Two Q's re: bing rebuild

[nhlkats]

Good afternoon comrades,
The BINGS on my R100/7 were long overdue for a rebuild. RT cylinder was fouling plugs and also wouldn't respond to mixture screw adjustments. Not to mention the overall "nast" of both carbs.

So I ordered the rebuild kit and started the adventure for the 1st time.

Other than receiving not-matching jet needles with those that were in the carbs before (the new ones were longer -- which begs the question, was I shipped the incorrect ones or was I running incorrect ones this whole time? a paradox), the rebuild went very smoothly.

1st Question
When looking at a carb off the bike (throttle cables not attached), in re: to the throttle stop screw, butterfly position, and the two tiny holes in the venturi: Butterfly fully closed, the two holes are not visible. Couple of turns in of the stop screw and the 1st hole is visible. Where should the butterfly be positioned in relation to these two holes at rest/idle?

I guesstimated the above, finished the rebuild. Threw the carbs back onto the bike.
Oorah.
The right side carb now responds very well to adjustments.
Dang...the left side does not respond to mixture screw adjustments.
I'll lean the left all the way in and the cyl doesn't even complain, chugs away as if it wasn't leaned out at all.

So fuel is leaking in somewhere internally. Took the carb off, took it apart, compressed air, reassembled, back on the bike, not better, took the carb off, took it apart, rinse wash repeat 3X.

2nd Question
If the mixture screw does not affect the cylinder, and the o-ring is intact and correctly placed, and the spring and mixture screw seem to be OK, what could be the culprit. I suppose a quick check is to switch the RT side mix screw with the LT side one, and see if the problem changes. But lets say that doesn't change anything. Where could fuel be seeping in from?

Thanks for your time.

[kbasa]

Did you get the enrichener back in the right way?

Also, is the float level set right?

[nhlkats]

The choke housing and its components were my 1st guess too. Unfortunately I installed it correctly.
Float level is acceptable.

[20774]

You didn't say, but did you take the butterflys off the shaft? If so, getting them on the correct way is very important.

Other than that, when I've heard of this situation, it's usually something wrong with the idle circuit - debris, plugged port, bad o-ring. I had the same problem on my /7...the idle mixture didn't make any difference when I went to synch the carbs. I knew the o-ring was shot. I rebuilt the carbs a few months ago...problem gone. I also used some silicone on the o-rings on assembly so they wouldn't tear up when I ran them in.

As for your first question, I've never heard about setting the carbs that way as part of the initial settings. I usually go by the Bing book initial turns and let the carb synch process figure out where the final settings should be. Generally, using the nominal settings should get the bike to run...there's a broad enough range to allow it to start and run, maybe not great, but it should start.

Note that the idle circuit is a gas circuit...screwing it in makes it lean, out makes it rich. If you turned the screw CCW a bunch of times expecting it to lean out, you only made it richer. Not sure if that's a problem for you...

Kurt in S.A.

[nhlkats]

I did take the butterfly off the shaft inorder to replace the o-ring on the shaft & clean. I made sure to install the butterfly back in the same way it came out. Operation of butterfly and throttle shaft are acceptable.

I will try switching the mix screws. Just to be sure its not the o-ring or mix screw itself on that problematic carb.

When I said "lean it out all the way" I meant "tighten mixture screw CW". Wouldn't it be nice if that were the problem?

I'm "leaning" () more along the debris / plugged port at this point. But then again, I have thrown carb cleaner and compressed air at it several times with no results...

Thanks for the suggestions.

[20774]

What about the float bowl? That well on one corner of the bowl is what feeds the idle circuit, I believe. Make sure that's clean as well. Some of those passages through the carb body are difficult to get to...hopefully you can confirm they're clean.

As for the butterflys...I've never taken mine off yet...too chicken I guess. But on my recent rebuild I noted that the "dot" stamped into the butterfly was on the top half on the engine side. Is that how yours were?

Kurt in S.A.

[26667]

I, too got a rebuild kit from Bing last week w mismatched jets. They sent a 2.66 and a 2.64 instead of two 2.64's in the kit. Everything else was correct. what's up w those guys? Nor do they seem in very much of a hurry to correct their mistake. If they're in today, that's a like a week and a half to mail a part from NE to IL.

Do they not care because they're the only game in town? Or is it an unusual error and coincidence, because they're a small outfit? ...Not that it matters, i suppose. I don't mean to write something negative about them w/o being fair.

[The_Veg]

FWIW, a few years ago I called them to order their overhyped manual. They talked me into buying a set of jets which I now know that I don't need at all, now that I've learned how to tune my carbs.

[sgborgstrom]

BTDT
The butterflies need to seal evenly in the cylinder. It doesn't take much of a gap to take the idle circuit out of the equation- fiddling with the mixture screw won't do anything.

Take the carb off and hold it up to a bright light, I bet you'll see daylight. Then back off the screws holding the butterfly to the shaft and check the gap as you tighten them up.

[RandyB]

FWIW, a few years ago I called them to order their overhyped manual. They talked me into buying a set of jets which I now know that I don't need at all, now that I've learned how to tune my carbs.

Don't get me started. Get the manual, then tweak before buying anything else.

Check the mixture screws to make sure the tips aren't dented or worn. If they are, you'll never get it set right.

sborgstrom is probably right. Make sure you back the idle screws off all the way.

After loosening, you man need to snap the shaft against the spring tension to move the butterflies more easily.

[bobh41]

Was very positive. I got the right pieces with the rebuild kit. I got everything I needed to do the rebuild - manual, Twin Max syncer and a few other bits. My problem included an unrealized set of mice nests in each carb - which really confused me.

The short version - I couldn't get the R90 to idle down. Between a Bing consult, and my local ace mechanic we deduced there was an air leak in there somewhere. I dismantled and reassembled the carbs about 4x before giving up and taking it to the shop. He discovered I had replaced one of the diaphragms 180-degrees wrong, thus the air leak. I swear I studied those carbs with a 6X lens over and over. My point - many of us tend to follow the same logic, or ill-logic as it was, repeatedly in solving a problem, and if we happen to introduce a flaw it's pretty difficult to see past it.

When I stopped back by to check it out he showed me that it now idles okay, but backfires with a twist of the throttle. I've authorized him to go ahead with a new carb rebuild if he finds it necessary, but we are agreed that he is probably dealing with an ignition issue now.

BTW I feel plenty stupid about the diaphragm error, but since this is my first shot at getting this 7-year neglected Airhead back on the road I feel a little smarter handing it over to a competent experienced mechanic.

The downside is I'm learning that Airheads take a fairly low priority in the service lineup - something to do with training and experience of the maintenance staff.

[nhlkats]

Daylight was seen! But nothing could be done about it. I was not able to get rid of the gap, the butterfly will not seal all the way to shut out light.

[RandyB]

I don't think you can eliminate, just reduce it and get it as close to the same on both sides as possible. This assumes that the butterflies are installed correctly.

[Polarbear]

Done dozens of these and "everybody", including ME, can fail at a few items when rebuilding these. TWO things are; the butterflies have BEVELED edges and absolutely "must go back" in with the beveled flat edge against the walls of the body and two; the choke mechansims can be reinstalled 180 degrees out and the problem will be near impossible to see when the carb is back together. These two items are frequent mistakes that can be easily made The needles can be longer indeed, if the old ones were worn down, but two different new ones is a no brainer! Putting in diaphrams backwards is near impossible, if paying attention to the indents in the body of the carb.
Your issue seems like one of the two above mentioned items. They are soooooo simple, but soooo easily done wrong and when you find it, you'll agree. Another thing is the stack above the main jet can go in backwards too, so check your pics for correct stack around the needle, above the main jet!
H appy Trails, Randy13233

[nhlkats]

Thanks for the advice. Unfortunately I've checked all of those items today and they are installed properly.
Today I disassembled, checked to make sure choke piece with the teardrop was not inverted, it wasn't, tear drop on top. I was working with the butterfly and throttle shaft today, trying to minimize that gap as much as possible. The dot is on the top facing the cylinder. I've noticed that if you don't put the butterfly in *just* right, when you put on that metal bracket that holds the throttle spring, and then try to operate the throttle shaft, it will get very tight and won't close or open all the way, and will get stuck. I noticed this can be avoided by properly placing the throttle shaft before putting the butterfly back in.
As for the jet needles, the new ones were substantially longer, not just a little bit.
The nipples of the diaphragm are installed properly.
As for the atomizer and needle jet, I have the atomizer sitting on top of the needle jet, so that the part of the atomizer with the holes is on the bottom. I don't think it will fit the other way around.
Double checked and cleaned all the other passageways, idle jet, etc etc...

Either I am messing up something very simple, or this is a more complicated problem such as debris stuck in the idle passageways somewhere that won't clear with carb cleaner and compressed air.
Tried switching the mixture screws too, but that did not change the behavior of either cylinder, thus the problem is elsewhere.