saturated) and see if there's spots under a certain carb?

 

[scott]

I had good luck just running my bike with the carbs open

You mean without the airbox / using pods? I'd love to, not for any performance reasons but because I can't stand removing/re-fitting the carbs (allegedly it's a tighter fit on the 550 model). However, I've read on here that it makes it much harder to get the bike running right. Since I don't really know what I'm doing, I'd like as few variables as possible.

 

[tom203]

This is an interesting idea. So I would take off the air filter cover, remove the air filter cage, stick a rectangular piece of cardboard through the hole into the carb section of the airbox. Put the airbox back together and then go for a quick ride (so the cardboard doesn't get saturated) and see if there's spots under a certain carb?

That was my plan!

 

[Souske]

You mean without the airbox / using pods? I'd love to, not for any performance reasons but because I can't stand removing/re-fitting the carbs (allegedly it's a tighter fit on the 550 model). However, I've read on here that it makes it much harder to get the bike running right. Since I don't really know what I'm doing, I'd like as few variables as possible.

Makes sense, I am using pods because that is what my bike came with. It used to pee so much gas it would drip from the pods while running. Changed the inlet needles/seats/orings on offending carbs and no more leaking.

Good luck on the cardboard method, sounds like a good idea!

 

[scott]

Well, I put a strip of cardboard in the airbox. I actually had to cut it into 2 pieces to get it to fit - that air filter hole isn't as big as I thought, I couldn't' fit my hand in there too easily. It didn't look like it moved though during the ride. I took a short ride (idled on choke for maybe 3 mins, rode it for maybe 5 mins) and here's the results.

The top of the cardboard (facing the carbs/holes):

The bottom of the cardboard (laying on the airbox "floor"):

Perhaps the bottom is wet from where it collected on the sides? I was thinking the sides of the airbox were higher than the middle but maybe not.

I did try to dry out the airbox before putting in the cardboard strip. It seemed like it was a little oily but not wet. I didn't knock myself out drying it though so it's possible that was already wet but I don't think so. Also, it had been 24 hrs since the bike was run previously if that means anything.

Based on the top of the strip, it seems like it's coming out of ALL the carbs to varying degrees! Carb #1 and #2 seem worse. Would the mixture and/or synch have anything to do with this? Would a rich mixture cause this or idling too long on choke

 

[tom203]

Well, I put a strip of cardboard in the airbox. I actually had to cut it into 2 pieces to get it to fit - that air filter hole isn't as big as I thought, I couldn't' fit my hand in there too easily. It didn't look like it moved though during the ride. I took a short ride (idled on choke for maybe 3 mins, rode it for maybe 5 mins) and here's the results.

The top of the cardboard (facing the carbs/holes):

The bottom of the cardboard (laying on the airbox "floor"):

Perhaps the bottom is wet from where it collected on the sides? I was thinking the sides of the airbox were higher than the middle but maybe not.

I did try to dry out the airbox before putting in the cardboard strip. It seemed like it was a little oily but not wet. I didn't knock myself out drying it though so it's possible that was already wet but I don't think so. Also, it had been 24 hrs since the bike was run previously if that means anything.

Based on the top of the strip, it seems like it's coming out of ALL the carbs to varying degrees! Carb #1 and #2 seem worse. Would the mixture and/or synch have anything to do with this? Would a rich mixture cause this or idling too long on choke

What, nobody is leaping to a conclusion? Short ride like that, it seems they are all spitting back into airbox. I doubt it's the choke, cuz in normal ride, it's off and any excess fuel would be sucked in as the bike ran and you wouldn't find it. It has to be spraying out carb throats or thru air jet orifice - but that takes back pressure of some sort.

 

[scott]

What, nobody is leaping to a conclusion?

Yeah - I figured there'd be some interpretations of my little Rorschach test.

Short ride like that, it seems they are all spitting back into airbox.

So basically, even a little spitting back into the airbox is indicative of a problem?

I doubt it's the choke, cuz in normal ride, it's off and any excess fuel would be sucked in as the bike ran and you wouldn't find it. It has to be spraying out carb throats or thru air jet orifice - but that takes back pressure of some sort.

That sounds like something would impact all the carbs which seems to match the symptoms. What can create back pressure?