Both carbs leak Fuel - Floats dont float - Vapour lock!

[weaselnoze]

Take them Out and Shake them if you feel and Hear Gas Sloshing Around toss them and Buy new Floats.I've Always had a bad Feeling about Plastic Floats and Vibration after they Turn Dark and Harden.With Brass Floats they were easily Fixable.With Plastic ones you may be able to fix them Temorarily with Epoxy but I wouldn't trust them too far.

phew. that was the LONGEST title i ever read.

[galahs]

I fixed it!

I'll write up a detailed explanation a little later. But thanks for the help GSr's.
You wont believe how easy the problem was to fix!!!

[galahs]

This has frustrated me for a while so I'll share the pain and tell the full procedure I undertook to make my realisation.


I knew my floats sealed ok when manually lifted so I decided to find out why my floats weren't floating.

They didn't have a leak and their was no fuel in them.

So I removed the float bowls but left the floats attached to the carbs, 
I then filled the float bowls with methylated spirits, and raised them towards the floats whilst peering over the top of the bowl to see f the floats were infact rising. They weren't!!!


Hmmm, so my floats don't seem to float.


So I removed the float and put them in a container of metho. They floated!


Hmmm, I then submerged the float bowl in my ccontainer of metho so it was slightly submerged, then put the float in the float bowl. It floated!!!

So it seems that the float needs a bowl level just a touch higher than the float gasket to get it to float.

When I emptied the float bowl I thought it was strange that the float bowl seemed to hold more fluid than I had noticed when I drained the floats all these times when checking the level.


BINGO!!!


Something was stopping the floats from filling up enough, preventing the floats from rising. But how could this happen because the fuel is obviously rising up and out of the carb throat.


Wait a second!!!


What if there is an air lock in the float bowl!!!


No way.. it couldn't be!




I then decided to blow down the carb breather pipe.


Ahhhhhhhhhhhhhhhhh! It was blocked!





This would explain it. Both carbs shared the same breather explaining why both sides failed together.




So I removed the breather hose and blow down the breather connection and it flowed.
It ended up the breather pipe had a wasp build a mud nest in it!!!! blocking it.


I cleared the blockage, reinstalled the floats, float bowl for the 1 millionth time then tried pouring fuel down the fuel line.

NO LEAKS!!!!


Ahhhhhhhhhhhhhhhhhh! 





Everything solved!!!




So a simple breather blockage caused all my dramas and was nearly at fault for my death on the road.




I've done a drawing to help people understand what happened for future reference because I don't want anyone going through this heartache. We all take from GStwins and its good if we an all give alittle too!

[galahs]

Here is a diagram explaining what was happening.



The blockage of the breather hose prevented air from escaping from the float bowl as fuel was poured in.



As fuel entered the bowl, the bowl would fill pushing the displaced air out of the jets.

once the fuel level in the bowl reaches the jet no more air can escape from the float bowl. The pressure of the fuel flowing into the bowl however pushes the fuel up the jet into the carburettor throat, then leaks out the air filter.

The current level of the fuel is not high enough to allow the float to rise and shut the fuel supply off.


So fuel just keeps pouring into the float bowl, out of the jets, into the carb throat and out of the air box never allowing the float bowl to fill sufficiently.



After the vapour lock (air bubble) is cleared by clearing the breather, the fuel is allowed to fill the float bowl to a suitable level where the float will rise and shut off the fuel flow.





Here is a picture of breather hose I had to remove and clear a blockage from.

[jsamaniego]

Great documentation! 

Thanks for sharing!!!!  I followed the thread completely clueless... congratulations for your findings 

[galahs]

As Wrecent_Wryder stated, it was going to be some thing simple.

That makes it more frustrating!



It comes back to the old saying, check the simple things first!



And yeah, I put a little bit of effort in my findings to help my fellow GSers who I've learnt so much from 

[Wrecent_Wryder]

T7

[galahs]

the lack of venting caused pressure in the bowls to build up beyond  ambient, so fuel was jetting into the carbs even though the fuel level in the bowls never rose far enough to close the needle valves, is that it?

Yep! Exactly!




My carb breather hose runs to the rear brake side of the engine. I was thinking of putting a filter on it too to prevent this from happening again. For the time being a drilled a few holes in the rubber tube about 2 inches and 4 inches from the exit to make it harder to totally block the pipe.

[drjake81]

Galahs,

I can't believe you solved this problem!!! I've been dealing with the exact same thing for over a year now and have tried all the same tests as you.  My temporary solution has been to install a fuel shutoff valve so I wouldn't empty the tank thru the airbox every time I parked. 

I can't wait to get home and check the carb breather hose... BRILLIANT!!!!

Jake 

[mjn12]

Aaah, I thought I was gonna have a chance to feel so smart.  I once had the same thing happening after dissassembling my carbs. The problem was that I went a little too crazy with the vacuum port caps I bought to replace the cracked ones.  I didn't have a breather tube installed so I saw the open port for the breather and decided to cap that too.  Gas was everywhere.

Then I read on and saw galahs tried this already and it was the magic fix.  Glad its working now.

[galahs]

Damn mjn12, I wish you logged on a few days earlier, you would have saved me many heart aches!!! 

[galahs]

Would you believe I started my bike today and it was struggling to idle.

I straight away checked the breather pipe and it was full of mud!!!

I cleared the mud and shook the hose and a hole bunch (around 15) dead spiders fell out.

Seems we have a local mud wasp that thinks my bikes breather tube is a good place to store the prey he catches.

This made me think I better check my battery breather hose. It was completely blocked with mud and dead spiders too!!!


Ahhhh! Now I'm going to have to put some sort of screen or filter on my breather pipes.

[Joehanson70]

this is very interesting my bike has the same issues im definatley going to try this tommorow

[CrazyDoc]

I'm also super glad this came back up! I am rebuilding my carbs in the morning due to mine pouring gas out of the left carb. I'll check this aswell. What I need is a good picture of how/where to messure the float hight. Anyone have one by chance? i need from where at on the float to where at on the carb body.


Toole

[mimikeni]

So glad this thread was here.  I have been struggling to diagnose my leaking left carb, ever since I dropped the bike in the driveway last week.  I took off the tank, pulled the airbox, checked all fuel line connections.   Everything looked fine.  Put it all back together but the carb is still leaking.  Gonna check several items mentioned in your ordeal.  Could be I buggered the float's functioning when the bike fell over on it's left side. Thanks for your detailed account.  It gives me hope.

[Staysyk]

I'm having a similar problem, I hope this will be quick fix. If a wasp in my breather hose is the biggest issue I have, I"ll gladly evict the fellow and be on my way

[robfriedenberger]

Floats are simple, make sure they float first, if they do than you most likely need to clean the sealing surface and adjust


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[robfriedenberger]

I missed the rest of the thread sorry nvm my response


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[cloudkat]

THIS is a PERFECT example of the power and usefulness of online forums.
A a 7 YEAR OLD THREAD can, and is, still helping people solve their problems.
Short version; my project bike had this EXACT same issue....and it was after reading this that I found out it had the EXACT same problem as well.
See... the internet is good for other things besides porn.