Throttle Body Sync?

JK · Feb 19, 2008

FWIW -

Have nearly 16,000 miles on my R-12s since buying it in May, of last year. My question involves throttle body sync adjustments and out of adjustments.

Specifically, done all the Dealer Mx/Svc. Here's my feedback on sync/valve adjustments:

o Out of the box, in Denver, the bike was "buzzy."

o Next day, changed oil at 200 mile, sync adjusted and most of the "buzz" went away.

o The 600 mile service sync/valve adjustment, in SLC, brought back a mild buzz.

o The 6,000 mile sync/valve adjustment, in CLE, made the bike ride "baby butt" smooth. Stayed that way until the 12K service.

o The 12,000 mile sync/valve, in Den, brought back a mild buzz that continued to get worse.

o Got my second set of M-3s (have gone through three sets total, original set was M-1s) at 16,000 miles. Mentioned buzz. They re-synced throttles and now it's gone back to being baby smooth.

In summary, from 6K to 12K the bike ran like glass and the sync never varied. However, from 12K to 16K it seemed out of sync and distinctly got worse.

In conclusion, what causes the throttle sync to remain stable? And what causes it to wander. :bolt

Any insight from our resident motor-heads???

With interest and appreciation....

J.K. :wow

gulfcoastbeemer · Feb 20, 2008

After letting my BMW dealer perform all valve and throttle-body adjustments with mixed results, I performed my own valve adjustment and throttle-body sync at 21,000 miles on my '07 R1200RT. The results were a dramatically smoother engine. I could immediately feel the difference as well as see it in the mirrors

Before I performed the throttle-body sync, I adjusted the valves with the engine stone cold. I used a Twinmax throttle-body balancing device.

And, for what its worth, I didn't disconnect the "stepper motors" during the TB sync, and I optimized the sync at about 3,750 RPM, where the engine spends a lot of time.

I'm pretty methodical and slow as molasses in January when I work on my bike. I'm not sure all professional mechanics or shops have this luxury. That could be the reason some tune-ups are better than others.

deilenberger · Feb 20, 2008

WAG:

I suspect the most critical adjustment on the hexhead engine is valve adjustment, and it's possible the valves drifted a bit and finally settled in between the 12k-16k interval where things were buzzy.

It would seem that once the throttle cables stretch-in, they should stay pretty stable until they start to fail. When I've adjusted my valves and then checked sync with a Twin-Max, the sync has been dead-nutz on. The steppers are primarily for idle balance and idle speed, and are probably a very insignificant factor above idle (small-hole vs large hole when the throttle plate starts opening..)

JK · Feb 20, 2008

gulfcoastbeemer said:
After letting my BMW dealer perform all valve and throttle-body adjustments with mixed results, I performed my own valve adjustment and throttle-body sync at 21,000 miles on my '07 R1200RT. The results were a dramatically smoother engine. I could immediately feel the difference as well as see it in the mirrors

Before I performed the throttle-body sync, I adjusted the valves with the engine stone cold. I used a Twinmax throttle-body balancing device.

And, for what its worth, I didn't disconnect the "stepper motors" during the TB sync, and I optimized the sync at about 3,750 RPM, where the engine spends a lot of time.

I'm pretty methodical and slow as molasses in January when I work on my bike. I'm not sure all professional mechanics or shops have this luxury. That could be the reason some tune-ups are better than others.

Thanks guys -

Stone cold engine may be the secret. Woody, at BMW of Cleveland, spent a full 30minutes dickering with the valves, then sync, to dial her in. Know when I do my other R90S and /6, a few judicious hits with the mallet on the cam bolt removes any double images of the timing marks, and really smoothes out engine vibrations. So much for the virtue of points and plugs.

Also, since I tend to keep the RPMs between 4,000 - 4,500, some tune-ups may keep my humping hamsters happier than others.

Anyway, the new ride keeps me "slow" happy. The only thing that gets tired is changing the tires.

Thanks, again.

J.K. :wow

bob1100rtc · Feb 20, 2008

My 07 RT was pretty smooth on delivery. The only thing I noticed was an occcasional stall on a hot restart. After the 600 mile service (done at 850) there is definately more vibration,an occasional pop when I blip the throttle to down shift , and it stalls more frequently on a hot or cold start. I'm at 2,750 miles now. Before I bring the bike out of hibernation, I intend on rechecking the valves and tb's. I'm also going to change the oil in the engine,trans and fd. That way I know whats in there. I had the dealer do the 600 mile only for warranty purposes. It was torture to let someone else work on a vehicle of mine.

JK · Feb 20, 2008

Bob1100RTC said:
My 07 RT was pretty smooth on delivery. The only thing I noticed was an occcasional stall on a hot restart. After the 600 mile service (done at 850) there is definately more vibration,an occasional pop when I blip the throttle to down shift , and it stalls more frequently on a hot or cold start. I'm at 2,750 miles now. Before I bring the bike out of hibernation, I intend on rechecking the valves and tb's. I'm also going to change the oil in the engine,trans and fd. That way I know whats in there. I had the dealer do the 600 mile only for warranty purposes. It was torture to let someone else work on a vehicle of mine.

Hey Bob -

Don't think the valves alter the sync that much. By only adjusting the throttle body this week, the bike went back to riding as smooth as glass.

Consequently, that's why I asked the question.

J.K. :wow

P.S. It was out of whack by three bars, per mechanic at Foothill's BMW.

apopj · Feb 20, 2008

Sync'd at 3750??

Hello all,

Just a quick question..... Shouldn't the throttle bodies be in "sync" at all rpms? Why would they "sync" at one setting and not all the others? The cables done stretch at certain rpms and not others, so why the "sync'd at" thingies????? Not sure if it matters, but really would like to know.....

Thanks, Jeff

deilenberger · Feb 21, 2008

apopj said:
Hello all,

Just a quick question..... Shouldn't the throttle bodies be in "sync" at all rpms? Why would they "sync" at one setting and not all the others? The cables done stretch at certain rpms and not others, so why the "sync'd at" thingies????? Not sure if it matters, but really would like to know.....

Thanks, Jeff

They should be in "sync" at all RPMs - except perhaps right off idle (since the stepper motor idle adjusters can effect the reading just as the throttle-plates are cracked open.)

On earlier twins - especially airheads - it could be difficult to get really matched throttles over a wide range of opening due to how the cables are seated in the Bing carbs. The cables were typically slightly angled going into the adjusting ferrule, and as you opened the throttle - they tended to straighten up a bit. The change in angle could result in very slightly off carb sync on an airhead, so the hot setup was to tune for the RPM you usually ran at. That said - I usually could get those close enough that it didn't matter..

That doesn't seem to be the case with Hexheads. The cable runs are short, the junction box seems to be good, and I have no problem getting good sync over any RPM range I'm likely to use.

One note - the adjustment is MOST sensitive at lower RPM's - since the difference in opening remains the same, but at smaller openings - it's a larger percentage of the actual opening (dunno if that makes sense - but it's the best I can do..) I like to check the sync at around 2,000-2,300 RPM. If it's right there - chances are excellent it will be right at higher RPMs unless something is significantly wrong.

One other note - the valve adjustment makes a BIG difference in how good the sync is. Valves should always be checked before checking sync. Failing to do this means you're possibly compensating for a misadjusted valve by adjusting the TB sync. You end up chasing your tail that way..

JK · Feb 21, 2008

deilenberger said:
They should be in "sync" at all RPMs - except perhaps right off idle (since the stepper motor idle adjusters can effect the reading just as the throttle-plates are cracked open.)

On earlier twins - especially airheads - it could be difficult to get really matched throttles over a wide range of opening due to how the cables are seated in the Bing carbs. The cables were typically slightly angled going into the adjusting ferrule, and as you opened the throttle - they tended to straighten up a bit. The change in angle could result in very slightly off carb sync on an airhead, so the hot setup was to tune for the RPM you usually ran at. That said - I usually could get those close enough that it didn't matter..

That doesn't seem to be the case with Hexheads. The cable runs are short, the junction box seems to be good, and I have no problem getting good sync over any RPM range I'm likely to use.

One note - the adjustment is MOST sensitive at lower RPM's - since the difference in opening remains the same, but at smaller openings - it's a larger percentage of the actual opening (dunno if that makes sense - but it's the best I can do..) I like to check the sync at around 2,000-2,300 RPM. If it's right there - chances are excellent it will be right at higher RPMs unless something is significantly wrong.

One other note - the valve adjustment makes a BIG difference in how good the sync is. Valves should always be checked before checking sync. Failing to do this means you're possibly compensating for a misadjusted valve by adjusting the TB sync. You end up chasing your tail that way..

Hi Don -

On my R-90S and /6, I run Dell'Orto and Mukuni carbs, respectively. To adjust the cables for equal slack, I use the "sound" of the slide slapping the bottom of the carb to make sure that things are in "sync."

Regarding valve settings, after the engine's properly broken-in, they shouldn't be "wandering." If a simple TB adjustment kills the "buzz" throughout the engine's RPM range, then I'm a happy camper. Following the KISS principle, it's best to keep the variables down to a minimum.

In short, if it works, don't fix it....

J.K. :wow

P.S. And chasing tail isn't always a bad thing, unless you're a trout. :lurk

bikerfish1100 · Feb 21, 2008

JK said:
Regarding valve settings, after the engine's properly broken-in, they shouldn't be "wandering."

care to explain that statement? the only valves i've ever known to not require adjustment during their life are those that are hydraulically actuated, i.e.; self-adjusting.

JK · Feb 21, 2008

bikerfish1100 said:
care to explain that statement? the only valves i've ever known to not require adjustment during their life are those that are hydraulically actuated.

Sure -

Once the valves are properly seated and adjusted, they tend to wear in unision. Adjustments tend to be incremental, and unless not properly tourqued down, one valve shouldn't wildly go out of adjustment versus the others.

Other factors that may enter and alter the equation are improper cooling and lubrication of one cylinder over another, or manufacturing defects and tolerances.

That's why you check the clearances and inspect the oil.

Although I have 200K+ exerience on R-90s, Hex-heads may be different. That's why I ask...

J.K. :wow

bikerfish1100 · Feb 21, 2008

well, that idea of "ideal" equal wear between the sides could expalin why one side might not vary much from the other, but they still require adjustment to bring them back to spec. maybe your thoughts about the meaning of "wander" was different than mine?

JK · Feb 21, 2008

bikerfish1100 said:
well, that idea of "ideal" equal wear between the sides could expalin why one side might not vary much from the other, but they still require adjustment to bring them back to spec. maybe your thoughts about the meaning of "wander" was different than mine?

Hi BF1100 -

The crux of my question addresses and involves the issue of engine vibration. When everything's well and swell, the bike runs good as gold and smooth as silk.

Then it goes in for scheduled service and comes out "buzzy." The two variables being adjusted are 1) the valves, and 2) the throttle body sync.

Take it back to another shop for new tires, mention the "buzz," only the TB sync gets readjusted and bike immediately goes back to smooth running.

Clearly, proper valve adjustment, operation within specs, is extremely important.

What bugs me, however, is how the TB sync can be smooth for 6K, get serviced, then goes from buzzy to worse in less than 2K. Re-adjust, now good as gold.

Hope this post better paints the picture/question in HD.

J.K. :wow

P.S. My R-12S is a daily driver (20 - 150 miles), not an art ornament/ museum piece.

cwsenn · Feb 21, 2008

JK said:
What bugs me, however, is how the TB sync can be smooth for 6K, get serviced, then goes from buzzy to worse in less than 2K. Re-adjust, now good as gold.

Hope this post better paints the picture/question in HD.

J.K.

I do my own syncs and valve adjustments, etc... I am thinking a possibility to consider is that once your bike was serviced the mechanic may have failed to tighten the nut holding the cable adjustment in sync, after some time the cable adjustment changed and then once re-syncronyed good as gold.
With this thought it would make sense that you might want to consider servicing your own bike. No shop mechanic is going to be as careful as you are to get the perfect valve adjustment or sync on your own bike.

Chuck

JK · Feb 22, 2008

cwsenn said:
I do my own syncs and valve adjustments, etc... I am thinking a possibility to consider is that once your bike was serviced the mechanic may have failed to tighten the nut holding the cable adjustment in sync, after some time the cable adjustment changed and then once re-syncronyed good as gold.
With this thought it would make sense that you might want to consider servicing your own bike. No shop mechanic is going to be as careful as you are to get the perfect valve adjustment or sync on your own bike.

Chuck

Thanks Chuck -

Makes perfect sense.

J.K. :wow

P.S. Looks like it's time to buy the hex-head service video CD, and to get busy.

Polarbear · Feb 23, 2008

BMW Dealers mechanics;

Are somewhat skeptical of throttle bodies adjusting procedures and don't like the process, I've heard from many(BMW Mechs)! The BMW computer check they hook up has tolerances for the bodies and if close, they are left alone, untouched. My BMW Master Tech, has little regard for adjusting the bodies in perfect order, because it is not possible, without much hassle and doing it over and over, until you hit it dead on. The high tech aides are helpful, but the bodies are so sensitive to change, the cables can only do so much and are easily suspect. You do your own and get it right and this is great. Do not expect any BMW mechanic to do any better, is where I come from. Its been told "so many times", the bikes come from shops running more poorly than when they went in. Its a very old story here. I know my new GSA1200 has smooth spots and buzzy spots, in the rpm ranges, so go figure how to get rid of this! It is not perfect, but not far off, so I run happy for now. Randy13233. PS; my cam chain seems noisy at certain engine rpm's, too. Quite noticable. Good day. :usa

gulfcoastbeemer · Feb 26, 2008

Polarbear said:
My BMW Master Tech, has little regard for adjusting the bodies in perfect order, because it is not possible, without much hassle and doing it over and over, until you hit it dead on. ...You do your own and get it right and this is great. Do not expect any BMW mechanic to do any better, is where I come from.

I just did a service of my wife '05 R1200RT: valve adjustment, throttlebody sync, oil and filter change, new air filter and spark plugs -- it took me about 4.5 hours even with a helper. I don't think a BMW Master Tech would be allowed to spend as much time as I do on the tedious stuff like the valve adjustment and throttlebody sync.

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