Updated to include the TPS Screw Method
2005 MOTO GUZZI BREVA NEVADA
Moto Guzzi Breva/Nevada 750. Donít matter what you call it, its all the same: throttle plate synchronization, or cylinder synchronization, or throttle position sensor (TPS) adjustment, or throttle butterfly adjustment. Probably able to adapt this method to some other models as well. Electronic Fuel Injections systems are much more sensitive than carburated bikes. To start the setup you will need a very accurate way to balance the throttle butterflies. (Professionals Refer to them as throttle plates, and since Iím not a professional who cares) I use a Twin Max electronic balancer (About $90) Very nice and very sensitive. Basically just measures the vacuumed in each throttle body.
The throttles butterflies should be balanced whenever anything is changed, such as when the valve clearances are adjusted. Balancing the butterflies is also commonly referred to as Cylinder Synchronization. Always adjust spark plug gap and valve clearances before adjusting the throttle butterflies.
The amount of air which is delivered at idle is determined by: 1. Throttle butterfly idle stop screw which holds the throttle butterfly slightly open and: 2. The idle bypass screws. The throttle butterfly idle stop position is set at the factory using an air flow bench method which precisely controls the amount of air flowing through the throttle bodies at idle. Except in very unusual circumstances you should never need to adjust the throttle butterfly idle stop screw which limits the rotation of the butterfly toward the totally closed position.
There is a throttle position sensor (TPS) located on the right throttle body.
The injection system primarily uses two inputs to determine how much fuel to deliver each time the injectors open and squirt. 1. How wide open the throttle butterfly is (throttle position) 2, How fast the engine is running (RPM). At a cold start up it also uses the cylinder temperature sensor. There is no direct measurement of air flow. It is computed. (Mapped) The TPS is a variable resistor which tells the injection systems electronic control unit (ECU) how wide open the throttle is. Since there is only one TPS, the system assumes that the left throttle body is synchronized to the right throttle body and that they are both delivering the same amount of air.
Whatís really cool I think is that as the throttle butterflies begin to open, that opening is measured in electricity. (Mvís, or Millivolts) as it opens wider more MVís are sent to the ECU for input. Add that input and the RPM input, Cylinder Temperature input, CO2 input, outside air temp input and probably a few other inputs. The ECU analyzes all this in one cazillionth of a nano second, and that tells the injectors the exact amount of fuel to inject into the cylinders. All this is called a Map. The map says when the throttle is open this much and your rpm is this much, and the outside air temp is this much and all the other inputs have their say, then this is how much fuel is going to be delivered. It takes a rocket scientist to figure all this out! Software is available to change your map should you want to or need to such as maybe when you get easier breathing exhaust coupled with a new easy air flow cleaner and so forth. They got this down. Itís way beyond my comprehension. As for me I will just stick to the stock apparatus. One more thing, the throttle butterfly stop screw. Basically it just prevents the butterflies from completely closing. If they completely close your bike would pretty much gag and puke all the time when you return to idle. These are set slightly open by the Rocket Scientists who used a mathematical equation using all the inputs and their bench air flow method. Measured in MVs precisely and not by vacuumed. This is an extremely critical measurement. Most shops have a small Axone diagnostic computer with your Moto Guzzi model software map installed to reset your idle screw to the proper MVís. Or some other capable type of computer. These little computers measure precisely at all throttle openings. But for the Idle, donít even think adjusting the idle stop screw.
1. Properly connect your Twin Max Carb Balancer and calibrate. Pretty simple, follow instructions.
2, Start the engine. Bring the engine to the prescribed temperature: *(122 degrees F 60 degrees C) No big deal on the temp. Just thought I would throw their figures in there.
3. Completely close the 2 bypass screws on the throttle bodies. Getting to them is a lot easier said than done. See picture #2 also. Turn them in counting the turns until closed. Write it down. Ignore the fact that is runs worse. The Throttle bodies must be adjusted to a very fine degree of balance.
4. Bring the engine to 3000 rpm +/- 300 rpm and hold
5. Check Butterfly balance using Twin Max Carb balancer
THERE ARE 2 WAYS TO ADJUST THE (TPS) BUTTERFLIES.
METHOD#1 THE EASY WAY.
METHOD#2 MORE DIFFICULT BUT STILL RELATIVELY EASY.
I PREFER METHOD#1, AND SO WILL YOU!
6. METHOD#1=Referring to picture #2, screw the TPS adjustment screw one way or the other till the the cylinders are balanced. Open bypass screws to original position however many turns you wrote down. Wow, that was easy.
7. METHOD#2 Balance the Butterflies by first loosening the throttle body control rod lock nut, one on both sides. Then turn throttle body control rod adjuster, on vehicle left hand side, until cylinders are balanced. When finished, tighten the throttle body control rod lock nuts. Open bypass screws to original position however many turns you wrote down.
Now adjust engine idle speed as follows. Bring engine to prescribed temperature. *(158-176 degrees F or 70-80 degrees C) Adjust idle speed by means of the bypass air screws to1100 RPM +/- 50 RPM. Bypass screws should be usually within one half turn of each other. Do them a little at a time, first one, and then the other. I usually do them in one eighth turn increments. I keep the twin max hooked up for this too and use this to balance at idle. If you were getting a surging when holding the throttle position in one place in first gear while going really slow down the street it is because the throttle butterflies were out of synchronization right here about idle. I tell you, they are really sensitive.
*The Temperature specs are for the perfect person in a controlled environment. Such as using a large fan
Blowing on the engine to keep temperature down when at idle. I did use a laser temperature sensor just for fun to check it. Didnít really matter because it turned out perfect. I was soooo happy!
This ďbypassĒ air which is not controlled by the throttle butterflies is what is increased or decreased by the idle air bypass screws. Both idle speed adjustment and idle synchronization of the 2 throttle butterflies is accomplished with these screws. This adjustment have an effect at idle but once the throttle butterfly is opened by any significant amount the bypass air becomes insignificant.
Note: If satisfactory synchronization of the two throttle butterflies cannot be achieved at idle using the idle air bypass screws, then something else is wrong. There is an air leak. Valve adjustment may be incorrect. Significant differences in combustion chamber deposits may exist. All of these factors will effect synchronization at idle. However, go for a ride, see if you like the results, and if you do, the heck with everything else.