Carb leak

[Guest]

Hi guys, first post having lurked around for far too long and soaked up lots of info!
Restoring a UK GSX1100EZ (I think same as US GS1100) and rebuilt the carbs as described in the brilliant tutorial downloaded from Basscliff's website and using the recommended o rings etc. there.
All went well and before putting carbs back on the bike I set them on the bench with a dummy tank overnight to make sure nothing leaked.
All was well for about 4 or 5 hours so left overnight to find a small damp patch under one of the carbs.
Tried to find the leak but can't see anything obvious, other than a small amount of petrol sitting on the lower fixing rail around the leaky carb.
I wondered whether this could bedue to the petrol being on for such a long period of time i.e. without the vacuum tap etc.
Or should the floats seal completely irrespective?

Cheers for any help
Andy

 

[hampshirehog]

A few things spring to mind:

Are the valve needles in good nick? If you can see a ring (use a magnifying glass) they might not be. A decent test (though not infallible) is to turn the carb upside down and try an blow though the closed valve. Could be a hair or something tiny also blocking the needle from sealing completely - see thread concluding with Roeme's beard!

The o rings, especially in my experience on the link pipes, sometimes need to sit in petrol to seal. If they've sat drying out try your test again and see what happens.

Just to check, you did change the o rings on the needle valve seats?

Float pin could be bent. Difficult to spot but try turning the carb upside down slowly (bowl off) and see if it sticks.

 

[Nessism]

If the float needles are original or aftermarket they most likely won't hold back the gas for hours at a time. I don't think that is a realistic test.

And when you set the float height did you measure the fuel height using the clear tube method? Doing so is critical to assure the fuel level is correct. Setting float height is just an approximation to get the fuel level in the ballpark. It's not definitive in of itself.

 

[Guest]

Thanks Guys,
I originally used new valve seats and needles and jets from a rebuild set but after reading here went back and checked / cleaned the originals and refitted those as it sounds like these are better quality in general.
All parts looked fine and just had to swap out one pilot jet that was blocked and looked a bit beaten-up. Luckily have two spare sets of carbs so could use an original replacement there as well.
All O rings replaced as shown in the tutorial and floats and pins OK and moved fine.
Set the float heights so I'll check them with the clear tube method later as well.
Looking at the carbs it looks like the fuel is very slowly forming and coming out through the airbox / exhaust main openings so I guess this is indeed fuel slowly getting past the float valves.
I wasn't sure how much / long the float valve would hold back fuel when effectively on prime setting - they stayed dry for a good few hours so maybe it's just an unfair test of the carbs.
Before refitting I just wanted to check as much as possible as removing / refitting the buggers is such a pain.
Cheers,
Andy

 

[Guest]

Back again,
Went through the float heights etc. again and used the clear tube method to set all 4 to the right height.
When first filling, they all settle at the correct level which is pleasing.
Set up on a dummy tank so no vent tube etc. and after several hours one carb started to overflow and I noticed they all settled a bit lower down the tube then when first filled.
I just wondered if this is normal as when connected to the tank they will be on the vent setting etc. or do I need to look further at the needles / floats etc.
Cheers again,
Andy

 

[hampshirehog]

If they're taking hours to overflow and not minutes there's nothing to worry about.

 

[JTGS850GL]

Almost all of the carbs will overfill over a period of hours. Not an issue. It's why they have a vacuum operated petcock. Once the bike is running there is a constant amount of fuel being consumed and the valve will open/close. Mount the carbs and move on.

 

[Guest]

Thanks - back on they go!

 

[Steve]

One more question, just out of curiosity: how high was your test tank? :-k

Ideally, it should be about the same distance as the stock fuel tank. If it is too much higher, there could be enough head pressure to force the petrol past even the best float valves.

.

 

[Guest]

Sorry for delayed thanks again.
I made up a timber frame to hold the carbs level and fix a temporary tank a foot or so higher than the carbs which worked really well for setting the float heights.
Fitted carbs and bike ran pretty smoothly straight away - synchronised carbs and now runs really well for the first time since being deserted in the PO's garage in the eighties.
Put all the shiny bits back on and have run the engine a few times and ridden up and down the drive and all seems really good so hopefully she's now pretty well 'finished' with a bit of final fettling.
Thanks to everyone for advice on this
Cheers,
Andy