749 Air mix adjustment I adjusted the air mix screws on my 749 and discovered that the front cylinder mix screw has no discernible affect on the idling of the bike. The bike stalled when the rear screw was turn in fully. Can someone answer the following; I read somewhere that the ignition system may atomically compensate for mix on the front cylinder - is this correct? Where is the air inlet for the mix circuit on the front throttle body? From pictures on the web it looks like it may be on the front of the throttle body at the mixture screw (see pic). Any suggestions why adjusting the mix screw on the front cylinder has no impact. Thanks in advance. Steventh
I'm a little confused as to what you are trying to achieve. On your bike the air/fuel ratio is adjusted via the diagnostic sytem using fuel trimming. Best idle is achieved through the fuel trimmer. The adjusters on the throttle bodies are used for balancing the throttle bodies. The ECU has maps to balance the horizontal and vertical cylinders. These tend to be referred to as Delta Maps. When I tuned my 1198 using an Innovate AFR I had to take readings for both the horizontal and vertical cylinders so that my tuner could create the delta mapping.
Chrisw, I want to make a minor adjustment to the idle mix to get rid of the occasional stalling when stopped. What you say is correct. In addition to the ECU the throttle Bodies have an air mix screw which changes the fuel ratio and to a limited extent the vacuum at idle. Their is also a "trim" screw on the front throttle body linkage that adjusts the relative position of the front butterfly.
Do not change idle on 749. What you describe is known issue, especially on S models. If all is perfect with bike get someone to adjust timing for you and it will stop, check valve clearances as well. Raising idle is just masking the problem.
The air screws serve two functions... As mentioned they are used for balance, but also for idle speed. Screwing them out bleeds more in and increases isle speed. The CO readings are then tweaked with software. None of the screws on the throttle housing should be touched. They are fixed with yello tamperproof paint. if you're suffering idle issues, try and get a reset on the TPS first, then set the throttles up. Unless you can access to a exhaust analyser then you'll struggle to get it just right.
Folks, Thanks for your advice. The "right" way of tuning the bike is to get the workshop to do it. Fiddling with the screws (access from the right side of the airbox) can get you into a whole lot of pain. If you count the number of rotations from the seated position the screws have been set by the factory you can always return the air mix screws to their original position. Changing the mix screws will change the idle and if you are comfortable with playing with the bike (and have recorded the starting position to revert to if it goes pear shape) may lead to an improvement. I will answer my own questions in case someone reads this post in the future. I read somewhere that the ignition system may atomically compensate for mix on the front cylinder - is this correct? - No its not. Where is the air inlet for the mix circuit on the front throttle body? From pictures on the web it looks like it may be on the front of the throttle body at the mixture screw (see pic)? It appears this is the case Any suggestions why adjusting the mix screw on the front cylinder has no affect? Changing it changed the vacuum but did not make an audible difference to the revs on my bike. PS - this pic was taken from the web
That's clearer. If you want to do home maintenace to address your issues you need to put some kit together For diagnostic, everything you need is here http://ducatiforum.co.uk/f41/free-diagnostic-software-14914/ A Gunsons Gas Analyser is good for setting the fuel trim. I use one of these to take the reading from the header pipes (size 1/8) BSP TAPER THREAD x HOSE TAIL END CONNECTOR FITTING brass air water fuel bspt | eBay Some have had success setting the fuel trim using trial and error. JPDiag allows you to TEST the setting before storing it. Using this method you can get the best high idle through the fuel trim. For balancing the throttle bodies you need a carb balancer or you can make a manometer using some drink bottles or clear hose. There are details of 'how to' on Youtube.
