setting idle speed on 1994 R1100rs

I adjusted my valves and did a throttle sync for the first time with excellent results--my idle speed is sitting just under 1,000 rpm and I'd like to set it a little higher (say about 11-1200)--when your turn the brass screws on the throttle bodies when synchronizing counterclockwise, the idle speed should increase. Do you find that they must be turned a lot to make a small change in rpm's? I was a little leery about going too far on my first attempt, but I'm game for anything. Any thoughts?
Tony

I find that I should get a response with as little as 1/4 turn. It is entirely possible and even maybe likely that the idle air passages are a little dirty. So carefully keep track of where the big brass screws are by turning them IN - keeping track of how much they screw in till just lightly seated. Then remove them.

Use just a little spray carb cleaner (I use Gumout brand) and compresssed air to clean the passage. Then thoroughly clean the tip of the screw needles. Re-install by screwing them back in until loightly seated and then back them each out the amount you went in when you started this procedure.

Then start the engine, let it warm up a little bit, and synchronize the throttle bodies at idle with an rpm of 1100 or so. I always set a fan blowing on the front of the engine when I do this. You should too.

It is a fine adjustment. There are conventional idle stop screws on the cable pulleys as well for gross adjustment. Mine still have the factory paint dot on them and they are in synch. It would be easiest to leave them alone and make do with the brass bypass screws if you can.
Mine sits right around 1250 when hot.

aapasquale said:

I adjusted my valves and did a throttle sync for the first time with excellent results--my idle speed is sitting just under 1,000 rpm and I'd like to set it a little higher (say about 11-1200)--when your turn the brass screws on the throttle bodies when synchronizing counterclockwise, the idle speed should increase. ..... Any thoughts?
Tony

Click to expand...

No! The Big Brass Screw allows air to enter the throttle body. If you screw it IN, clockwise, you are closing the passage and the idle speed should drop. You should increase your idle speed by slightly turning the BBS counter-clockwise.

Follow the advice you got above about cleaning the BBS and the passage, then try to set the idle again.

thanks guys
off to NAPA parts for Gumout carb cleaner and another foray into the unknown!
Tony

PGlaves said:

I find that I should get a response with as little as 1/4 turn. It is entirely possible and even maybe likely that the idle air passages are a little dirty. So carefully keep track of where the big brass screws are by turning them IN - keeping track of how much they screw in till just lightly seated. Then remove them.

Use just a little spray carb cleaner (I use Gumout brand) and compresssed air to clean the passage. Then thoroughly clean the tip of the screw needles. Re-install by screwing them back in until loightly seated and then back them each out the amount you went in when you started this procedure.

Then start the engine, let it warm up a little bit, and synchronize the throttle bodies at idle with an rpm of 1100 or so. I always set a fan blowing on the front of the engine when I do this. You should too.

Click to expand...

Hi Paul-
I got the carb cleaner, got out my scuba tank and regulator with air nozzle, and went after it. I checked how far in the brass screws were in so I'd have a point to return to and pulled out each screw in turn and cleaned the screws. They had some kind of black soot or carbon on them, but cleaned up easily. I sprayed the opening and blew out the holes on each throttle body. At this point I put the screws back in and reset them to where they were. The bike started easily and I proceeded to back the screws out (counterclockwise) a 1/4 turn at a time on each side. I expected the rpm to rise, but it didn't. In fact, I backed them out all the way while the bike was running and the bike didn't seem to notice at all! When the screws were totally removed, I could hear air being drawn through the hole into the throttle body, so I'm assuming that the opening was cleared with my cleaning. What am I missing here? The idle seems to up maybe by 40-50 rpm, but with those screws out as far as I had them, I would think the engine speed would be much higher.

As it stands right now, the engine is running very smoothly and once warmed up, idle speed sits a little over a 1,000 rpm. I still would like to know what the problem is though. Do you think that I should clean those openings more agressively? Does it hurt the engine to spray this cleaner into the opening with the screws out and the engine running?

Thanks for your time and expertise.
Tony

scott.lambert said:

It is a fine adjustment. There are conventional idle stop screws on the cable pulleys as well for gross adjustment. Mine still have the factory paint dot on them and they are in synch. It would be easiest to leave them alone and make do with the brass bypass screws if you can.
Mine sits right around 1250 when hot.

Click to expand...

DON'T mess with the idle stop screws on the cable pulleys, unless you know what you are doing and how to go about getting the TB's back in balance. I did mess with them some years back and it took a lot of diligent fiddling and help from Paul Glaves (technique) until I finally got them back and balanced. Now the bike idles smooth at 1000 rpm.

So do the idle adjustment with the BBS while using some form of balance device, like mercury sticks, or Twinmax.

Have to advise that you do NOT spray the cleaner in while the engine is running - it isn't fuel, it's solvent.

I've also used gasoline on a Q-Tip (several Q-Tips, actually), gently - this pulls the junk out instead of pushing it in. This picture is actual Q-Tips that I have used in this task.

Once the little passageway is Fully Open, backing the screw out has no more effect. From fully closed (lightly seated), three turns is about the max adjustment. If you suspect that it's still not quite right, you may need to have the cables re-balanced.

Also check that the O-rings aren't cracked - this will create a leakage path for air, which would make it more difficult to achieve and maintain proper balance. Do NOT put any grease - including silicone grease - on the O-rings: this will let engine vibration change the setting!

Pauls1150 said:

If you suspect that it's still not quite right, you may need to have the cables re-balanced.

Click to expand...

Just to be clear the throttle cables have nothing to do with idle air/RPM adjustment. The baseline setting is achieved by throttle plate adjustment (throttle stop screws and lock nuts) and the TPS voltage (.370 to .400) being correct. Normally the throttle stop screws which were set at the factory using flow metering equipment never need adjusting. They normally have a dab of blue paint locking them in place. Fine adjustment for idle RPM and throttle balance is achieved using the Big Brass Screws (BBS) and the orifice they screw into and the screws tips themselves need to be absolutely clean for best results.

Once this is all done and correct then you adjust the throttle cables for off idle balance. I check them just off idle and around 4K RPM. This is really fiddly sometimes but well worth the time and effort to get it bang on to reduce surging and other annoying issues. And as Paul already stated, put a big fan in front of the bike while you do all this work so you don't overheat the motor.

Pauls1150 said:

........snip .............

Also check that the O-rings aren't cracked - this will create a leakage path for air, which would make it more difficult to achieve and maintain proper balance. Do NOT put any grease - including silicone grease - on the O-rings: this will let engine vibration to change the setting!

Click to expand...

I have been very lightly coating BBS O-rings with dielectric grease for about 80,000 miles. I have never had movement of the BBS. I could see this happening if grease is allowed to migrate to the threads of the BBS.

Stickier thicker stuff... hmm, maybe ok. The silicone grease I used (since they're rubber rings) caused some wonder (and wander) for a bit, so I made a poor choice.

Ah yes, once again we see the Holy Paint on the screws... The TB's are set up on a fixture, assembly-line style, at the factory; they are not set up on each motor individually. So, there is no compensation for "your" particular intake plumbing, exhaust plumbing, valve clearance, or colored map plug.

How is this known? Because of the BMW statement that if the paint is broken, they want you to send the throttle bodies back to Germany.

If you set the left side to 0.380 volts at idle (the only specs I've seen say .360 to .400), and then set the right side to match that, you can get a little closer in the balancing act. If you take a little extra time and go back and forth between the BBS's and the right stop screw, you can make your two columns of mercury (or other juice, or LCD display) track each other very closely indeed.

I also recommend that instead of 4000 rpm, the cable balance be done at 2000-2500 rpm: the smaller throttle opening will make any difference in vacuum more perceptible.

Yeah, holy blue paint indeed. I wonder what Bing agencies does when you send them a TB for a rebuild. Do they use a flow bench? I bet they have a simpler procedure but I would be curious to know.

I've done the zero=zero procedure on a few bikes now and with patience it does work. In fact I've never been able to achieve a proper balanced idle without using the TPS voltage as a guide. I set it to .0010 VDC with the stop screw backed way off so the throttle plate is totally closed and then using a 4 digit voltmeter to advance the idle stop screw until the TPS reads .370 to .400 VDC. With the BBS screws totally closed I then fire the bike up and balance the right side stop screw to perfect balance with the now preset left side. Then I open the BBscrews 1.5 turns (for 1100RT) and balance idle again. Should be 1000 to 1100 RPM. If everything is right the BBScrews can be used to fine tune the idle.

Then balance just off idle using the throttle cable adjusters (around 2000 to 2500 as stated above) and then check the balance at 4000. There are sometimes minor trade offs to get it right depending on how old or sloppy your cables are. Average vacuum on both sides is the key here.

I've tuned up several bikes quite a few times this way and it works. Fear of "cracking the blue paint" is unjustified as is BMW advice to send em home IMO.