Poor Gas Mileage

["Tom Brown" <tbrown@xxxxxxxxxxx>]

Peter:

This is a lot better information!

The bad vibration can indeed be caused by the thottle bodies being badly out
of synch.   If you've moved the gas tank or done any other work near the
right side throttle body, it's possible and common to pull the throttle body
cable out of it's adjuster end.  This will make the bike run quite rough.
In that case, just shut off the bike, find the cable and replace it in the
fitting.  It's easy to spot if you know to look for it.

The early oilheads do have a different throttle linkage that tends to need
adjustment more often, but it is not "defective".   In fact, some people
prefer it.

Replacing the cables doesn't really improve things unless your cables are so
bad that they're starting to shred, which is not unbelievable on a 9 year
old bike.  Corrosion or some other gremlin could have been working on them
inside.   It's not a terrible idea to replace the cables.  It may save you a
bad time on the side of the road some day.   For that reason alone, I'd do
it.  This is a great time to change them, while you can't ride.

A careful (anal?) valve adjustment is the first step to a good throttle body
synch.

After you have confidence in your valve clearances, you can do a quick
throttle body synch in about 5 minutes to smooth out your bike.   The
mechanic can probably show you how.  It's not difficult on an RS because you
can reach everything without removing any fairings.  This shouldn't need to
be done more then once every 3,000 miles or so and your bike shouldn't be
running "very rough" at this point.  You should know how to adjust the synch
if you're riding a bike with this old style linkage.  (FYI: No, it's not a
good idea to try and update your bike to the new linkage.)

I'm not really sure why the mileage would drop after your mechanic synched
the throttle bodies.  That doesn't really make sense to me.  Perhaps some
other adjustment was been made at the same service...like to the TPS sensor
position?

The older throttle control system has a long cable going from the throttle
control (handlebar grip) to the left side throttle body.  There is a
throttle wheel that is moved when the cable is pulled.   A second cable is
also fastened to this moving wheel.  This shorter cable runs between the
left side and the right side throttle bodies essentially linking them
together.

Adjusting the length of this left to right linking cable is what synchs or
unsynchs the throttle bodies.   The critical adjustment is just above the
right side throttle body near the fuel lines and fuel injector.  It's just a
single black covered cable with a threaded adjuster piece and a lock nut on
the end.   You loosen the locknut and turn clockwise to make the cable
longer and counterclockwise to make it shorter.   When it is the proper
length, the thottle butterflies inside the throttle bodies will open exactly
the same amount with a pull of the throttle and the bike will run smoothly.
(It's not quite as simple as that, but basically, that's the goal here.)

How do you know when the cable is the correct length?  You attach a vacuum
gage to the bottom of each throttle body and compare the readings.  When the
readings are the same for both sides, theoretically, the throttle cable is
exactly the correct length.  These vacuum gages go by many names and types.
"Twin-Max", "Mercury Manometer", "Carb Stix" are a few common ones.  I have
a Twin Max and can't seem to get a good synch out of the thing.   I bought a
mercury type gage last year and it works great.   There are some other kinds
as well, but they all do, or are supposed to do, the same thing; measure the
vacuum in the throttle bodies and give you the relative difference.

Now, you have to understand that, at idle, the throttle cables are loose.
The throttle wheels rest on "throttle stops" at idle.   Since what you're
really adjusting is cable length, you have to twist the throttle just enough
to assure that the throttle cable is actually working the throttle.   Hold
the engine at 1500 to 2000 RPMs during the adjustment.   A Throttle Meister
or Wrist Rest is damned handy for this, but you can jam something (I've used
Popsicle sticks) between the throttle grip and the switch box on the
handlebar.  A large vice grip with a rag in the jaws loosely applied will
also do the trick.

This is a very basic instruction to get your bike close.  If you want it
perfect, you gotta know more theory and I have to write a lot longer
message.

STUFF YOU NEED:  You need to have a fan in front of the bike to keep the
engine cool.  I use a big, cheap window fan on the high setting.  You need a
mercury manometer or one of the other kinds.   You need a 10mm open end
wrench.  You need something to hold the throttle.   That's about it...after
someone has adjusted the valves perfectly for you.

Anyway, when you have all this in order, you adjust the length of that cable
on the right throttle body until the vacuum gage readings match, then snug
down the lock nut (Don't overtighten and booger up the threads.  That will
make future adjustments more difficult.  Minimally snug is just fine.).
Your bike should be smooth for 3,000 miles or so.

FYI: The newer oilhead throttle control system has a cable running from the
throttle control to a central distributor box.  This cable pulls on a wheel
inside the box.  Also fastened to this wheel are two smaller cables.  One
small cable goes to each throttle body.   This control box is a nightmare to
access and work on, but it seems to hold settings better than the old
system.  The synch adjustment is in the same spot on both systems, cable end
on the top right side throttle body.

FYI: I have a friend with a 2000 RT with the same setup as you (Remus and
pulled CCP - Not sure if he has a Pot or not, I think he may.).  He gets
mileage in the low 40s or high 30s on the highway depending on how and where
he's riding.   Stock bikes will do a bit better on economy, but he likes the
sound of the Remus touring pipe and the engine response.   I do too.

Good luck with the election hazards.  You'll be in my thoughts and prayers.
A.B.B., baby.

- -TB


>Thanks for the responses. To clarify, I have never had a problem with
surging. When I bought the bike it was stock. I put on the Remus and
followed the list suggestions about pulling the ccp and resetting the
computer. The oxygen sensor is still in place. I didn't notice the bad gas
mileage until, because of bad vibration, I took my bike in to have the
valves adjusted and my mechanic (not dealer) suggested syncing the throttle
bodies.  Afterwards, the vibration was gone, but the gas mileage had
dropped. Then it started vibrating again. I took it back and my mechanic
said the throttle bodies weren't staying synced and asked if I had ever
replaced the throttle cables, saying something about the '95 cables being
defective. He suggested changing the cables this winter. I am sure that my
gas mileage was not this bad before the valve adjustment/throttle body
syncing. I am in Laconia, New Hampshire, so if any of you are local and
knowledgable about these issues, please let me know. I can't ride now, not
just because it is cold, but also because there are so many candidates and
staffers on the roads, it's dangerous.
Thanks, again.
Peter

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