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RE: oilheads-digest V2 #32

Tom Brown wrote a lot of very sane, very good advice. But I do have my own

First, for those who may be reading and not be aware, I am not an oilhead
newbie nor a boxer newbie. I've got nearly a quarter million miles of BMW
boxer riding experience, and in that time I've done virtually all my own
maintenance on 2 different airheads and one oilhead. My R11RS is a so-called
"beta" bike (build date 1993.05) and I am the original owner. It now has 73k
miles. With the exception of the break-in maintenance, internal transimission
work (input shaft replacement) and a cylinder head gasket replacement (while
on warrantee) I have done all of the work on this bike, which includes a
clutch replacement, the other cylinder gasket replacement, a starter motor
rebuild, and removal of the ABS system. All such work now has sufficient miles
on it that there's no question it was done correctly.

Call it a chip on my shoulder but I think I know what I'm doing, and that I
know what I like.

>Date: Sat, 5 Feb 2005 09:57:10 -0600
>From: "Tom Brown" <tbrown@xxxxxxxxxxx>
>Subject: Carbs etc.

>I think you're entering a whole new world trying to put carbs on an oilhead.

No doubt! But I keep stressing, I don't want to be a pioneer. I think people
have done this before and might very well have developed excellent solutions.
I just don't know their e-mail addresses.

>Be prepared to replace the motronic completely with analog ignition etc.
>All the fuel curves etc are going to be completely wrong.

I'm not at all sure about that (but I don't know what I don't know). I DO know
the "fuel curve" would be a non-issue. The fuel pump will simply go away,
which will a) make the bike a few grams lighter, b) give me a few cc's more
fuel capacity, c) be one less thing to leave me stranded on the roadside, and
d) greatly reduce the probability of my externally-mounted fuel filter
exploding. All Good Things.

Fuel would be supplied to float bowls via gravity feed. "Fuel curves" would be
provided by the carburetor jets and the needle (that's what they're for). If
the Motronic was still energized and felt it needed to send more or less fuel
thru the injectors, based on whatever information it was collecting at any
given millisecond, it really wouldn't matter since there would be no
The real issue would be the IGNITION curve. I have no idea if that would be
right. But let's think about it:

Replacement of the carbs would result in the disconnection of the Throttle
Position Sensor (TPS) and injectors. The airbox sensor and O2 sensor would

My assumption is that even with TPS and injector connectors dead-ended the
Motronic would still generate a spark at some point during each crank
revolution (every other one, in a given cylinder, being the usual "waste
spark"). That seems like basic limp-home functionality which I assume Motronic
provides. Would it advance properly? Perhaps not. But is there any kind of
vacuum sensor feeding information to Motronic? Not to my knowledge. Does
Motronic use TPS data to alter ignition timing? Possibly. Does it use
information from the airbox and/or O2 sensors to make ignition timing
adjustments? Possibly. Does Motronic make advance adjustments based on RPM? I
assume it must.

Is ignition advance based ENTIRELY on RPM? I dunno; seems simplistic so I
doubt it. But perhaps all those sensors exist simply to provide data for the
FUEL curve...which again, I no longer care about. Maybe ignition timing is
based entirely on RPM + O2 + airbox sensor value, wouldn't that be nice? In
that case as long as the carbs made the engine speed go up and down when I
wanted it to, and the mixture was close, the Motronic would provide a spark
exactly when it should. In fact, unless the ignition curve is weighted HEAVILY
to TPS value, it seems plausible to me that it might continue to work properly
or at least acceptably.

But I may be dead wrong. This (aside from exact jetting specs) is the single
biggest mystery (to me) about the concept.

But again, I assume that for some, these mysteries have already been solved.

>As far as your fear that the throttle bodies need to be adjusted all the
>well, that's just not true.  You need to adjust when you adjust valves
>because changing the valve clearance affects the vacuum in the throttle
>just as it would in carbs.

I disagree. One of the most delightful things about the oilhead engine is how
well it maintains valve adjustment compared to an airhead. While the bike was
still on warrantee, I used to check my valve adjustment every 6k miles. But I
found I rarely had to touch them, even when the engine was new and I fully
expected some "settle in". Since the warrantee is up I only check them every
12k miles and still rarely need to fiddle.

I DO know how to adjust the valves. When I brought the bike home from the
break-in maintenance, I noted that if I leaned to the right, the sound of the
valves was different than if I leaned to the left. "I don't know if either
side is actually OUT of spec", I thought to myself, "but I DO know that I can
at least get them the same." And I did just that. I adjusted the valves myself
the next time and it was by far the most adjustment they have ever required,
and yes when I was done they "sounded" the same no matter which way I leaned
as I was riding.
At 73k miles with no valve problems, and with "surging" having been at times
noticeable but by no means as severe as many others on this list have
reported, one can assume I'm "good enough" at adjusting oilhead valves.

Now, having said all that, let me add that many times the bike would begin to
surge, and/or would lose fuel economy, and/or would run rough, whatever. By
fiddling with the damned Bings (and ignoring the valve adjustment which a few
thousand miles later would prove fine) I was able to get it running right
again. That was when the Bings were still new, of course.

Let me also mention (again) that this is the WORST STARTING STREET BIKE I HAVE
EVER HAD, AND HAS BEEN SINCE DAY 1. Fuel injected motors are supposed to be
"don't touch the throttle, just punch the start button". But it is common,
probably universal, among oilhead owners to have developed some kind of
throttle gyration just to get the bike started.

My particular method is throttle wide open CRANKCRANKCRANKCRANKCRANKCRANK snap
throttle shut.

What's yours?

I have to crank the starter of this bike 3x-5x more than any airhead I ever
had. My airheads, when properly tuned (even with Bing carbs) would start on
the first ignition stroke; you'd never even hear the starter motor. This is an
aspect of my oilhead that has always pissed me off. My theory (and it is only
that) is that the Motronic deliberately delays starting. You crank it a few
times until the Motronic figures out what the conditions are, decides what to
do, and then grudgingly provides a spark and/or fuel. Note I'm not blaming the
Bings for this particular characteristic (though it wouldn't surprise me at
all to find they are at fault).

>When you synch, all you're really doing is
>adjusting the length of one throttle cable so the vacuums match on both
>This doesn't take long and isn't needed that often.

Yes, I understand. However our definitions of "too long" and "that often" are
not the same. I feel that the right side thottle being a slave to the left is
inherently problematic. And I regard the adjusters as an ergonomic PITA.

>[snip] These bikes are very smooth by comparison.   The
>bit of vibration you do feel can be eliminated by careful tweaking, but it's
>not likely to be any different with different carburation.

I agree these bikes are remarkably smooth for big bore twins (near-perfect
primary balance being the reason). The fact that it isn't as smooth as a
K-bike is in fact one reason I like it. Before I bought my oilhead I test rode
a used K100RS. It ran beautifully. I found it boring. I would have bought,
then and there, the Euro-spec R100RS that was also on the lot. However the
R100RS was already sold. I waited a year or two and the R1100RS came out. It
took me all summer of 1993 to make up my mind ("I know what an R100RS is all
about. Will the R11 be shade-tree wrenchable? Will it be reliable? At least it
doesn't have Bing carbs...").

Seriously, three things were major contributors to my decision to buy the
oilhead. 1) If I buy an R100RS, I have to buy a set of carbs to replace the
Bing CVs. 2) If I buy an R100, I have to drill an oil filler hole in the
rocker cover and come up with a decent cap-plug for it. 3) If I buy an R100, I
have to engineer some kind of oil sight glass.

Knowing (or thinking I knew) that the R11RS "solved" those three issues were
part of the reason I decided to buy it. The night-and-day difference in
performance was the big reason, of course. But once I decided I never
regretted it. To my delight I found it every bit as shade-tree wrenchable as
an airhead. My R11RS is the best bike I've ever ridden BAR NONE.

Note however I've deliberatly avoided riding things like Ducatis and
high-performance UJMs, which might tarnish my satisfaction.

But I'm not talking about "a bit of vibration" here. I'm talking about lousy
starting, frequent need for adjustment, not particularly good mileage, poor
durability. By the end of last season my bike was unrideable. I admit I was
dumb to not diagnose the root cause far sooner (I was pissed that I had to
deal with such a problem at all, and was disinclined to put time into it); but
my original suspicion that it was a Bing problem certainly proved correct.

And you have to understand my perspective here: all of the problems I've just
listed are ABSOLUTELY TYPICAL of my experience with Bing fuel mixers. And I




Whether replacing the throttle bodies on my R11 is a good idea or not is
certainly an open question, but my experience with Bings to date--INCLUDING
the ones on my R11--is not.

>If you're just looking for more power, like for racing, this may be a good
>to go.  In racing, you're not concerned so much with low end torque,
>smoothness at lower speeds, the ability to idle smoothly without stalling or
>hunting etc.   Many of the fastest race bikes run like absolute crap at sane
>speeds.    It's not a priority.

You are absolutely right. It is entirely likely that whatever these "Euro
go-fast boys" have come up with would not idle, would get lousy mileage, would
be rough at anything less than 5k RPM, and would have none of the good manners
which this bike, when new, had in spades.

But it's also entirely possible (and I think likely) that this purported 108
HP recipe, when dialed down a bit, might yield exactly what I'm looking for.
I'm not dying for more power, I'd be happy just to get my original performance
back. But I sure wouldn't mind another 10 HP, if it didn't come at the price
of reliability and ridability.

>If this is your main street bike, my advice is to stick with the stock stuff
>and maximize your enjoyment of it by eliminating the surge problem and
>it synched and tuned.    If it's more of a toy or science project for you,
>well, go for it.   Who cares if it won't run?

No, my bike isn't a toy or a project. It's my ride to work in the summer and
used to be how I spent my vacations (I hope it will be again). It's very
important that it runs well in the real world. But keep in mind, it could not
possibly run worse than it did last season. At one point I seriously
considered taking the 26mm DellOrtos from my R60, wrapping the intake bosses
with duct tape until they were big enough to clamp into the R11, and simply
seeing if it would idle. If so, it would have been a 500% improvement.

>To equate the motronic/throttle body system with Bing carburators of old is
>not valid.   There is a bearing, especially on the right side throttle body
>that can go out and cause the bikes not to synch well and make a little
>rattling noise on the right side.    This can happen on high mileage bikes.

Bearing, schmearing. There's always a reason, usually several, that Bings
don't work well. Frankly, with carb/carb swaps it was simply that other makes
were  designed and/or built better. Nobody would make the argument that a Yugo
is built better than a Honda, and I think you'd be wrong to argue Bings are
built better than Mikunis. True, arguing Bing THROTTLE BODY < Mikuni CARB is a
bit like arguing Apples < Oranges. It's probably even more like arguing Horse
Apples < Oranges.

>Just replace the throttle body or the bearing if you can find one and be done
with it.

Well, that's what I've just done; it was finally warm enough yesterday to work
out in the garage. Actually I replaced just the right-hand shaft. When I got
it apart the bushings didn't look all that great but it went back together
that way anyhow. The rattling has gone away for now but I expect it to be
back, probably with rattling on the left side to match. But at least I got the
bike to idle (though not all that well). Hoorah.

It was cheap and expedient and far easier than installing a
perfectly-engineered Mikuni kit would have been even if such a thing existed.
But I do not expect long-term satisfaction, and until I do the 0=0 schtick I
still won't know for sure where I'm at.

...which is what I should have done today instead of all this exposition...!

>These are great bikes...

I agree completely. There's no question it was the best possible bike FOR ME
from the day I bought it until the turn of the century, and there's every
possibility, with a bit of tuning up, that it will continue to serve me well
into this one.
I argued that when it came out it the R1100RS was best production motorcycle
ever built, and I believe that.

And I do want to love it again.

>...the way they are.

Again, we differ. As I mentioned earlier, I find the oilhead to be eminently
shade-treeable and by tweaking it I have made what are for me, substantial
improvements. My favorite example is my decision to remove the ABS. This is a
subject all its own which has already been beat to death. The point I want to
make from it is that once I had done it, the results did not exceed my

They MET my expectations.


I got PRECISELY the results I expected and desired. This is an example of how
well I know the bike, and how well I know my own preferences.

Had I decided to leave it "the way it was" I would have denied myself the
single biggest improvement I have made to the bike.

>Learn to get the most out of them and you'll be pretty thrilled.

I spent several years and tens of thousands of miles being totally thrilled.
Then I spent a few years and a few thousand more miles being blase. And then a
couple years becoming progressively more pissed-off (thank you, BING).

I hope that yesterday's repair and tomorrow's tuning will again make this a
thrilling bike. It's possible.

But I have, MANY times in the past, been thrilled by the difference between a
motorcycle with Bing and that same motorcycle with Mikuni|Lectron|DellOrto.

That is ALSO possible.

John D