Can't set throttle body sync

PGlaves said:

Somethings are disturbing vacuum as rpm varies. Air leaks are a possibility. Disturbances to induction air flow are also a possibility. The most common is deposits on the heads and stems of intake valves and/or other combustion chamber deposits. Another distinct possibility is small stones or other obstructions to smooth cable wrap down in the grooves of the throttle body pulleys. Check this first.

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deilenberger said:

Frank,

Am I correct in assuming you have done a valve clearance check (as mentioned), and adjustment if needed? If the valves are off - this sort of symptom is often the result.

I would also check that at throttle fully closed you have slack in both TB cables. If you don't - the stepper motors are trying to compensate, and this could also cause what you're seeing.

The GS-911 can be used to lock the steppers - but in my experience - it really isn't necessary. Above about 2,000 RPM the stepper motors seem to be open the same amount (as seen on the GS-911 output), and the openings are relatively small compared to the actual throttle opening. As you open the throttle more - the stepper positions become even less significant.

My experience has been if the valves are correctly adjusted, only once in 95,000+ miles was it necessary to adjust the TB balance, and even that time, it might have been my imagination.

As Paul mentioned, if nothing else works - it might be good to check that the cables are moving in the grooves cleanly and smoothly. BMW added a plastic cover around the grooved sector to prevent stuff getting into it and causing this sort of problem. Unfortunately - the plastic cover makes it harder to check. I've never had anything get caught in the grooves on mine, but that's not to say it couldn't happen. Some people have successfully gotten the plastic cover off without removing the TBs. On mine, on one side I know that's impossible since the plastic cover is right against a frame tube, and TB removal would be necessary. That's not a hard job at all IF you have the correct pliers for removing the bands that hold them into the rubber mount. Doing it without the correct pliers is likely to damage the bands. The pliers can be obtained at any NAPA dealer or Amazon - made by Lisle I believe, and the same bands are commonly used on automotive CV joints. They are small $$ (less then $20 I think..)

If it's your bike that has all the mods listed (it's unclear where the quoted material in your post is from..) - I hesitate to guess - but perhaps something with the mods is causing this behavior.

Good luck and HTH,

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franz said:

Don,

I triple checked the valve clearances when I had the covers off. I know my valves are good. I followed the guidance for the sync in both the JVB DVD and your write-up in the DYI sub forum. I checked and confirmed proper amount of slack in both cables before I completed the sync. I even allowed the twin max to run for a few minutes as you suggested, and the engine was plenty warmed up. I used reducing nipples for the twin max hoses where they connect to the TB teats. I'm reiterating that I followed all guidance literally so that's why I'm perplexed. I wrote Jim Bade a separate email and he doesn't quite know what is going on either, other than to check the items that you and Paul pointed out. I don't want to remove throttle bodies yet. Will recheck the boots to ensure they're tight and buy another new battery for the twin max and try this again on the weekend.

The bike runs great. Idle is smooth and there is absolutely zero hesitation when I roll on the throttle in any gear range. I don't feel a lot of vibration at any given RPM either, but that's just my take. Maybe it's something in the mods I have done to the bike. But I don't have any exhaust leaks and the AF-XIED is balanced per the instruction manual and seems to make the bike run smoother.

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rtwiz said:

Franz:

Are you using a window fan or something in front of the bike when you synch these throttle bodies repeatedly? The bike needs a flow of air to keep temps in range.

Next...Why the heck would you bother with K&Ns on an RT? The filters are not the restriction on these bikes, the air tube is. You put in a higher flow filter and it does...pretty much nothing. Plenty of flow for that tube. For your trouble, you get to clean and expensive filter and risk getting contaminates into the engine as opposed to a nice, high capacity, throw away paper filter. If I'm out on the road in the middle of nowhere? No contest, I want the stock filter. And you run the risk of air leaks if the filters don't seal as well as OEM type filters. I've seen that happen on Porsche filters.

Maybe I'm out of the loop on some of the engine tweaks available for these 2005+ motors. I'm not familiar with what a "flapper" is.

I've had some cars, two BMW M3s, that benefited greatly from K&Ns in conjunction with different intakes and performance software to match. RTs are not in that category. They put the narrow air tubes on there to give a nice, fat torque range, make the bike quiet and great to ride. I go FAST on my '05. It's completely stock. I put a K&N on it once and it really did zero. Maybe yours is different, but I doubt it.

Is the "AF-Xied" you're referring to one of those resister cables for the air filter sensor? Why do you have it? Yes the bike runs richer, but does it run better? All it did on my bike was waste fuel. I took it off. If you're concerned with intake valve deposits, I wouldn't be making the bike run rich.

You have removed your CAT and have a different exhaust, correct? That may make some of these other mods make more sense. If so, ignore me.

Removing a cat really does free up the breathing. Depending on the fuel management on the engine, this can be a very good thing. It sure works nice for bikes with carbs. If it changes things enough to make the bike run lean, then this resister cable might make sense to compensate for that. Still, I think the stock 1200RT hex head engine is pretty great.

Your last paragraph is most telling: "The bike runs great. Idle is smooth. There is absolutely zero hesitation when I roll on the throttle in any gear range. I don't feel a lot of vibration at any given RPM either..."

I'm trying to understand your issue here?

The Twin Max isn't supposed to stay centered at all RPMs. You are measuring average vacuum at the base of the intake tubes. Air is getting pounded back and forth inside there. The speed at which the valves open and close affects that. The speed at which the piston comes down with the intake valve open to pull air fuel in also changes with RPM. I'm not an aerodynamics engineer and haven't studied these tubes specifically but if you look at what's actually going on in there, it shouldn't be a surprise that the vacuum changes a little bit at different RPMs due to these "disturbances to induction airflow".

The intakes are not exactly the same on both sides, so you're getting an average vacuum reading on each side and it seems natural to me that it would wander a bit. Air/fuel hits the intake valves hard when they close and there is a sort of violent reaction to that. As the speed of the air and the speed of closing of the valves changes, the impact does different things inside the intake tubes creating oscillations and such. Paul Glaves described that to you as "disturbances to induction airflow". There are plenty of them and they are not perfectly equal for both sides. Balancing the TBs gets them close for common RPMs used. It's not perfect. If you hold one steady RPM, the reading should stay the same. If not, there's a leak in one side.

If the throttles are moving properly and the valves are adjusted properly and the cables aren't jammed up with debris and there are no vacuum leaks and you're happy with the way the bike runs, my best advice is button it up and enjoy it. Why keep picking at the poor thing? Especially when it takes an hour to remove all the plastic to get to the throttle body adjustment?

If you haven't been putting the very cheapest available regular gas in your bike, I think you can rule out deposits on the head at 6000 miles. The only exceptions to that would be if the bike only runs short trips down to the tavern and back. ...or half of the time has been spent running in the garage while you attempt to find the perfect throttle body synch...or maybe the resistor cable on the air filter is making the mix too rich?

Take the bike out, warm it up for 20 minutes on a normal streets and then flog it. Deposits, there can't be much, will be gone. ...Those would be intake valve deposits. Since these are not direct injection motors, air/fuel flows over these intake valve areas and the detergent in good premium fuel should clean it off as you ride. Regular flogging is like using a toothbrush on these puppies. You have to do it now and then. Most of the people who have troubles are ones who never use the revs and never push. It's a motorcycle!

Newer BMW car engines get intake valve deposits because these engines are direct injection...no fuel goes past the intake valves so no cleaning. After 50K or so, the gunk on the valves starts to do things. They need to be cleaned with ground up walnut shells shot at the valve stems with an air blast. These bikes, so far, are quite different from the car engines although that seems to be changing a little every year. Stay tuned for turbos and lower displacement.

If you're still convinced that something is wrong, PUT THE BIKE BACK TO STOCK and do it all again. If Twin-Max is still wandering, then, hey, I guess it just wanders. With a modded bike, it's hard for any of us to help you with this unless we have the same mods.

Then, if you're still looking for something to do, put one engine mod at a time back on and RIDE THE BIKE 100 MILES to decide whether the mod is actually helpful. Eventually, you'll find the best of them and sell off the rest. Know that there are a lot of useless performance farkels for BMWs out there. Know that these bikes show their best stuff after you've ridden them 100 miles. Often these mods seem cool on short trips but turn out not so cool when you actually go somewhere with the bike...which, to me, is sort of the point.

1200 RTs run awfully well in stock form and really don't need engine mods. Most just make things less robust for the dubious benefit of having a stronger motor at one part of the power curve at the expense of the others and at the expense of economy and/or noise. On an RT, economy counts because economy means range and that means not having to stop for fuel on a long ride or over a long distance between gas stations even if you do stop for photos and leg stretching. These bikes do not lack for power or for torque. They have more than most riders need.

Did you buy an RT because you want to drag race it or because you want to go sport-touring? I bought mine because I wanted something reliable, sweet-running, light enough, comfortable enough, with enough ground clearance and storage to go far away and then be able to carve up tasty roads. Around here (chicago), we get straight, boring roads with a lot of potholes and/or construction, so I have to travel down by you or out west to find the good stuff.

I modded the heck out of my '99 R1100RT. I had good cause. The thing surged like crazy. I did everything I could to stop it. I read all the Bob Lenten articles, took it apart and put it back together with great regularity. I had a "Fuel Nanny" with high and low speed adjustments on it that allowed me to delay the closing of the injectors. The more I delayed, the richer it ran. Then, I changed the jumpers on my bike to the 850cc setting. BMW used a "one size fits all" injection system and there were these jumper plug things in different colors that you could buy to change the fuel curve. I just made my own jumper and followed the instructions that came with the Fuel Nanny. That made it unnaturally lean with the Fuel Nanny set to zero or unplugged. This gave me a blank slate to go from "way too lean" to "way too rich" or anywhere in between with some turns of these little screws on the Nanny. I found a sweet spot but the bike was still a little lean at some RPMs. If I set it richer, I could pull wheelies, but economy went down fast and exhaust started to be sooty. Peak power may have been higher, but it didn't run better...a little worse, in fact. The real fix for these surging motors is dual plugging them. The jugs on these twins are just too big for one plug to get it all done. If all the fuel doesn't burn, you get a false lean that make the bike surge. Complete combustion eliminates the false leanness they had at certain RPMs. To this day I don't think anyone knows why some R11RTs surged and some didn't.

With 1200RTs, there are dual plugs so the burn is complete. The injection is set very precisely by the computer. Servos control the low idle perfectly. The high speed synch stays pretty danged close because the throttle bodies and cable system is SO much better and more stable than the 1100/1150 Bing TB system.

As has been said, "95,000 miles and I've adjusted the synch one time. It was probably unnecessary..."

I had mine done twice. Had a real BMW dealer do it when the bike was new. It ran worse. Shortly after that, I had a non-dealer tech who knows what he's doing do it over and it was good. Now, I just adjust the valves if it starts running a little rough. A careful valve adjustment using 4 feeler gages and the same touch on both sides of the bike solves any rough running and puts the clearances right...and equal.

Know that I have a well equipped garage and in it is a mercury manometer that is well capable of adjusting these throttle bodies. If it ain't broke, I'm not fixing it and I don't care what the readings are.

For longevity of these bikes:

1. Use non-synthetic oil until 20K or so until the rings seat and there is no oil consumption. Then and only then, use synthetic.

2. Warm the bike up completely, not just until the oil temp gage goes to normal, but until all the metal is up to temp. Then don't be afraid to give it the spurs. These motors thrive on it, but not until everything is to temp. This is a very good way to seat the rings after initial break in. My 1200 cylinders are made the same way as the 1100 and 1150 I had. They all use some oil until they are really broken in. If you use synth from the get-go, they won't seat and the bike will use oil forever. This is not true, I've heard, for the new liquid cooled bikes. They use thinner oil and require no break-in.

3. Don't lug the motors. I aim for ~3,000 RPMs for cruising around at lower speeds and choose gears accordingly. When I accelerate hard, it's usually from 3500 or higher.

4. Change the final drive oil every 10K or so. Lube that drive shaft spline while you're in that area every 20K or so. The procedure for changing final drive oil without a bottom plug is outlined in the JVB DVD. It shows how the FD comes apart from the driveshaft. That's where this spline is.

5. I change engine oil every 5K for city riding or 10K for long trips. If you do a lot of cold starts, you need more frequent oil changes.

6. When economy starts to go down for no apparent reason, the air filter needs changing. Stock ones work fine. I have stock exhaust with cat. Could be some small benefit to a low restriction intake if you pull the cat. On a touring bike that runs this good, I'm opposed to dirtying up the air for no good reason, but that's just me.

7. Don't drop the bike or hit anything. Both of those things tend to wear the bike out faster.

Try to have fun.

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beemerphile said:

Finally, the Twinmax is a blunt instrument compared to a Harmonizer. I've spent a lot of time playing with sensitivity of the Twinmax just to get it to quit wagging its tail at low RPM. On my 4-cyl. K I use a Morgan Carbtune. The Twinmax is a pegboard ornament of a bygone era.

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keepitsim@gmail.com said:

While using the GS-911 I’m can not get a steady vacuum reading at ant rpm setting. I’m using the Hyans service book and followed the directions the 911 stated. All cables and valves are within the specs. I put my thumb over the vac tube and feel some blow back. Any suggestions?

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