* My question: which way should I turn the screw( in or out ) to uncrease the fuel mixture? Counter clockwise. Someone correct me if wrong, but the fuel mixture screw is only for idle up to 1/4 throttle. I don't have my bing book in front of me but I think your initial setting before warmup and sync is 1/2 turn out from full set.
* I want to add more fuel to the mix but I'm not sure which way I should be turning the screw. Counter clock wise. Small increments.
* I checked MaxBMW's parts Fiche and they only show (1) available jet for my carbs. Are there more? Yes, you can increase/decrease. I'm sure Max is giving you stock, which is correct unless you've messed with your airbox/exhaust/etc.
* And how hard is it to replace the the jets with richer jets if I can find them? Simple. Pull off float bowl and it is right there in the center. It will take you WAY longer to get the carb off and on. Unless you want to do it on your back or on a lift. Might take 12-20 seconds to change it. Don't forget the washer that is on there.

Try the initial settings for your carb. Set the mixture screw and then set the idle screw to a point to where is just grabs a sheet of paper then 1 full turn out. It should run pretty well to go for a ride to start your sync.

There are a million sites about syncing, so I won't get into it here.

* I have a 1980 BMW R100T bike.
1. My question: which way should I turn the screw( in or out ) to uncrease the fuel mixture?
2. I want to add more fuel to the mix but I'm not sure which way I should be turning the screw.
3. I checked MaxBMW's parts Fiche and they only show (1) available jet for my carbs. Are there more?
4. And how hard is it to replace the the jets with richer jets if I can find them?

1. Neither way will enrichen the mixture. Here I assume you're talking about the mixtures at road speeds, because no one cares about mixtures at idle. And the reason for this is that the idle passages, which have the only adjustable mixture screw on a Bing, contribute such an infinitesimal portion of the total mixture at road speed that it cannot affect the road speed mixture. In effect you're turning a screw that affects 1%, hoping to influence the other 99%. Ain't gonna happen.

2. Answered in No.1

3. Yes. You simply need to look on other fiche at Bing carbs for other models.

4. No it is not hard. You do need to shut off the fuel and remove the float bowl. The 2 jets you care about are the Needle and Main. Both are removed with a single swing of the wrench. The numbers tell the story. The larger the numbers, the more fuel they flow.

That subject being settled, let me add this....
• Color Tunes are a great asset, if you know how to interpret them properly. Color Tunes also harken to an age before ethanol fuels and several other major changes in fuel, carbs and engines. So the bottom line is NOT the color of combustion, but a simple "does the bike perform correctly" ?

• Adjustment of the carbs is unlike other aspects of tuning in that there is VERY FEW static settings you can check with a gauge. Most important adjustments are made dynamically, and these settings are a direct result of subtle changes in spark, compression, timing, and 100 other aspects of tuning. Thus all carb adjustments are made when ALL other aspects of tuning are perfect. So the questions need to be asked... Is the compression good? Is the compression matched on both cylinders ? Are the sparkplugs new ? Are the spark plugs correct ? Are the plug wires new ? Are the plug caps new ? Is the fuel high octane and less than 4 weeks old ? Are the valve adjustments correct ? Has the ignition timing been set with a strobe at Full Advance ? Have both intake hoses been replaced ? Are the blocking screws for the carb balancing holes in place ? Is the air filter new ?

I say this because if you don't understand your question #1, then you most probably didn't know the rest of this. That means your issue is most likely not carburetion at all !! I'm not saying your carbs are perfect, but if Bing just rebuilt them, then I highly doubt they are far enough out of adjustment to run poorly. Just saying.

All the best.

That R100T is a fine motorcycle. With it's high compression it makes about 5 extra hp. You didn't say anything about syncing the carbs (and cables) but I'm sure you must have. Even with everything else being up to par, that sync. can make a world of difference in running rough. Wouldn't hurt to double check that. Good luck.

Let me ask it simply, what does changing the fuel/air mixture screw do?

1) If I screw it in, does that change?
2) If I screw it out, what does that change?
3) Does it only have an effect at idle?

Thanks...

1. Screwing it in (clockwise) makes the idle mixture leaner.
2. Screwing it out (counterclockwise) makes the idle mixture richer.
3. According to the Bing Book "the idle circuit contributes fuel until approximately half throttle". I personally am not sure exactly how much the idle circuit contributes to throttle at road speeds, i.e. what is "half throttle" in rpm?

1. There are "idle mixture screws" and there are "pilot" screws. The previous definitely changes the mixture, typically regulating only the fuel portion of the mixture. Therefore "out" equals "richer". In the case of the latter, which I believe the Bing uses, the mixture is fixed, what the screw does is vary the volume of mixture. That's 2 different beasts.

2. There is no shut-off valve for the idle mixture passage within the carb. If there is, then please show it to me. Instead, fuel will ALWAYS flow from atmospheric pressure (as found inside the float bowl) to low pressure (as found inside the carbs venturi). ALWAYS. This is the basis for all carburetor functions. So right there we settled the issue: If the engine is running, then fuel is ALWAYS flowing through the idle circuit.

So it is not that the idle circuit turns off, because it doesn't need to. Instead, it simply becomes such a small contributor to the total fuel entering the engine at road speeds (3000 RPM), that it is inconsequential to the total, and therefore meaningless. That's what the Bing manual is trying to say. That's what I'm trying to say. Adjusting the idle circuit screw and looking for mixture differences on the plugs at road speeds is a total waste of time.

Apologies for being so blunt, but this is the exact question you asked several days ago and again the exact information I gave you several days ago. And yet you persist in asking the same question.

All the best.

Thanks for your reply. I had to read yours and everyone else's reply about (5) times to figure out what's exactly going on with my bike.

So, I deduced the following.
* The fuel/air mixture screw only has an effect at idle. Who would have guessed?
* Turning the fuel/air mixture screw CCW(out), makes the 'idle' mixture richer.
* Turning the fuel/air mixture screw CW(in), make the 'idle' mixture leaner.

So to answer some of your other questions:
* I'm using fresh 91 octane gas.
* I'm using new BMW W5DC spark plugs. Some places I read say I should use W6's and other places say W7's as well. Not sure what's correct.
* Brand new NGK spark plug wires.
* I sync-ed the carbs using a CarbTune Pro vacuum gage. Funny though, when I first hooked it up, one side was up about 1/3 of the way. The other side was up about 2/3 of the way. So I brought the higher side down to the lower. My brother said I should have gone the other way, brought the lower side up to the higher side's level. Any ideas there?
* My Compression is not all that great, L=128, R-134.
* Haven't checked the valves.
* Set the timing about (3) years ago before I tore the bike down for restoration. It's just been sitting since. I believe I set the time at idle, not full advance. I see the Rider's Manual states set it at 3500 RPMs. So that needs to be checked.

Another question:
* I have the original blue Rider's Manual from BMW. It states about fuel on-page 84, and I quote, "leaded or unleaded, min. RON = 91"

This is a 1980 R100, is it true it can run on leaded, or unleaded fuel?

Thanks for all the replies!!!

The R 100T is a high compression engine. It needs premium fuel. It will run on unleaded fuel.

So to answer some of your other questions:
* I'm using fresh 91 octane gas.
* I have the original blue Rider's Manual from BMW. It states about fuel on-page 84, and I quote, "leaded or unleaded, min. RON = 91." This is a 1980 R100, is it true it can run on leaded, or unleaded fuel?

Research Octane No (RON) is what they use in Germany. In the USA we typically use the average of the Research & Motor methods (R+M/2). You should be running the highest octane available from a name brand, Top Tier fuel provider. That should get you an octane of about 92 or 93. (Read this: https://toptiergas.com/ )

All these engines can run on leaded or lead-free. The only difference is that earlier models will experience accelerated valve seat wear. Most riders of under 100,000 miles don't need to worry about calamity, they only need to adjust their valve clearances more often.

* I'm using new BMW W5DC spark plugs. Some places I read say I should use W6's and other places say W7's as well. Not sure what's correct.

So you're trying to read a plug, but you're not sure if it's the correct heat range to begin with ? Go get a set of NGK BP7ES plugs, lube the threads, and install those. Stop all the guessing.

* Brand new NGK spark plug wires.

You need Metal-Core plug wires. In other words, spark plug wire with traditional copper or steel conductors in the center. I don't think NGK makes a metal-core wire because most cars since 1970 have run suppressor type wires.

* My Compression is not all that great, L=128, R-134.

That's normal compression.

* Set the timing about (3) years ago before I tore the bike down for restoration. It's just been sitting since. I believe I set the time at idle, not full advance. I see the Rider's Manual states set it at 3500 RPMs. So that needs to be checked.

And that's my concern. This thread has carried on for 2 pages with a fixation on a screw direction. This while the reality is that the basic, most fundamental tuning steps have not been attended to. Fix the plugs and plug wires, set the ignition timing correctly, and start running good fuel and you'll get the results you want.

And to answer your screw direction question. The idle mixture is set by engine RPM. You adjust the screw for highest RPM, because that means it's the most efficient mixture. Efficiency is what you want at idle, not a pre-determined mixture or plug color.