Float Bowl Still Leading

[rickt]

I think the number of carbs on my '78 GS750C that are are still leaking gas from the float bowl vent hose is now down to one - actually carb #1. I removed the bowl this afternoon and turned the petcock to prime. As expected, gas flowed and when I manually raised the floats the gas flow stopped. I really don't think that the bowl is interferring with the movement of the float. What else should I look for to stop the leaking gas? I set the float height when I rebuild all four carbs. If I missed the mark on carb #1, would this cause the gas to leak? Can I measure and adjust the float height with the carb rack on the bike?

Thanks for any suggestions.

rickt

[49er]

I think the number of carbs on my '78 GS750C that are are still leaking gas from the float bowl vent hose is now down to one - actually carb #1. I removed the bowl this afternoon and turned the petcock to prime. As expected, gas flowed and when I manually raised the floats the gas flow stopped. I really don't think that the bowl is interferring with the movement of the float. What else should I look for to stop the leaking gas? I set the float height when I rebuild all four carbs. If I missed the mark on carb #1, would this cause the gas to leak? Can I measure and adjust the float height with the carb rack on the bike?

Thanks for any suggestions.

rickt

First, check the condition of the float needles and seats. It may be time to fit a new set. Next, check that the float isn't punctured. It could be damaged and taking in fuel causing your problem. Not sure if your model has brass or plastic floats. I am assuming that you did verify the accuracy of your float heights first.

It's extremely difficult to work on the floats while the carbs are still on the bike. Take them off again, before you do some damage.

[rickt]

Everything is new

Needles and seats were all replaced with new pieces. Carbs were stripped and dipped. I don't think the floats are hollow and yes, I did verify the float heights before everything was put back together.

rickt

[49er]

Needles and seats were all replaced with new pieces. Carbs were stripped and dipped. I don't think the floats are hollow and yes, I did verify the float heights before everything was put back together.

rickt

OEM new, or aftermarket new needles? Some kits supply needles that are the wrong length, so you don't get the correct float levels by using factory settings. It may be necessary to check them again.

Needles, damaged floats or incorrect heights are the only likely causes of your problem. A petcock failure would cause this affect but usually across all the carbs. Also, the #3 pot would fill your crancase with fuel, on your model.

[Nessism]

If you have rust in the tank it will foul the needles pretty quickly even if you cleaned the carbs. Not sure this is the problem but worth mentioning.

[LarryA_Texas]

I think the number of carbs on my '78 GS750C that are are still leaking gas from the float bowl vent hose is now down to one - actually carb #1. I removed the bowl this afternoon and turned the petcock to prime. As expected, gas flowed and when I manually raised the floats the gas flow stopped. I really don't think that the bowl is interferring with the movement of the float. What else should I look for to stop the leaking gas? I set the float height when I rebuild all four carbs. If I missed the mark on carb #1, would this cause the gas to leak? Can I measure and adjust the float height with the carb rack on the bike?

Thanks for any suggestions.

rickt

Had a similar problem with overflow. When I opened them up I realized that the float needles seemed to fit properly, but would not rotate in the seat. Not that they need to, but what that indicated was that the seat was slightly out of round and if the needle rotated slightly while running it would stick. The seat might have been damaged while pulling it out or putting it back in. Make sure the needles can move freely in there.

[chef1366]

Is that the float bowl at the front with the flag and paton?

[49er]

Is that the float bowl at the front with the flag and paton?

Hey Bill, I see you're getting bored again. How about some new mods to that 1100L ?

[chef1366]

Hey Bill, I see you're getting bored again. How about some new mods to that 1100L ?

Nah, done with that.
Building a Yellow turd dragbike.
No pods but with velocity stacks!

[robertbarr]

Needles and seats were all replaced with new pieces.

What is the source of the replacement needles & seats?

For many people, the problems begin when they install parts from rebuild kits.

That said, I've never been able to visually find a flaw with a leaking seat / needle combo. I'm not sure why, but I've scrutinized known-leaky seat/needle combos and they look fine. No visual clue as to a cause. Replacing them with OEM solves the problem.

[rickt]

Carbs are coming off!

The carb rebuild kits came from Sirius Consolidated, Inc.

Carb 1, even with extensive tapping, rapping, cursing, and intake of alcohol (by me not the carb) continues to leak from the float bowl vent.

I'm gritting my teeth and pulling the carbs. I'm not quite sure what I'll be looking for? My plan is to remove all four float bowls and check the float height first.

Is my assumption correct that the proper method for checking float height is to have the carb "upside down" with the needle fully seated, then lower the float until the tang just contacts the tip of the needle? Then measure the distance from the bottom edge of the float to the float bowl gasket surface (minus the gasket)?

I'm tempted to replace all needles and seats with new parts, but my search of parts fische suggests that OEM are no longer available.

What other vendor options are available if I decide to replace just needles and seats?

How should I go about bench testing for leaks once everything is back together? I'm thinking that I'll set the carbs on a bench and connect the gas line to an axillary tank and see what comes out of the vent? Does this make sense.

If there are other ideas on how to resolve my problem, I'd love to hear them!

Thanks,
rickt

What is the source of the replacement needles & seats?

For many people, the problems begin when they install parts from rebuild kits.

That said, I've never been able to visually find a flaw with a leaking seat / needle combo. I'm not sure why, but I've scrutinized known-leaky seat/needle combos and they look fine. No visual clue as to a cause. Replacing them with OEM solves the problem.

[chef1366]

When you measured the floats with it just sitting on the valve how did you measure and hold the float perfect. That's kinda hard and get it right.
What I've noticed about aftermarket needles is that the spring in the valve is weak and depresses too far with just gravity pushing the float down and the valve goes in at least half. This to me makes it almost impossible to set a correct float heigth. See if K&L makes a kit for you. They are the lesser of the evils of other kits.

[twiggy2cents]

swap a float needle/seat while your in there for verification

[rickt]

Update - Leaking Float Bowl

Pulled the carb rack this afternoon and took a close look at #1 after removing the bowl. Everything looks good: float height at 23 mm, no interference with bowl gasket, needle moves easily in seat, spring in seat ok.

The only thing I noticed was that the float pin slides easily in the mounting tangs. Is this a problem? I'm pretty certain that the other 3 were interference fits and had to be "tapped" in.

I ordered two rebuild kits from Z1 - I really don't know what else to do. This part of the carb is (or should be) pretty dog gone simple.

Am I missing something really obvious???

rickt

[robertbarr]

The only thing I noticed was that the float pin slides easily in the mounting tangs. Is this a problem? I'm pretty certain that the other 3 were interference fits and had to be "tapped" in.


Am I missing something really obvious???

rickt

With or without an interference fit, the bowl itself will hold the pin from sliding out. Examine how the bowl is shaped and you'll see (and you probably already have...).

You have a bum seat / needle combo. It's unfortunate that many rebuild kits are of such poor quality.