The Art of the Synch

[rondob4]

My 99 RT was running rougher after the 12K service than before, particularly on the bottom end and at idle. I took it back to the shop and they spent a couple of hours on it, with the fix being to raise the idle a bit. A few days later I replaced the Bosch plugs with Autolites and the problem was largely cured.

 

About a month later it started idling roughly again, and it was suggested on this forum that I try carb cleaner sprayed in through the Big Brass Screw (BBS) port while running. I carefully marked the position of each screw in turns from lightly seated, then extracted each, one at at time, spraying the cleaner into the port while running at raised idle. Each BBS was covered in soot-like material and I cleaned them before returning them to their original positions. Bike ran pretty well.

 

I then decided to check the carb synch with my brand new TwinMax. I carefully followed the calibration directions included with the TM, then attached the hoses to the ports on the bottoms of each throttle body. The TM was balanced at idle and minimum sensitivity. As the sensitivity was raised to the 2 o'clock position, the needles shifted to the right to the 2 declination. Turning the sensitivity higher (to the 5 o'clock position) did not move it further. Running the RPMs to 4K and repeating the process also produced no changes in the needle positoin.

 

I followed the directions to gently turn and check the BBS on that side (the right side) and nothing happened. I turned the BBS the other direction with no change. I turned the BBS all the way in, no change (needle still at 2). I turned the screw back to the original position, no change. Again, at 4K RPM nada. I rode the bike and it feels fine, no noticeable vibration or strange feelings.

 

So what have I done wrong? The TM hoses slip rather casually onto the nipples; maybe they're not tight enough? Any suggestions out there as to why moving the BBS didn't change the TM readings?

[EffBee]

The Big Brass Screw (BBS) allows for air to enter the engine when the butterfly on that throttle body is closed. Therefore, it affects both idle and synchronization at idle and barely off idle.

 

Above that, the sync is affected by adjusting the throttle cables where the outer housing ends at each throttle body. There is a lock nut and an adjuster on each side. Just make sure that when you adjust them, that there is still just a touch of slack when you shut the throttle off. Otherwise the butterfly on that side is not closing completely.

[jslyter]

The hoses on the TwinMax should be very tight on the throttle bodies. My Twinmax came with adapter hoses with a smaller diameter than the ones that come straight off the Twinmax. The first time I used my Twinmax (not knowing which size hose to use), I easily slipped the ones without the adapter on and notice the same thing you did, basically nothing I did changed anything. I put the adapter hoses on and was able to adjust the throttle bodies per instructions. If you don't have a tight seal, you won't get an accurate vacuum reading.

[JamesW]

This sounds kind of similar to a previous thread not long ago. I still say adjust brass screws for best idle like mixture screws on old fashioned carbs the adjust throttle stop screws for sync at desired idle speed. What is desired idle speed? Answer: Whatever, be it 1K or 1.2K or?

[Tipover_Bob]

James:

No, brass bypass screws only provide volume, not mixture adjustment. The adjusting of the mixture is provided by the oxygen sensor and the computer. You change that with the map. So adjusting speed can be done with the brass bypass screws or with the butterfly stop screw. It's kind of an art with an early bike with the crossover cable. The later models with the cable splitter should be easier. However, I don't recommend you set your idle off the butterfly stop screw. It is the butterfly stop screw that sets the base idle and then final balancing is done with the brass bypass screws. Forget mixture. That is not done with these screwings.

Tipove Bob

[JamesW]

James:

No, brass bypass screws only provide volume, not mixture adjustment. The adjusting of the mixture is provided by the oxygen sensor and the computer. You change that with the map. So adjusting speed can be done with the brass bypass screws or with the butterfly stop screw. It's kind of an art with an early bike with the crossover cable. The later models with the cable splitter should be easier. However, I don't recommend you set your idle off the butterfly stop screw. It is the butterfly stop screw that sets the base idle and then final balancing is done with the brass bypass screws. Forget mixture. That is not done with these screwings.

Tipove Bob

 

OK Bob, let's say you are correct. And you may very well be. However, say one buys a pair of new TBs and installs them. How does one make the initial adjustment of the two brass screws? Also,for discussion sake, let's also assume we are talking about an 04 1150RT.

[Tipover_Bob]

OK Bob, let's say you are correct. And you may very well be. However, say one buys a pair of new TBs and installs them. How does one make the initial adjustment of the two brass screws? Also,for discussion sake, let's also assume we are talking about an 04 1150RT.

 

James:

I dunno. Just install them, set the TPS and left butterfly per the Lentini "zero-zero" method, set the BBSs out 11/2 turns each, adjust the right butterfly for balance, then adjust idle speed and further idle balance using the BBSs and then adjust 4000 rpm balance using the cables. Ka-ching.

Tipover Bob

[T__]

You don’t want to do a Zero = Zero on the adaptive 1150 TPS.. Zero = Zero is only for the 1100 non adaptive TPS..

 

Twisty

[ShovelStrokeEd]

-1 on the zero=zero. Not needed or recommended with an 1150.

If you buy the throttle bodies from BMW, they come as a matched pair and the throttle stop screws are preset on a flow bench to give even flow from both bodies. For various reasons of relative health of the two cylinders on the bike, that matched air flow may not be what the bike needs or wants. The bypass screws are used for final trim to give equal vacuum at each port. When replacing the TPS or putting an old TPS on a new throttle body, one simply sets a nominal voltage, anywhere from 200 to 300 mV, with the left throttle body fully closed. You then "teach" the system, via pulling the F5 fuse, replacing it and turning the throttle, with the key on, twice from full closed to full open and back again.

 

I am not a big fan of the TwinMax, much preferring a manometer to do this job. I use one with mercury in it but, in conscience, I cannot recommend that to anyone not trained in the handling of the stuff. For shop use, Dwyer Instruments sells a device called a Magnahelic which can be purchased as a differential vacuum gauge with + or - 15" mercury readings (adequate for TB synch) for not much more than a TwinMax. No batteries in it and no electronics to get out of calibration. It's a little bulky (about 6" in diameter and 2" thick) but can be set up to sit nicely on top of your tank filler using a towel to protect the paint.

 

For the true anal retentive, a water manometer is cheaper than all of this, can be made at home and is 13X as sensitive as a mercury manometer. I have never felt the need but, they are handy if you are the type who decides he needs to re-synch every week or so.

[JamesW]

Thanks Ed, that was good information especially the discussion about being a matched pair and adjusted on a flow bench. I think I must have just got lucky when I set both brass screws out one turn and then balanced idle with a slight adjustment to the stop screws. The idle is much smoother and no surging with or without the Techlusion. Think I will just go for a ride.

 

......In the morning

[Tipover_Bob]

You don’t want to do a Zero = Zero on the adaptive 1150 TPS.. Zero = Zero is only for the 1100 non adaptive TPS..

Twisty

 

Twisty:

I stand corrected.

Tipover Bob