Full circle season w/ carb

[Deleted User 287]

I happen to like the braided fuel line, so I am willing to replace it every 3 years as a maintenance item.

Yes, I had one leak on me, once.

Not since.

[Major Softie]

That fuel line may be one of those many things that are affected by alcohol in the fuel. It seemed to last longer in the past than it does now.

[lrz]

'lo all-
The fuel line is not the culprit as gas is originating from the overflow-to be sure, however, I switched in a newer length from the T to the carb. Same result.
Upon further investigation, I am suspecting the new float itself. Whereas the flow of gas was shutting off immediately after it's installation last Spring, I believe the new float has sunk a bit and have re-adjusted the tab accordingly.
The needle,also replaced,now has a uniform ring (slight groove?) just below its tip and, to the eye at least, the seat looks normal...just returned from perhaps the season's last fill up, treated w/ Sta-bil marine, petcock is off,kitty litter beneath the carb...
NO JOY! Last evening @ 6pm no leak, by 5:30 this a.m. the aforementioned kitty litter was wet.

[lrz]

This has been eating at me so last evening I installed a new, unused float as well as a new float needle. After tab adjustment ,the gas flows to the appropriate level & stops when petcock is turned to off. I verified this by emptying the bowl, checking that it remained empty a few times until 10:00 pm or so leaving the petcock off only to return this morning to find the contents of the the fuel line from the petcock down in the float bowl.
So, that is TWO new floats, TWO new float needles w/ the same result. Does it seem the only remaining culprit IS the seat?

[ME 109]

New needles fixed my leaks for a short time.
I even had the 'damaged by me' seats machined a little to see if it would stop the leaks.
The only thing that fixed my leaking carbs was new seats.

I don't know if your seats are the problem or not.

[dwire]

OK, I'll bite...

I have rebuilt likely well over 10,000 bowl type carburetors - only really recall replacing a seat due to a unit NOT BEING USED... (If I remember right, the last was a vintage nearly century old Clinton carb that was dug out of the Earth and placed in my care...) That being said, I have rebuilt only two pairs of BMW R75 Bings. I read and re-read your post. All that is here is good sound advice.

My thinking is this; since these use metal needles that are easily inspected (not the Niflon or other rubber ended jobs IIRC...) than if you are really certain the "interface" is opening or leaking and know it is not because a sinking float or mis-adjustment "told it so" than I would look to the seat replacement earlier in the year as the culprit; something easily cocked and screwed up. Perhaps if you can find nothing else, think of checking its geometry, something pretty tough in that little hole. I generally use a special type of "putty" for these sorts of things. Sorry, the special tools are burried at the moment, or I would give you a manufacturer (also brain is failing...)

Why were the PITA seats ever replaced? Others can weigh in that have specific experience with their wear in this application, but I can't imagine why; unless the bike was not in service, which it seemed to be... It is amazing that needles wear in a sense. 99.9% I've replaced never needed it; it came with the parts (could be why they "never needed it" - they were getting changed often...) but seats generally if left in service or are not somehow left out to rot, should outlive most riders, all but the multi-million mile "iron-butt" club perhaps. Besides, the vast majority of carbs I've done, the seats were not replaceable at all and they both saw more cycles (from the needle) and more hours than any motorcycle is likely to...

EDIT---> The rubber type Niflon and other compound-ended needles were much more prone to wear than any steel needle ever thought of being. Some of the old Tecumseh's were coated with a thin green coating to make them not only easy to see how the match up was, but if they needed replaced; as the green wore off to black in a wider band, they were on their way to needing replaced. So above I should have specified as well that the high 99.9% statement, while likely true, with the giant amount I saw for the reason mentioned, the steel, all metal type such as is installed in the Bing CV's were a rarity to truly fail.

Good luck with your endeavor!

[ME 109]

If there is a 'score' down the side of the bore that the seats are pressed into (from a botched prior seat removal), fuel can pass down the outside of the seat, bypassing the needle, resulting in an incurable leak....

[dwire]

So true Mr. Messerschmitt 109... Good call.

[lrz]

Seats themselves appear fine, meaning unscored & original; new float needles have viton tip. Any reason that newer tip should not work as intended w/ original seats? What I just don't understand is why the leaking began suddenly after very few, less then 1,000 mi, this season.
I'd prefer not to endeavor replacing seats needlessly, as clearly things have the potential to go wrong during the process, but having replaced all other components twice at this point cannot think of another culprit.

[dwire]

EDIT---> More productive likely to read the next post... Thanks!


Oh, boy my memory is fading Sir, sorry about that. I thought I recalled my Bing kit(s) coming with solid steel needles and not Viton, Niflon or any of those other trade names of silicone/rubber ends...

You truly have me at a loss. From all you have done which seems to me you have covered all the bases correctly, - what, could it be your imagination??? Sometimes we run into these things. All I can say is you will find it and since it seems you've done a thorough job trying to properly diagnosis it, it will likely be something utterly simple, so obvious it gets overlooked, or I find that to be the case often in my work... Sorry I am of no help. I have had those "rubber-ended" needles be bad out of the box, but that was pretty rare. Are you sure the float is not binding? What about the level of the carb when it is mounted??? Sorry, I'm as lost as you here...

I see you mention the seats are original, didn't you post they were replaced once after the bowl-loss incident, or did I misread that? It has been several years on my last Bing CV, and I don't remember the interface on the float being something prone to binding. Don't they have the steel clip (just a thin wire "thingy" attached to "capture" the needle on the float tang...) on them, or are they "bare?" I've seen those hang up on things before. Also, are you 100% sure, no binds in the float and its level is really correct???

Gee, sure hope someone else has better thoughts, for taking you at your word on all that was done and checked, I am stumped. OH, hey, is the gas coming from an actual over-flow? I recall pulling something and re-epoxying it in; some sort of drift? Don't recall where it's at or leads to. Sure it was there for access during the machining process, I'll run out and look. I think that was on the body though, not low enough to spill fuel from simply a correctly filled bowl.... Hmm..

It (the carb) is mounted level, right?