Leaky Carb - What to do Next

[SteveD]

Maybe this by me 109?

https://forum.boxerworks.com/viewtopic. ... 678#p24678

Kurt

BING-o That's it. Thanks Kurt.

[Jeff in W.C.]

Here's an update. I ordered a new float needle and gave it a try with the newer float and switched float bowls. It leaked within 10 minutes. So, I switched back to the original float bowl and switched to one of the older floats. After 20 minutes, no leak. Figured if I went another 20 minutes with no leak it would be solved. I decided to go inside after an additional 5ish minutes (25 minutes total)--it was dry at this point, BTW. Went back outside after 35 minutes total and it had a slight leak--damn. So close. Moving in the right direction though. So, what should be my next course of action? Should I order a new float, or send it off to Bing for their diagnosis?

I'm tempted to swap the jets (main, idle and needle) over to my back up carb just to get the bike up and running again. FYI, my back up carbs are jetted to stock, while these are re-jetted per Bing's recommendations for later model R100's.

[Jeff in W.C.]

I swapped the float and float needle from the leaky carb to my back up carb, and everything was leak free. So, out of process of elimination, it has to be the float needle seat. I figure if one seat is bad, the other one is close, so might as well do both. According to the PDF of Bing's in-shop services, replacing both float seats is $80, which includes parts and labor. I just need to pay for shipping. That's a bargain in my book; however, the price sheet is from 2024, so prices may have increased a bit. These carbs are expensive to replace, so I figure it's better safe than sorry and have the seats replaced by those who do it regularly. I will be calling Bing tomorrow.

[Rob Frankham]

Be interested to hear what the result is...

Rob

[Jeff in W.C.]

After describing what I've done so far, the recommendation is to replace the seat. Since both carbs of the same vintage and mileage, it was recommended to do both. It was suggested that if I'm handy to replace them myself. The person who does this is not located in the state of Colorado like Bing is. They are located in the state of Kansas. He thought the prices went up a bit from the price sheet online, but recommended I call the individual who does the work. That call is tomorrow.

[SteveD]

Good progress. Sounds like you're almost there.

[SteveD]

I read this on fb today...difficult to fix leak despite all the usual interventions.

I ordered and installed a new float and needle. Same leak. I adjusted the float to seal at a lower point. Same leak. It was obvious to me the seat must be bad but even very close examination didn’t reveal any problem. Then I had an idea.
I removed the carb again, took out the new needle and put the OLD needle back in place. I then took a light hammer and GENTLY tapped the needle several times while rotating it between taps. I then reassembled the carb, reset float height and reinstalled it on the bike.
I’m happy to report that after two hours and a few start stop cycles the carb has not leaked a drop. Before, I would have had a foot wide puddle on the ground within half an hour.
The needle is steel, the seat is brass. I believe that my method swaged out any imperfection

Maybe something harder than a pencil lapping the seat could achieve a similar result? Hammers are HD tools aren't they

[barryh]

The needle is steel, the seat is brass.

Was that FB post talking about an airhead of the same vintage as this thread ?

Surely the needle should be rubber tipped.

[SteveD]

The needle is steel, the seat is brass.

Was that FB post talking about an airhead of the same vintage as this thread ?

Surely the needle should be rubber tipped.

75/5.
Here's the whole post:

Leaking Bing Needle Seat; Easy fix!
I’ve been rebuilding carbs for over 50 years. Today this old dog learned a new trick. The bowl vent tube would drip continuously from my left carb if I left the shut-off open. I did the usual things, I checked float adjustment, cleaned out the fuel inlet and examined the needle and seat. All good. I then reassembled and reinstalled the carb…which leaked exactly as it had previously.
I made absolutely certain the fuel was coming down the vent tube, not leaking from the base.
I ordered and installed a new float and needle. Same leak. I adjusted the float to seal at a lower point. Same leak. It was obvious to me the seat must be bad but even very close examination didn’t reveal any problem. Then I had an idea.
I removed the carb again, took out the new needle and put the OLD needle back in place. I then took a light hammer and GENTLY tapped the needle several times while rotating it between taps. I then reassembled the carb, reset float height and reinstalled it on the bike.
I’m happy to report that after two hours and a few start stop cycles the carb has not leaked a drop. Before, I would have had a foot wide puddle on the ground within half an hour.
The needle is steel, the seat is brass. I believe that my method swaged out any imperfection that there might have been in the seat, much like hand lapping a poppet valve for a perfect seal. Regardless of the reason, it worked and saved me from yanking the seat and installing a new one.
The ‘fix’ was fast and cheap. Give it a try before ordering a new seat.
Be sure you have a new needle valve because you will ruin the spring ball in the top of the old one when you tap on it.
(My bike is a 1973 R75/5)

[barryh]

They weren't always rubber tipped so perhaps not in 73.

Must have been harder to get a good seal when the tip was brass as the seat and valve surfaces would have to be perfect.