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[Thack]

Colleagues,



There seems to be some confusion about this bi-starter thing on our left handlebar. Some people reckon it makes the mixture richer. Others say it simply increases the air flow to provide a fast idle.



As I see it, the mixture is controlled solely by the "on" time of the injector, and therefore is decided by the ECU. A cable-operated valve on the throttle body can't possibly affect that, can it? If I wanted to give the rider a manual way of richening the mixture, I'd just use an electrical switch to signal the ECU.

In any case - that's what the engine temperature sensor is for: to let the ECU know when the engine is cold and needs a richer mixture.

Having looked at the throttle body/injector assembly, it appears there is no way the ECU can control the throttle opening - there is no actuator on it. It means there is no ECU-controlled fast idle when cold. This must surely be one of the few motorcycles on the planet that has such a crude system. So my conclusion is that the bi-starter is solely a manually-controlled fast idle.



So, two questions: firstly, does anyone know better? The above is just speculation. Secondly, why is it called "bi-starter"? "Bi-" normally means two. Two what?

[Les]

My manual says it is to control a spring loaded piston in the throttle body adding extra fuel to make the mixture richer personally I have no idea but it works

[Thack]

Thanks for replying, Les. I'm wondering where the extra fuel comes from.

[Presto]

A lambda sensor only begins to work effectively when it has reached its working temperature, approx 300°c. If the sensor does not reach this ‘working’ temperature no signal will be sent to the ECU. When no signal is received from the sensor, as when an engine is first started from cold or when the sensor or connection fails, the engine control system sets a fixed rich-fuel mixture. (This is referred to as ‘open loop’ operation.) If the engine fails, for whatever reason, to go into ‘closed loop’ operation the fuel mixture will continue to be too rich for efficient running.

The ‘bi-starter’ is a cold start system used in fuel injected engines. In the EFi engines it relies on a cable-operated valve. The valve controls an internal passageway, either opening or closing this channel. When the bi-starter is opened extra fuel is fed to the engine, creating the rich fuel/air mixture needed for easy starting.

In some cases the standard cable does not have sufficient ‘free cable’ length to allow the bi-starter channel to open fully. Consequently the fuel mixture is too weak for easy starting.

But the equal and opposite effect of lack of ‘free cable’ is that the bi-starter never fully closes the bi-starter channel. Consequently the fuel mixture is always too rich for normal running. This extra richness of fuel seems to by-pass the engine management system. The rich mixture results in poor economy, excessive carbon build-up in the combustion chamber and exhaust, and spark plug failure.

[Thack]

Presto, let me ask you the specific point: the passageway that is opened by the bi-starter valve - where does the extra fuel

[Thack]

Oh, damn - sorry.........

Presto, let me ask you the specific point: the passageway that is opened by the bi-starter valve - where does the extra fuel come from? The bi-starter valve is in the throttle body, whereas the fuel goes only to the injector.



From what I can see by inspecting the exterior, the bi-starter passageway seems to open an extra air path (it appears to run alongside the adjustable idle air passageway). So it looks more like a fast idle device rather than a fuel enrichment device.



In any case, why would you need a manual enrichment device for cold starting when the ECU could do that itself?



Have I misunderstood?

[Michael]

Thack... the bistarter is a fuel mixture enricher. Wedge it on, go for a ride, pull the plug and you will see.




BTW if the cable isn't seated properly, which can easily happen as it only is just long enough (so can pop out of its seat in the throttle body top), then you will run rich and kill plugs quickly, as Presto says.




Why doesn't the ECU compensate... as Presto also says, it doesn't have a sensor to do so when operating cold and open loop. There are two options, 'blind' ECU enrichment for the first few minutes until the engine is warm and then go closed loop, or manual enrichment as and when needed. Summer, and most autumn and spring riding does not need a richer mixture to start, even up here in cold and wet Scotland. In the depths of winter, aye, a wee bit extra fuel helps but only for 5 or 10 seconds normally.

[Scalyback]

mine is springy.



I assumed you just operated it, let it go and started. If I need it, then do I have to hold the lever operated until the engine cheers up?

[Presto]

Apologies! Thack is correct. The bi-starter opens an auxiliary air supply for starting – not extra fuel. The method is that cold staring should be with the throttle closed, the butterfly valve fully closed. The bi-starter cable opens a valve that opens an AIR passage, to supply an appropriate amount of air to correspond with the full fuel supplied by the injector at its open-loop, full fuel supply, stage.

[Thack]

Thanks, Presto, I thought that was the case. Michael, it does look as if the bi-starter has no way of adding any extra fuel - it can only be an "extra air" device.