pilot air screws. strange but true!!!

[jerry]

I recently did a full service on my M750 everything ,shims,oil, filters etc etc carb rebalance
she is running really sweet , set the pilot airscrews at 21/2 turns out but after riding a bit i thought she was a bit over rich at tickover and hesitant off the line , so i turned the pilot air screws out to 3 1/2-4 turns and wow she is much crisper off the line and tickover and starting are better as expected ..........but what I did not expect was the better midrange and top end response ????? those settings should not have an effect above 2000 rpm but the do and I noticed the same thing on my 750ss as well.

Today i set the carbs up on a friends M900 and same thing happened when we test rode it ....its not subjective its a noticable before and after effect and can be reversed .

anyone else had this effect or a scientific explanation ???

[Saint aka ML]

I guess out on stock crabs means more air so leaner running? Same happened on my fcr mainly as now plugs were not getting wet at low rpm so throttle response was more instant.

[Dookbob]

I,m going to have to try that

[Sirc]

The idle mixture screws on our standard 38 Mikunis adjust the fuel Jerry and you have enrichened the mixture at idle upwards not weakened it. Considering the time of year/temperature it makes perfect sense. I once had a Porsche engined Seat Ibiza with a carb that was sensitive to temperature and it took me a year to realise but from then on I weakened it come Spring and enrichened come Autumn, about 1/4 to 1/2 a turn is all it needed. I am new to my M900 and it started to idle/pick up poorly last week and cleaning gapping plugs made little difference. I have just turned my mixture screws out (anticlock) about 1/4 turn out to see if it will cure the problem. Generally if idle mixture screw is situated between butterfly and air filter it will meter air and if between butterfly and engine then it's metering fuel.

[utopia]

I dunno what truth there is in it (though I suspect there may be quite a lot), but I've heard that manufacturers often set pilot mixture settings on the lean side in order to improve emissions at lower engine speeds.
Anyone else heard this ?

[Sirc]

totally true Utopia - right across the board cars/bikes and the professional Ducati specialists on here will be able to add more. A lot of the irritating hesitation problems that occur on laterinjected/ECU bikes is down to the 'only just rich enough' approach that manufacturers are forced to adapt to meet the more and more stringent emission regs. It means that if a slightly aged bike isn't in tip-top tune and condition then the predetermined mixture setting will 'get you'. I can understand why people resort to power commanders and 'tunable chips' but we shouldn't have to. Most of the above can be overcome crudely on most bikes by acting on an adjuster in the ECU (as i'm sure you are aware) but this will in turn leave the top end richer than ideal (which is what most owners who decide to take this route end up with).