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[Thack]

Presto writes: "Second thoughts, if all the 'bi-start' does is allow extra air why not simply open the throttle slightly? Also would not the 'extra' fuel be cancelled-out by the 'extra' air and the mixture end up being 'normal', rather than richer?"



Correct - it's exactly the same as opening the throttle slightly. (Actually, to be strictly correct its exactly the same as unscrewing the idle speed screw a bit, because the bi-starter does not affect the TPS voltage.)



As I mentioned earlier, the bi-starter has NOTHING TO DO WITH COLD START ENRICHMENT. You are exactly right: the extra air results in extra fuel so the mixture ends up as normal. The enrichment occurs when the ECU detects a low engine temperature (the temp sensor is on the back of the barrel).



I repeat: the bi-starter does EXACTLY the same thing as opening the air screw by about three quarters of a turn. No more, no less. It is NOT the FI version of a choke.



So, Presto, your understanding is absolutely correct but your expectations are not! The bi-starter is JUST A FAST IDLE DEVICE.



Personally I think it's a piece of crap because you can't even jam the lever open to let the engine fast idle while you put your gloves on. And it takes almost no skill at all to crack the throttle just a tiny amount, to have the same effect as the bi-starter.



All decent modern systems (i.e. on pretty well all Japanese bikes) have an electronically controlled actuator to raise the idle speed automatically without user intervention. Using that simple manual "bi-starter" saves RE a significant amount of money over the more complex and expensive actuator-based system.

[Thack]

I forgot to add that I've ditched the bi-starter on mine and added my own electronically-controlled actuator, much like a Japanese bike. You can see a photo of it here:







Let me emphasise that this is very much a prototype - primarily to explore the feasibility of such a system. The finished version will look nothing like this, and will probably operate on the air screw rather than by providing a moving throttle stop.



The primary role of this device is as a temperature-controlled fast idle device. It's a great improvement on the bi-starter, because it's automatic, and the amount of speed boost depends on how cold the engine is.



After getting it working I added an anti-stall function to it. When the engine is fully warmed up, if the idle falls below 700rpm it blips the throttle to avoid it stalling.



In this video I've deliberately turned the idle speed too slow so that the "blipper" kicks in continuously, thus allowing me to observe its action. In normal use it doesn't keep "hunting" like this, but only kicks in when the idle speed drops too low (which it is prone to do on our UCE bikes).

YouTube

[Thack]

Ooops - sorry, you've gotta click on the link that says "YouTube". Could have made it clearer!

[Les]

I like the servo Thack you must be a model maker

[Thack]

Hi Les,



Not really! I've seen these servos used in model RC aircraft and boats, so I thought I'd buy one to experiment with. Quite useful, actually.

[Michael]

Are you going to start supplying those to othe rneedy EFI owners?!! Basically, how much!!!???

[Thack]

Hi Michael,



I haven't really thought about that, and I would need to come up with a better solution, I think. But I promise I will think about it!



Meanwhile, I should point out that it's a bit of a bodge - the best solution is to fix the cause rather than the effect, which I THINK is to do with an excessively rich mixture at idle and sub-idle speeds. Thus I want to see if I can find an easy solution for that, instead, which may well eliminate the need for an anti-stall device.



Having said that, the cold start fast idle function is great, MILES better than that stupid bi-starter because it's fully automatic. So even if I fix the idle mixture, I will still want to keep something like this for the fast idle.



I promise to report back.