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[Thack]

Anyway, if we agree that it is nothing other than a fast idle device, I'm going to experiment with a gadget to automate it.



My plan is to tee across the temperature sensor, and automatically open the bi-starter when the temperature is below a certain level.



It's pointless, of course, but I like having something to mess about with. The most difficult bit will be finding a suitable way of motorising the bi-starter valve, so don't hold your breath!

[Thack]

Scalyback: yes, you need to hold it. Pulling and releasing it does nothing.

[Presto]

I don't think the bi-starter is a 'fast idle' devise. It supplies auxillary air for starting when the butterfly vavle is fully closed, as it should be for starting. Once the engine is started the bi-starter lever is released.

[Presto]

I should have said, once the engine has warmed up the bi-starter lever is released - like it says in the owner's manual!

[Thack]

Hi Presto: oh, yes, we agree. It's just a terminology thing. As you say, it provides more air, not more fuel, for cold starting. The ECU will provide the extra fuel.

[Michael]

By 'wedge' it on... I actually meant 'stick a wedge in it to keep it on'





Mine is springy too, if I should be saying such things in a public forum.

[Thack]

Mine used to be springy, but it's floppy now.

[Scalyback]

Well, Thack me, I'm glad we have sorted that one out!



I would like to thank Thack, Michael and Presto, for telling me how it works.



I just realised that I have never read the owners manual, except for running in. Nothing has ever gone wrong on Thunderbolt (My EFI WOODSMAN). Except of course for the very slow seep from the putty under the engine. (Thack, read http://www.hitchcocksmotorcycles.com/fo ... post_64404 See how I got done)

[Michael]

So, to get my head round this... it is like an air leak on a vacuum line on a car? ECU senses more air, so lobs in more fuel to compensate?

[Thack]

Michael, I think it's best to visualise it as a bypass around the throttle plate (which is supposed to be closed at tickover). It's rather like having the throttle cracked open a bit, in that it allows air to get to the engine. However, the ECU wants to know when the throttle is fully closed, because that's one of the times it goes "closed-loop" in order to keep the emissions low. That's why we don't adjust the tickover speed by altering the throttle plate - there's a risk that the "closed throttle" condition won't occur. Thus we leave the throttle plate alone - in the "I am closed" position, and admit air through a separate passage.



We've got two air bypasses round the throttle plate: the first has a screw adjuster in it and sets the idle speed by altering the amount of air that can get through. The second - the bi-starter - can be opened temporarily to allow a higher air flow while the engine is starting.



By monitoring the air pressure sensor in the inlet manifold the ECU knows how much air is getting through those two bypasses and injects the right amount of petrol for the ideal mixture. When the engine is cold (using the temperature sensor) it injects more, so the mixture is a bit richer. Once the lambda sensor is up to temperature and working properly, the ECU uses the feedback from the lambda sensor to set the mixture just right (this is known as closed-loop running).



Does that help at all?