Elementary question - leaky carbs

[Major Softie]

GIRL FIGHT!

[Chuey]

Now, back to our original programming:

I checked the floats and they float in water. The needles were fresh and pink - no cack of any sort and no signs of anything that could cause a problem.

The carbs still leak. When I turned on the gas, as soon as the float bowls filled, they started to leak. I'm asking this question to check and see if I understand what is going on in there. When the bowl fills, the floats should rise, pushing up the needle which should seal the seat and that should stop the inflow of fuel, right? If that is the case, the fuel should be shut off before it has a chance to leak out of the carbs, right?

I'm asking that because I would love it if something as simple as some bowl gaskets would solve the problem.

Repeat of information given earlier in thread so you don't have to go way back to help:

1983 R100 with stock carburetors.
Carbs rebuilt not many miles ago.
Bike sat for nearly a year.
Bike started and ran fine. That was with carbs leaking.
No cack in carb bowls, carbs look very clean inside.

Thanks for the help. It may seem like I don't understand much and have to be led through this but that is only because that is the truth.

Chuey

[Garnet]

With the bowls off, hold up the floats with your finger, and turn on the gas.

Any leaks?

If not, slowly lower the float and observe when fuel begins to flow. It should be when the seam in the float is parallel with the carb housing.

I think this was posted earlier here somewhere.

Edit: One carb at a time.

[Chuey]

Thanks, Garnet. I think it was posted that I could put more pressure on the needle by holding up the float than could the floats when they are trying to shut the flow. If it was said earlier, I missed it or didn't understand it. I can do what you instructed tomorrow. I'm off to work now.

Chuey

[Garnet]

I should have said as well that there should be a very clear on/off point at that parallel point. You should not have to hold the float up with any force. This tells you that the needle IS seating.

It does not tell you if your float is too heavy. The only way to check that is by measuring the level of gas in the floats.

To do that, you turn on the gas with the bowls in place. Clamp off the gas line as close to the carb as possible. Remove the bowl, and measure the level. It should be about 2/3rds full. There is a number out on the inter web, I think it's about 19 or 20mm, but I cant remember. The most important thing is, that both carbs have very very close to the same level, and the gas doesn't spill over the top of the bowl when first removed from the carb.

If you have the flow stopping when the float seam is parrallel, and a lot of gas spills from the bowl when removed from the bike, then the float is too heavy and sitting to low in the gas.

[Garnet]

One more thing.

Even when the level is perfect, the gas is at the top edge of the front of the bowl because the carb is at an angle, more so when parked on the sidestand. As mentioned earlier, good bowl gaskets and mating surfaces are a must, and very often the culprit.

[Ken in Oklahoma]

But just in case.

Once upon a time I was chasing my tail trying to fix a leaky carb on my '77 S bike. By then I had learned some things about leaky Bing carbs. I had done the usual things, new needles, examined the seat, and I had even learned that heavy floats will cause no end of problems. But this time I was totally vexed. I had the carb bowl off and in desperation I was checking the needle and seat by manually lifting and dropping the float, this time with the fuel tap on. Incredibly, even while holding the float up with my fingers I still had a leak. Impossible, but there it was. Gas was dripping down that little do dad that goes into the hole in the float bowl. How the hell could it be leaking there?

Eventually I finally figured out the impossible leak. It was another self-inflicted injury. It turns out that my fuel line was old and had developed a crack. Gas was leaking from the fuel line and wicking it's way down the carb and dripping from that aforementioned do dad.

I still haven't quite gotten over my error, not out of residual embarrassment, but mostly because Major Softie reminded me of it when I was giving out some of my sage advice about leaky carbs.

Ken

[Garnet]

I still haven't quite gotten over my error, not out of residual embarrassment, but mostly because Major Softie reminded me of it when I was giving out some of my sage advice about leaky carbs.

Ken

Ahhhh Boxerworks!

[Major Softie]

I've burned him on it a couple times - actually just told people with leaks how confounding it had been for Ken when he had that problem.

I didn't bring it up this time because I've been trying to move on.

[Deleted User 62]

Here's a new one for you. The right carb on my '72 had a very slow leak that showed up on the round lip around the vent tube. It would wet the bottom of the bowl, but not drip. After fiddling with the float levels had no effect, I tried swapping a bowl from another carb, and wala nui ho, no more leak! Apparently it was seeping out where the brass tube exits the bowl. I figure either the tube is cracked, or somehow got loose...