Full circle season w/ carb

[lrz]

Greetings!
Waaaaaay back in the Spring, March, & before the newest forum, I began the riding season w/ my left carb bowl falling off mid-ride. Found the bowl but not the float needle; subsequently replaced both float & needle . Seemed fine all summer -though riding time was limited. This weekend I noticed the smell of gas and, sure enough, left carb has leaked the line from petcock down dry. Now, assuming the new float is not somehow defective (sinking), and knowing it was shutting off fuel flow,as well as having blown passages clear,I'd guess it's time for a new valve seat.
Have searched, doesn't seem an easy repair on these 40mm Bings. Any experience w/ this? Or perhaps something I've overlooked?

[Deleted User 287]

If you are using the original cloth-braided line, how old is it? Depending on many factors, it could be leaking.

[lrz]

IIRC the line is 4yrs -ish...what are you thinking ,air leak creating a vacuum? Having read snowbum's mention of replacing the seat over the weekend I am more than open to alternative approaches.

[Dave Backmarker]

I'm not too familiar with Bings having the pleasure of rebuilding my Dellortos. But, as noted in this forum, the floats in the Dellortos (new floats) are affected by ethanol in the gas. A sticky float would drain the line from the petcock as it would not move up against the needle to shut off the fuel flow. I had this happen to both carbs. Simply removing a tiny amount of plastic has them both working fine. Does the float move freely on its hinge? NO noticeable sticking?

DaveM
1975 R90S
2000 R1100RT

[Airbear]

Lrz, it could just be a bit of 'something' temporarily catching between needle and seat. It happens to mine occasionally - I just pop off the bowl, let the float hang so a good mouthful or so of fuel runs out, then gently push the float up to see if the flow cuts off where the float is parallel to the carb body. That generally fixes it and I'm good to go. If it doesn't behave, the next thing to do is replace the needle. It's kind of rare to damage the seat, I gather.

[vanzen]

Lrz, it could just be a bit of 'something' temporarily catching between needle and seat...
- I just pop off the bowl, let the float hang so a good mouthful or so of fuel runs out, then gently push the float up to see if the flow cuts off where the float is parallel to the carb body. That generally fixes it and I'm good to go...

Easy items first, and this will be the place to start.

ONE single grain of sand will cause a carb to flood & overflow – don't ask ...
A miniscule bit of that red tank-liner (after a larger bit dislodges the screen and tubes in the petcock)
will cause a carb to flood & overflow – again, don't ask ...
A tiny speck of 4 year old brittle BMW braided fuel line will cause a carb to flood & overflow – BTDT.


Often, evidence of any such sediment will remain in the bottom of the float bowl as a clue.

[ME 109]

It's kind of rare to damage the seat, I gather.

Oh yee of little faith, you're forgetting my abilities, I damaged my seats quit easily. (with a drill bit )
What does Bing know about aperture size anyway.....

The seats are available from Bing USA.
I changed my seats with minimal fuss using GSPD's method.
Quite simply, tap the damaged seat with an 8mm x 1mm tap.
Make a simple sliding hammer that will screw into the now threaded seat.
Heat the carb body immediately around the seat with a small propane torch and use the slide hammer to extract the seat.

Put the new seats in the freezer before heating the carb in the same place again and tapping the new seats into place.
Gotta be quick as the seats will warm and the carb body will cool quickly.
A little oil/grease on the new seat will help.

GSPD was emphatic that this method was the only way to do it, otherwise the sh!t will hit the fan. I must agree.

[lrz]

Hey-
appreciate the replies. As mentioned, float and needle were replaced as well as flushing w/ needle removed & gas flowing; tank was Kreemed by PO ,btw. Tank flushed & dried, petcocks cleaned and new screens installed as well. I do understand it is unusual to have seat damage during normal use and, frankly, hope to discover some other issue.
As the riding season draws to a close here, this goes on the winter maintenance list ...we'll see.

[Ken in Oklahoma]

The fuel line has already been nominated as the culprit, but I want to add more emphasis.

A handful of years ago I chased my tail for days on my '77R100S with the 40mm Bings. I focused on the usual things, heavy float, mal adjusted float level, crud in the fuel line, bad needle, or damaged seat to no avail. The symptoms were clear, fuel tap on gas was leaking into the bowl area, fuel tap off, it didn't. Pushing the float up and down didn't change a thing.

Ultimately, in the process of fiddling with the float, seat, needle I accidently discovered the problem. It was a crack in the fuel line, just above the carb inlet spigot. What I thought was gas leaking into the bowl area was gas running down the carb body and then wrapping itself around the carb housing, and then dripping down the long thin brass tube that goes into the vertical tunnel of the bowl itself. The fuel line, automotive 1/4" fuel line, looked good and I couldn't remember when I replaced it, but it seemed a short time ago. Simply, the fuel line wasn't on my radar as a potential culprit.

What got me into the jam had to be overconfidence. I had worked on Bing carbs several times and knew pretty well what went on inside of them. I was confident that with the symptom so clear that I would have the carb leak fixed with little effort.

Ken

[barndeadr80]

I had leaking fuel lines that were fresh and new cloth covered BMW lines from less than 3 years before. Loose fitting and cracked where they pushed on. If it sat a while, the bike's float bowls took a while to fill. New lines, much improvement.