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Bing help

YYZED

New member
Hello All,

This July I got a 92 R100R that needed lots of help. I fixed all the electrics and started on the mechanicals after lots of work she is running good, or so I thought. I have a friend with a dyno and strapped it down to get a reading on my A/F ratio. It turned out to be 10.5:1 though the entire rev range way to FAT! I did rebuild the carbs with a Bing kit, all the jets are the correct size and I started at the base settings for the carbs. The starting circuit is built correct, on the proper sides and are adjusted to go fully off. The floats are in good nick and correct height. I could lean it back some with the mixture screw but not enough. I checked and adjusted the valves and the carbs sync well at idle and 3500 RPM and she is getting about 38 MPG. I have heard that the jet needle can wear and cause a rich condition but would it do it through the entire range? Or should it only go rich 1/2 throttle and more with bad needles? The plugs look a bit rich evenly on both sides.

Thanks for your time and help.

Cheers,
Jim
 
Did you replace the needle jets when to rebuilt the carbs? The needle jets do wear, the jet needles wear very slowly.
 
Did you replace the needle jets when to rebuilt the carbs? The needle jets do wear, the jet needles wear very slowly.

I did not replace any of the jets or needles I just put them through the wife's sonic cleaner with DI water. But would those jets affect the entire rev range?

Jim
 
What notch did you set the needle in and did you count from top or bottom? (They're numbered top notch to bottom)

Did you check what size main jet you have? (It has a number on the side). Is it the stock one, or bigger?

Airheads@micapeak.com is a great mail list that could probably help some.
 
I did not replace any of the jets or needles I just put them through the wife's sonic cleaner with DI water. But would those jets affect the entire rev range?

According to the Bing book, the needle and its jet are effective from 15 to 80% of throttle. There is overlap with the idle jet on the low end and the main jet on the top end.
 
I wonder if someone has (or can) relate with some certainty where these "transition" places are (by rpm's or % of full throttle) - from idle to needle, and then the transition from needle to main jet.

The other thing I would like to know would be the exact amount of taper on the jet needle per length of linear travel. With that knowledge, one could calculate the amount of size difference (diameter of needle) at one point, and then figure out the diameter of the needle at another point a certain distance away (like from one "notch" to the next "notch."

Also, is the amount of taper the same throughout the full length of the jet needle? There could be two or three different tapers in that length, but I doubt it.

If I had a brand new jet needle, I could put it on a comparitor and measure it.

It would also be nice to know the exact dimensions of the passageways in both the idle jet, the needle jet, and then the main jet.

I am also wanting to know just how much "wear" (size-wise) on either the needle jet, or the jet needle( or both) there needs to be to actually affect the running of the motorcycle.
 
Bing spends 2-3 pages in their book discussing the needle and jets. They also publish the % overlap...most likely for a standard configuration...that would be all over the map for different carbs, different states of wear I suspect. The main jet numbers are essentially the diameter of the jet in mm. The information you're looking for might be there. :dunno

Magazine articles from the late '70s tried to describe how the CV carb worked.

http://www.omnilex.com/public/bmw78/4.jpg
http://www.omnilex.com/public/bmw78/5.jpg
 
Well Clymer is worthless as far as the 92 R100r settings, but if I use the 1988-1989 it shows the following:

Right hand carb 64/32/358
Left hand carb 64/32/357

Do those match what's on your bike? If so it shows the following:

Main jet : 135
Needle jet: 2.66
Needle jet # 46-251
Needle clip position from top: 3rd
Idle jet # 45

I'll try to look it up in my bing book when I'm back out in shop. (Sign up for airheads list and you'll get great assistance. :) )
 
Those are the numbers from the Bing book for 357/358 carbs. It also suggests the idle mixture initial setting as 0.5 turns out.
 
Hello All,
I checked and adjusted the valves and the carbs sync well at idle and 3500 RPM and she is getting about 38 MPG.

Everything else aside, from what I've read and experienced on my 88 R100 RT, high 30's fuel economy is typical for the mid 80's bikes onward. Very few riders report MPG above 40 for the later bikes. These later bikes to do not get the same fuel economy as their earlier brethren. So, if everything's OK, just ride and enjoy it. Anyway, that's my take on it.
 
Needle jets

I've repaired and rebuilt more than I can remember motorcycle carbs over the years. Other than tired diaphragms and leaking throttle shafts on butterfly carburetors needle jets make a big difference.

Needle jets are made of brass, needles are made of a harder material, mostly stainless but not always. Vacuum sucks them forward so they tend to rub on the forward inside of the jet. Wear there can be just a few 10ths of a MM, with a diameter that small it doesn't take much wear to make them run alittle rich.

On a 20 year old motorcycle there's going to be some wear.

Also the throttle shafts tend to leak air on older Bings so people set the idle mixture alittle richer to compensate. They run ok, they just use alittle more fuel.
 
This weekend I dropped the needle one notch (was on 3 now it's on 2) and it felt much better and my milage went to 39 MPG at elevated highway speeds in heavy winds. So with 55k on the clock I'll order new needles and jet and maybe 2 sets of smaller main jets. I just did not think that the needles made that much of a difference I would have chased floats or the starting circuit all day long.

When I rebuilt the carbs I did check with the Bing book and all parts are the correct # and I set them to the starting settings. I guess if something is going to wear out I'm glad it went rich rather than lean like my RD did, that did not end well.

Cheers,
Jim
 
Replace the needle jets, and the needles if you wish. I wouldn't mess with the main jets until your shure it needs more fuel at wide open throttle.

Do one thing at a time to make shure that corrects the issue. The needle jets are a good start.

You might make shure the floats float. Ethanol in gasoline has been known to wreck plastic floats.
 
I think there are some odd data points here.

I have only ever seen very high 30's mpg (miles per US gallon) on my 23,000 mile 1993 R100R on long lightly-loaded lazy trips. Similar story with my 40,000-mile 1993 R100RT. Typically running errands I see 32 mpg, and short runs around 35 mpg.

On this basis, and depending upon your riding style and journey type, your 39 mpg and the reported A/F ratio do not seem to stack up.

If the plugs are not showing an overly rich mixture, I'd just get on and ride.
 
What speed, dyno load and gear were you running when you observed this rich condition?

Also, after riding, do the finger up the exhaust test. Let it cool, then stick your fingers in there and run them along the sides. If your fingers are full of soot (fully black or chunky), you are running very rich. Lightly coated , skin very visible, is just right and yields good fuel economy. L/R tips should give the same reading.

39 mpg seems reasonable to me. I get 45-49 on my R80RT, depending on what I am doing.
 
Through this post, I was emailed privately and introduced to a person whom I think is a Bing expert, but not personally on this site. He gave me lots of valuable date about needle jet and jet needle.

But the most valuable to me, however, was his advice to look at throttle position when riding. Most of us rarely ever go over 1/2 throttle. I ride usually pretty steadily around 60-70 MPH and at that speed, my throttle position is only about 1/3 of the way. His point was that the high speed jet (Main jet) has very little, if any, influence on mixture. Rarely, if ever, does a person go "full throttle". Most people's riding is done when MOST of the mixture is really done by Needle jet, and jet needle. However, he also pointed out that the idle jet influences virtually all jet ranges as the idle inlet to the venturi is always sending gas to the engine. Hence. he also stated that most people adjust the idle mixture screw too rich (advice I have seen suggested right here on the web site!) and therefore, coupled with needle jet/jet needle being somewhat worn will produce a too rich condition all through the idle to mid-range position.

I am not an expert, by any means, but I went out, and warmed up my bike (took for a 5 to 10 mile ride) and took along a screwdriver. I pulled over, and then set the idle mixture, but this time, I didn't back out screw to "safely" get it richer, I got carbs to their best idle running. This one action affected my engine performance all the way up to 5,000 rpms (about 1/3 to 1/2 throttle position). Ran much smoother and transition from maintaining a constant speed (at virtually any speed) to acceleration was much smoother!

Just my 2 cents
 
Ran much smoother and transition from maintaining a constant speed (at virtually any speed) to acceleration was much smoother!

I think that's called the placebo effect! :stick

Seriously, though, I made note of the throttle while running this morning on the freeway at a steady speed...about 65-70 at 5th gear at 4K RPMs...slightly wind-aided but not much. I was probably at about 1/4 to 1/3 throttle. Probably makes sense because the faster you go, the more the drag goes up (by the square of the speed) and it's going to take more and more throttle to get that next 5 mph.
 
I think that's called the placebo effect! :stick

Seriously, though, I made note of the throttle while running this morning on the freeway at a steady speed...about 65-70 at 5th gear at 4K RPMs...slightly wind-aided but not much. I was probably at about 1/4 to 1/3 throttle. Probably makes sense because the faster you go, the more the drag goes up (by the square of the speed) and it's going to take more and more throttle to get that next 5 mph.

I agree about your assessment about the throttle - has to go up at a greater amount than speed would.

Also, as I was thinking about it, technically, throttle position does not equal speed as per your observation. If one is going uphill (or against wind) at a steady speed (let's say 50 mph) he would have to have greater throttle than if going the exact same speed going downhill (or with the wind at his back). Just an observation that I am sure you already know!!

To be honest, I was skeptical when told. However I tried to be "unbiased" and it really did seem better. My next move when I can get the money together is to purchase new needle jets and jet needles along with appropriate "O"" rings and then diaphragms (although my current ones look good) and gaskets.

As you are aware by now, I am the most unbiased, non-opinionated person you know!! hehehe
 
Even with those variances, as you pointed out, we're running on the "needle" pretty much all the time. According to the Bing book, the main jet doesn't come into play until around 60% of throttle.
 
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