Ducati Sporting Club UK > Model Specific - Discussion, Technical Problems and Help > 998 / 996 / 916 / 748 > Fast idle button

[Lee1980]

I have a 748s with the little click on fast idle button and I always use mine in the morning.

After 8-9 hours at work the bike is uncovered outside it starts without the fast idle button, no hesitation just fires up first press. Even though the weather is getting very cold.

My main question is, is it best not to use it if you can help it as it revs at 2000rpm when this is on. I usually knock it off as soon as i can and ticks over fine.

I presume it doesn't work the same as a choke on a carbed bike.

Whats the best starting procedure?

Thanks

Lee1980

[Shazaam!]

The fast idle button just opens the throttle as if you were twisting the throttle a-little yourself.

Avoid using it.

If you need to give it extra throttle for a moment in cold weather to prevent stalling, do it manually. Running a superbike at the higher fast-idle RPM is a very bad idea because measurements have shown that it takes as long as 90 seconds for oil to reach the vertical cylinder rocker arms and camshafts. So you're running on a surface film of oil that's left over from your last run until the sump oil reaches the cams. So it's best to wait for this to happen at as low an engine speed as possible.

[Lee1980]

I will try it in the morning with out it as well. Does the bikes cpu know it is cold and adjust according to the temperature?

Thanks

Lee1980

[Shazaam!]

Yes, Ducati's fuel injection CPU has a coolant temperature sensor and an air temperature sensor.

Engines need more fuel when for a cold start as there is no heat in the ports and chambers to keep the fuel atomized as vapor, so it condenses. Fuel as a liquid burns very badly in the combustion chamber, so throwing more at it ensures enough stays as vapor for some sort of combustion. Injected engines get a very nice fuel spray from the injectors and this is why injected engines behave better when cold.

A coolant temperature sensor is used so that the computer can add additional fuel to its fuel map while the engine is warming up, and also to retard ignition timing when the engine gets too hot. The computer stops enriching due to low temperature at between 80 and 90°C. So at least from a fuel correction standpoint, the proper operating temperatures for a fuel injected Ducati is above these temperatures.

Further, on a cold morning the air is denser so an air temperature sensor will prompt the CPU to add fuel to its 20°C ambient fuel map to compensate. If the day is hotter than 20°, it reduces fuel.

[Lee1980]

Shazaam you must know everything there is to know about bikes.

Thanks

Lee1980

[Shazaam!]

Thank you Lee. I look forward to your future postings.

And to all the others here who have made a public thanks for my comments or help, a thank you to you as well. But isn't that why we're all here, to help each other and learn? I feel I learn just as much as you do from my attempts at being helpful or informative.

Please, keep in mind that I didn't invent the answers. They were given to me somehow or I found them somewhere along the way, sometimes in pieces. But in any event, they're is not mine to keep ... so I share them.

Sure, it takes some effort on my part, but I don't consider that a burden, it's really a pleasure to be able to help others who have the same interests. In all honesty, I have learned a great deal from many DSC members in this forum, who have proven, time and again, that it is all of us in combination that makes this place work. Some give a big piece, some a small, some offer an anecdote that along with others reveal a pattern to a problem. But who's to say which small piece will be the keystone. All of our pieces together make a bridge to understanding.

Shazaam!

[TopiToo]

Hello Shazaam,

After your last comments I would have no problems putting you forward as Honorary President. Unfortunalty I have no power. . .

Another page to my "Shazaam Workshop manual"

regards

TopiToo

[rockhopper]

There is an argument that says that at low revs the loads on components such as cam lobes is increased compared to running them at higher revs.
Can't remember why this should be right now though.

[Ant]

Thats correct rockhopper,when you first fit a new cam you have to run it in at 2000rpm straight away and not let it idle

[nelly]

You can adjust the fast idle speed by adjusting the slack in the throttle cable with the adjuster on the throttle housing. Less slack will increase it, more will reduce it.
Mine runs at about 1200rpm on the button, not a lot above tickover but just enough to let it start.
I've found that if the fuelling is set up correctly, it won't usually start from cold without the button. Especially in our climate. If it does, then it's probably a little rich??