Bing Baselines.....

[BubbaZanetti]

After replacing my floats a few weeks back i noticed that the bike was taking forever to warm up and not run poorly. Once warm, it runs fine and smooth. Someone had suggested that it was running too lean at idle and that was the only reason it was running poorly cold. I got out the twinmax, warmed the bike up and adjusted the idle mixture screws out a bit, which slowed the rpms at idle (a good thing as i was idling at about 1300-1400 rpm, a bit high). Today was my first ride since then and it's still running very poorly cold.

what are some good baselines to use in regards to number of turns out for the screws, etc. i've also come to notice that my throttle cables are quite "slack" they seem to have a bunch of free play at idle, doubt this has any effect.

[Bill Burke]

A very generic approach: MIXTURE SCREW all the way in to a gentle seat closed, then back it out 3/4 turn. IDLE SPEED SCREW: Back it all the way out, then (using a feeler guage or other clever approach), turn it in until it just makes contact with the butterfly lever, then one full rotation in (clockwise).

[20774]

The Bing manual shows for R80ST carb #351/352:

- idle mix setting -- 0.5 turn out
- main jet -- 135
- needle jet -- 2.66
- idle jet -- 45
- needle clip position -- 3

Provided the cables have been synched, excessive slack in the cables results in a delay in carb actuation. You have to turn the grip that much extra just to get rid of this slack so that the cables will begin to operate the butterfly. You really want the minimum slack necessary so that when the bike is at idle, there will always be some slack regardless of the temperature. That way you have as little slack to "eliminate" as you twist the grip.

[Bill Burke]

Along with too much slack in the throttle cables you can have too little. Good is about 2 or 3 mm slack in each. One way to test for too little: idle the engine and turn the handlebars stop to stop, left and right. If the idle speed changes, you've got too little slack.

[FrankT]

I've been through more than a few re-builds over the decades so maybe I can reply. Assuming all your internals are ok, you have no vacuum leaks, your cable slack is ok, and your idle mix is set to the precribed intial setting, I would first check the gas level in the float bowls. I assume your R 80 has 32mm Bings. A trusted mechanic told me decades ago not to adust the float level based on the method stated in the Bing Manual but rather use a measurement based on gasoline depth. For the 32mm Bings, this should be 16-18mm as measured from the circular depression in the float bowl to the gas level. I use the depth gage on my Vernier to measure this. After that, set the idle screws such that they only make initial contact with the adjuster lever on the carb. Take your bike for a ride for several miles so that it is fully warmed up. Adjust the idle rpm/speed and throttle cables accordingly as usual. I have use this for more years than I can remember and my R75/5 idles like a Swiss watch.

[sumran]

There are large differences is the starting point on the idle screws, depending on the model of airhead. Kurt's post is very helpful since it gives the setting for your model. I agree with what he said about cable slack. You don't want to give away the first part of the throttle action to slack.

I do not use the twinmax when setting idle mixture, although I do use it to set the final idle and sync. IMO, there are too many variables that affect vacuum balance and the idle mix needs to be set one side at a time. I want it nailed down before I get to the other settings.

For the initial settings and idle mix I use grounding sticks (easily made with a piece of spoke or a bolt attached to the spark plug ferrel that gets thrown away with our bikes). I start at the factory settings with a well warmed engine. Air blowing on the engine and all that good stuff. Check for reasonably well balanced idle at 1,000 RPM's. I check this by grounding one side then the other. The engine should drop down to the same RPM on each side when the other is grounded out.

I ground one side. The engine will idle at about 550 rpms, just enough to keep running. I then turn the mixture screw in (leaner) a 1/16th turn at a time until the engine stats to bog down. I back off the screw (richer) 1/8th turn from that point, and the do the same adjustment on the other side. Bing recommends a slower process that involves riding the bike and leaning the mixture 1/8th turn at a time until it bogs off idle, then backing it out an 1/8th. That requires more patience and lots of mounting and dismounting.

Once I set the idle mixture this way, I use the twinmax to adjust the idle mixture and sync, paying careful attention to the amount of cable slack throughout the process.

I expect there are many other methods to get the job done, but this one works well for me.

[BubbaZanetti]

I've been through more than a few re-builds over the decades so maybe I can reply. Assuming all your internals are ok, you have no vacuum leaks, your cable slack is ok, and your idle mix is set to the precribed intial setting, I would first check the gas level in the float bowls. I assume your R 80 has 32mm Bings. A trusted mechanic told me decades ago not to adust the float level based on the method stated in the Bing Manual but rather use a measurement based on gasoline depth. For the 32mm Bings, this should be 16-18mm as measured from the circular depression in the float bowl to the gas level. I use the depth gage on my Vernier to measure this. After that, set the idle screws such that they only make initial contact with the adjuster lever on the carb. Take your bike for a ride for several miles so that it is fully warmed up. Adjust the idle rpm/speed and throttle cables accordingly as usual. I have use this for more years than I can remember and my R75/5 idles like a Swiss watch.

interesting, snowbum has it a good 1/3 higher:

For the 32 mm carburetors, use 24 mm fuel height.


i plan on going into these a bit tomorrow. to me, it seemed as though the bike ran better (and warmed up faster) before i twisted the idle mixture screws out a bit. maybe i will turn them back in a ways, then bring down the idle more with the throttle stop screws. someone mentioned "bog" as you turn the screws in, mine seems to do the opposite, which, imo is how it should be, more fuel (screw out - lower rpm) lean out the mixture by turning the screw in and the rpms go up.

again, bike seems fine (although if i let someone who knows these things ride it, they might say other wise) once it's warmed up and anywhere from "off idle".......go figure.

[DennisDarrow]

It would seem as if you have your air screw out TOO far if when you screw it in the idle picks up a bit. Depending upon how much your idle screw is set in, the air screw may have as little as 1/4 turn actual adjustability. This is often hard to catch as you bring the screw out from the fully screwed in position.

Randy has a good method there. Have the engine idling at an acceptable level. RIDE IT FOR A FEW MILES FIRST RATHER THAN WARMING IT UP BY SITTING.......Then unplug one cylinder, grounding it of course, THEN, screw the air screw IN all the way until it dies, or listen carefully for it to almost die as you go in almost all the way. NOW, back it out carefully, and when it runs the best, often just a 1/16th of a turn, go barely back in.

This should get you really in the ball park, now go down with the idle screw a bit, readjust the air screw accordingly and do the other side. NOW sync the cabkes. For me, I like to end up with an idle that the red alt/gen light is barely coming on/going off. For some a bit slow RPM; but sounds great as folks think when is that thing going to die, and never does. CHUG CHUG CHUG

Again though, it seems your air screw is OUT past the adjustability point when you begin to adjust if your idle picks up as you go in.............Just thoughts.......Good luck.........Dennis

[sumran]

There are many approaches to the idle mixture adjustment. Some of the guys I ride with turn it in until it slows down, then turn it out until it slows down, then leave the screw between those two points. That is usually close to the factory setting.

Some adjust theirs like Derek because they feel they would rather be rich than lean and they are not very concerned about mileage. They are more concerned about possible damage if the mixture is lean.

The Bing book method of adjustment instructs you to keep leaning it out until performance suffers, then make it one notch richer to restore performance. The manual says that anything more than that wastes fuel and provides no benefit. That is what I am shooting for when I adjust them.

I certainly don't think my way is right and the others are wrong. I don't think the book is the final word on how someone should adjust their carbs. It is partially determined by how you ride, how much you ride and how often you clean and adjust the carbs. If they are tuned for max efficency, it doesn't take much crud to throw them off. But you will get better mileage, good performance and cleaner internals.

[vanzen]

Bear in mind that preliminary settings listed in the manual for the idle mix
are just that – preliminary settings.

i.e. the correct needle position with which to begin tuning.

Best needle position will vary relative to gas quality, altitude, phases of the moon, and etc.

Certainly, one can suspect trouble if:
left and right settings vary from each other significantly,
both settings are significantly different than the preliminary, or
adjusting the needle(s) does not affect rpm / engine speed.

I use BMWs method (turn it in until it slows down, then turn it out until it slows down, then leave the screw between those two points) and a manometer.
A little "fine tuning" may be in order after a road test.

[BubbaZanetti]

The Bing book method of adjustment instructs you to keep leaning it out until performance suffers, then make it one notch richer to restore performance. The manual says that anything more than that wastes fuel and provides no benefit. That is what I am shooting for when I adjust them.


this idea sounds good to me, i'm certainly not concerned about leaning things out a bit. if the bike ran kinda crappy before and now is running crappier at a richer setting, then i prob need to lean it out a bit. i guess i didn't realize (or have never turned them in that much) that it begins to stumble at some point, but it totally makes sense, since the bike is getting little to no gas at that point.

i think i'll go to the garage after work, ride it around for 10 or 15 min then turn the idle screws in till the bike stumbles, turn them out a tad and get an equal "sound" (a bit harder to do with my 2 into 1 pipe), then adjust for desired rpm using the throttle stops.

it does feel like its an "overly rich poor running" issue though.

[sumran]

... phases of the moon...

:laugh

Do the new models have a POM sensor to adjust for this variable?

[Guenther]

The main carburetor has a much higher airflow than the idle bypass. So, once the throttle is opened a bit the setting of the idle air mixture (it controlls the amount of gasoline added to the idle bypass) very quickly does not contribute to the mixture leaving the carburetor.

If the has problems running smooth when cold then it is the "choke" part of the carburetor not doing its thing. Actually this type of Bing doesn't "choke" the engine but rather adds more gasoline straight into the air stream. I was told that the gasket under choke housing can leak and give you poor cold engine performance.

Whenever "cold/warm engine performance" comes up my mind goes "valve clearance". Have you checked that?

/Guenther

[BubbaZanetti]

The main carburetor has a much higher airflow than the idle bypass. So, once the throttle is opened a bit the setting of the idle air mixture (it controlls the amount of gasoline added to the idle bypass) very quickly does not contribute to the mixture leaving the carburetor.

If the has problems running smooth when cold then it is the "choke" part of the carburetor not doing its thing. Actually this type of Bing doesn't "choke" the engine but rather adds more gasoline straight into the air stream. I was told that the gasket under choke housing can leak and give you poor cold engine performance.

Whenever "cold/warm engine performance" comes up my mind goes "valve clearance". Have you checked that?

/Guenther


fairly recently (less than 2K ago). the bike started running poorly at a cold idle after 2 things. 1 - going to a slightly colder spark plug (for hot riding in the city) and 2 - fiddling with the carbs.

[vanzen]

:laugh

Do the new models have a POM sensor to adjust for this variable?

YES ! and fortunate it is, too !
... removing that task from the lunacy of POs discretion.

[mmmalmberg]

Also if this is not obvious, make sure everything else is in order before trying to dial in your carbs. Valves should be spot-on, likewise with timing, plug condition, air filter, make sure there's no leaks in the intake path... These can all affect carburation.

[BubbaZanetti]

took the bike out and warmed it up today. did the comprehensive balancing per snowbum's recommendations . fuel level was perfect according to his specs for the 32mm bing (24mm of fuel give or take a mm). fuel turned on and off when floats were raised/lowered at exactly the spot prescribed (top of float level with carb housing bottom). valve adjustment is very recent, no known intake track leaks, air filter is new within the last 2K miles. pulse air system recently plugged to spec. spark plugs pulled today revealed a nice (although mabye slightly dark) tan, certainly not white or black.


after warm up, balanced the idle by doing the following:

1 twist out from light seat on the idle circuit. worked my way in from there to highest rpm, then to stumble, then backed them out again (i would guess 1/8 or so tun) to highest rpm. backed off throttle stop screws till idle was perfectly balanced at about 1000-1100 rpm, noticed the left screw seemed a bit more "in" than the right, just a tad. took up all the slack in the throttle cables @ the carbs till i achieved the recommended freeplay, handlebar turning reflected there was enough, no change in idle speed. brought the idle up to between 1500 and 2000 rpm and balanced there, using the right cable adjuster. readings were somewhat "all over the place" but i found where it pulled hard left on the twin max, where it pulled hard right and set it in between the two, achieving a relatively stable balance.

rode home and the bike seemed "ok". not sewing machine smooth, but it didn't stall or do anything weird like it had been. leaving VERY early tomorrow (long before the sun comes up) for a YB rally up in MA, we'll see how it does. i guess these bikes can just be a bit finiky. does the above method sound "ok" to you guys???

[sumran]

A couple of things that make a big difference for me.

I can't get the idle mix right unless I isolate each cylinder.

When adjusting the throttle cables for sync, I want to add slack cable rather than removing it. If I get balance by tightening a cable it gets involved in the idle and throws off the idle settings I just finished.

The twinmax will bounce if the sensitivity is too high. I back that off until the needle is stable. Then the adjustments are easier. At least if I can remember that slowing the engine down makes the vacuum go up.

[20774]

When adjusting the throttle cables for sync, I want to add slack cable rather than removing it. If I get balance by tightening a cable it gets involved in the idle and throws off the idle settings I just finished.

Randy has a good point. The trick to always slacken the cable when trying to find the synch point. Consider what might happen if you were to remove the slack in the cable too much, you could remove all of the original slack (~2mm) you had in the cable at idle. What will happen is you'll get a nice cable synch under tension, but when you go back to idle, you won't be synched at idle because one throttle will be under a slight amount of tension now. You want no tension at idle...the ~2mm of slack (depending on final settings and heating of the cables) should still be there when done.

[carockwell]

Years as a smog check mechanic - warning! smog check mechanics don't work on bikes! (yet) -I have had to set the idle for optimum running on thousands of old fashioned British and European cars. Once the idle synchronization is set, you simply twist the idle mixture screw for maximum rpm. If your maximum rpm is too high or too low, then you need to adjust the idle speed screws again, resynch the carbs, and readjust the idle mixture screws.
This works perfectly on my R 80 ST. I can understand that people get twisted around in this process. You can purchase a Colortune spark plug to help you. With a Colortune, the instructions are wrong. You want to adjust the flame color from blue (lean) until the the flame just turns completely yellow. Do this for both carbs, and you will be very close to optimum. Now you just make a minor adjustment to the mixture screws to get the maximum idle speed.

When setting old fashioned multiple carbureted cars for optimum idle using a four gas analyzer, you tune the car to get the oxygen level to zero, this means you are getting complete combustion. On multiple carbureted cars, the optimum idle mixture is usually an air/fuel ratio of about 12.5 to one and a CO level of 6%. This also seems to work fine on my R 80 ST. It is possible to get smog check guys to measure your exhaust at idle, if you promise they don't have to do anything else while you adjust your idle. There is no real benefit to doing this as the "adjust idle mixture for maximum speed" is very close to the optimum mixture. Further tweaking just reduces the emissions some.