throttle body adjust

[JamesW]

My 04RT has always had a tendency to surge ever so slightly at slow speeds in low gears and the idle has never been constant or smooth since day one. Now I have used a twin max for accurate TB balancing and I have done maticulous valve adjustments and still the machine has had this slight tendency to surge at slow speed. So, a couple of months ago I bought a Techlusion R259 which did seem to help smooth the idle and surging was reduced. I noticed that the exhaust began to smell of un-burned fuel and the plugs had darkened (black)considerably. I began to think about the throttle bodies and how to adjust them and came up with this procedure; (1)Remove the brass screws, clean them, re-install and turn them in untill they seat then back each out exactly one full turn. (2) Warm up the bike and with Twin Max connected balance throttle bodies at idle using the throttle stop screws only NOT THE BRASS SCREWS. When finished make sure throttle stops are both contacting the stop screws when at idle. (3) Run up to about 3K RPM and adjust sync with throttle cable adjusters. When I finished with the TB adjust guess what? No more surging, smooth idle for the first time in 25K miles, was able to re-adjust Techlusion for less rich at idle. I could have maybe saved my money and not bought the Techlusion but it does add a bit more fuel when accelerating which I kind of like but could easily have done without. I called Bing Agency and discussed this method of TB adjust with them and they agreed. The thing to keep in mind is that the brass screws are mixture adjusts and should not be used to balance TBs. Balance is achieved by adjusting the stop screws. Anyone with airhead experience with the old Bing CV carbs will see a similarity with this method of TB adjustment. Oh, before I removed the brass screws for cleaning I seated them and made note of where they were set. The left TB brass screw was out about 3/4 turn while the right was slightly less than 1/2 turn. No wonder the bike ran lean.

[Rydrhard]

I USED A SLIGHTLY DIFFERENT WAY TO SET UP MY 1100RT. I USED THE THROTTLE STOP SCREWS TO GIVE ME A MINIMUM IDLE SPEED OF ABOUT 800RPM. I THEN SYNCHED THE THROTTLE STOP SCREWS, SO THEY WERE OPEN THE SAME AMOUNT. I THEN SET THE TPS TO .385VOLTS. SYNCHED THE THROTTLE CABLES AT 1500RPM RECHECKED AT 2500RPM. FINALLY SYNCHED THE BRASS SCREWS TO GIVE A 1000RPM IDLE. I TOO HAVE A SMOOTH IDLE AND CRISP ACCELERATION.

[Tipover_Bob]

James:

I believe you when you say you got some good results, I just don't believe you accomplished it with anything but luck. I fail to see how you got the throttle bodies to rest on the throttle stop screws when you balanced with the cables, again luck must have been involved? Also, them there brass bypass screws have nothing to do with mixture to the best of my understanding. I think you better re-think your procedures.

Tipover Bob

[TREE]

Two small points..... the throttle stop screws are set at the factory on a flow bench, BMW says not to adjust them. That's why they have some green locktite.

The brass air screws are air not fuel, back them out and it gets leaner, in for richer. The fact yours were 1/2 and 3/4 turn does not = lean.

Correct me if I'm wrong, been a while.

 

Ignoring the above, I have used the throttle stop screw on the right to sync up my twin max on the stops but they recommend the airscrews for that.

The twinmax should give you a reasonable sync just like a flow bench IF the left is on the stop while you sync the right.

[thencamebronson]

James:

I believe you when you say you got some good results, I just don't believe you accomplished it with anything but luck. I fail to see how you got the throttle bodies to rest on the throttle stop screws when you balanced with the cables, again luck must have been involved? Also, them there brass bypass screws have nothing to do with mixture to the best of my understanding. I think you better re-think your procedures.

Tipover Bob

 

The stop screws are touching at idle. To adjust the cables you rev to 3000/4000 so they aren't supposed to touch the stop screws.

 

I had some of the same problems along with the bike "loading up" and dying at idle. I posted over at the Oracle RS board and learned that my biggest problem was a K&N air filter that was over oiled. Went to a BMW paper filter and solved most of my problem. Also used the stop screws to set the idle and adjusted the cables at 3000 and checked at 4000. The results were great. Went to Falling Leaf Rally last weekend and for the first time in a long time my hands aren't still tingling.

[Ken H.]

I USED A SLIGHTLY DIFFERENT WAY TO SET UP MY 1100RT. I USED THE THROTTLE STOP SCREWS TO GIVE ME A MINIMUM IDLE SPEED OF ABOUT 800RPM. I THEN SYNCHED THE THROTTLE STOP SCREWS, SO THEY WERE OPEN THE SAME AMOUNT. I THEN SET THE TPS TO .385VOLTS. SYNCHED THE THROTTLE CABLES AT 1500RPM RECHECKED AT 2500RPM. FINALLY SYNCHED THE BRASS SCREWS TO GIVE A 1000RPM IDLE. I TOO HAVE A SMOOTH IDLE AND CRISP ACCELERATION.

Well I'm glad you feel it works for you, but I would caution the general population against taking that approach. The relationship between the left idle stop screw and the TPS, regardless of the TPS voltage used, sets the baseline fuel map for the entire RPM range. Someone can back themselves into a mess pretty easily by fiddling with the left side stop screw.

 

BTW all upper case letters on a forum means YOU ARE SHOUTING.

[Tipover_Bob]

The stop screws are touching at idle. To adjust the cables you rev to 3000/4000 so they aren't supposed to touch the stop screws.

 

Bronson:

I am not sure of the exact relationship between the two throttle bodies and the crossover cable or dual cables of the newer bikes. However, If you have a crossover cable type setup and you set the left throttle butterfly on the throttle stop screw, it would appear possible that the crossover cable could hold the right butterfly off of its stop. I guess this would never be a problem with the dual throttle cables. For that reason I am careful to make sure the right butterfly is resting on the throttle stop rather than the crossover cable. This may require a slight opening of the right butterfly over the opening on the left butterfly compensated by a slight closing of the right brass bypass screw over the left bypass screw. Then of course, using my home-made balancer, I make sure the throttles are balanced at 4000 rpms.

Tipover Bob

[JamesW]

Hi Tipover, I agree that the brass screws are air adjust not fuel but the end result is mixture (air/fuel) ratio adjustment. I think next time I attempt this I am going to set the brass screws one turn out from seats then adjust each one for lean best idle then balance with stop screws.

Oh, when I was finished, I made sure the stop screws were contacting their respective plates by sliding a piece of newspaper between the screws and plates with the throttle fully closed. At idle the throttle cables both are slack so no problem there. I do agree with the person that said I was lucky to get good results by just turning the brass screws out the one full turn. I should have gone from the one full turn to lean best idle. I thought the way to sync TBs was to adjust only the right side brass screw and never touch the stop screws. This I got from reading posts on the internet. I really question the source of this info after seeing the results I got especially after talking this over with a guy at Bing Agency. Keep in mind that I have an 04RT and this must be a different critter than an 1100 that gets into a voltage adjustment procedure.

 

The thing I really can't get over is the smoothness no matter cruising at 4K or winding her out to 6 grand. I would go up against a stock 1200RT anytime.

I'll stay clear of 4.6L Ford Mustangs though

[T__]

I think you guys are misunderstanding the function of those brass air by-pass screws.. They neither richen or lean out the mixture under normal warm engine operation.. All they do is allow more or less air to enter the intake manifold & most of that effect is only at idle or low throttle openings.. For most warm engine operation the 02 sensor controls the fuel air mixture.. If more air is added with the brass screws the 02 sensor just tells the fueling computer to add more fuel to go with the added air.. If less air is added with the brass screws the 02 sensor just tells the fueling computer to remove a little fuel.. The 02 sensor & fueling computer hold the fuel air mixture pretty darn close to 14.7:1 for all warm engine idle & most warm engine off idle operation.. Adding more air with the brass screws will raise the idle speed on a warm closed loop engine but not change the fuel/air mixture..

 

The 02 sensor is the ONLY thing that controls the fuel air ratio while in closed loop (that IS the definition of close loop) .. The 1150 BMW is in closed loop for almost all warm engine operation.. Even at idle, light cruise, light acceleration, just off idle, in the surging range, at freeway speeds.. It will drop out of closed loop on a hard acceleration after about 5-10 seconds & will drop out of closed loop at about ¾ throttle but there is even a slight delay factor there also..

 

Even pulling the pink CCP on the 1150 BMW boxer doesn’t force open loop idle (it does force light throttle open loop off-idle to about 15% throttle though).. With no CCP (or the green CCP) drastic brass air by-pass screw tweaking can alter the open loop light throttle fuel/air ratio just slightly..

 

The above ONLY applies to the 1150 NOT the 1100 BMW boxer..

 

Twisty

[Ken H.]

They neither richen or lean out the mixture under normal warm engine operation.. All they do is allow more or less air to enter the intake manifold & most of that effect is only at idle or low throttle openings.

I have to disagree. Try this experiment yourself - Get an 1100 or 1150 at best higher RPM sync as you can. Now with a sensitive sync tool attached, hold the bike at a steady higher RPM (3K or something) and reach down and turn one of the brass screws. You will be amazed at how much the sync will change.

[T__]

They neither richen or lean out the mixture under normal warm engine operation.. All they do is allow more or less air to enter the intake manifold & most of that effect is only at idle or low throttle openings.

I have to disagree. Try this experiment yourself - Get an 1100 or 1150 at best higher RPM sync as you can. Now with a sensitive sync tool attached, hold the bike at a steady higher RPM (3K or something) and reach down and turn one of the brass screws. You will be amazed at how much the sync will change.

 

 

Ken, OK now try this,, get yourself a not so sensitive sync tool & do the same experiment.. You will then see the sync change at idle & low throttle openings but less or none measurable at higher throttle plate openings.. Keep in mind here your so called test is at a static no load (3K or something) not at road load (3K or something) so the throttle plates are only open a little bit at NO LOAD (3K or something) as opposed to open farther at road load (3K or something)..

 

Obviously the air by-pass circuits parallel the throttle plate air passages so they will always flow a little air even at WOT but the percentage of by-pass air is so small at moderate & up throttle plate openings that is insignificant..

 

I didn’t say the brass screws didn’t effect the higher throttle opening air flow I said it has the most effect at idle & low throttle openings (what part of that statement don’t you agree with?).. As the throttle plate is opened farther the small orifice of the by-pass screw circuit supplies less & less of the entire percentage of the total air flow..

 

Twisty

[Tipover_Bob]

They neither richen or lean out the mixture under normal warm engine operation.. All they do is allow more or less air to enter the intake manifold & most of that effect is only at idle or low throttle openings.

I have to disagree. Try this experiment yourself - Get an 1100 or 1150 at best higher RPM sync as you can. Now with a sensitive sync tool attached, hold the bike at a steady higher RPM (3K or something) and reach down and turn one of the brass screws. You will be amazed at how much the sync will change.

Ken:

I have to agree. Those brass bypass screws used for balancing and adjusting idle speed really change the 4000 rpm balance more than one would guess.

Tipover Bob