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I sat on a '09 Bonnie today with the alloy wheels. In the speedo head there are two lights, one with an engine symbol and one with a fuel tank symbol.

So, there's a check engine light. Damn. I am so sick of looking at illuminated check engine lights on my cars that I dread the same on a Bonnie. But, with all the tech heads around here I am sure there will be many posts on how to disable the darn thing, in addition to cover-it-with-electrical-tape method. Or maybe the thing is actually important? Seems those usually indicate some emissions problem, but as we all yank the AI anyways what's the point?

And how does a low fuel light even work? With all the sloshing of fuel back and forth in the tank (when the bike is properly ridden), how does the sensor know if you're low or not? Or does it just light up when the injectors are fuel starved and indicate "you just ran out of fuel" instead of "you're gonna run out in a while"?

Any insight will be appreciated and enjoyed. But first in closing, I sat on the bike at Moto Primo south of Minneapolis which has all sorts of brands of bikes. Whether you prefer spokes or alloy, both flavors of Bonnie out-cooled about every other bike there.
 

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BB - I can't believe you are bumping a 10 year old post, neither can I believe that you had no replies to your queries. Still I will try to provide some answers for you.
Regarding the engine light, I know you've always been a carb guy, but the light, along with a cheap OBDII scanner can actually give you some good information and by alerting you, save you loads of money in repairs. The light does indicate emission problems but also can give you a heads up on things such as open/short crank position sensor, bad fuel injectors and ignition components. So its a pretty important early warning to have. Generic OBD DTC's (Diagnostic Trouble Codes) follow a standard, consisting of a 5 character code and depending on the scanner you are using, it will decrypt the DTC for you, some scanners include a more detailed description of the fault. There are also manufacturer specific DTC's and lists of those and generic ones can be found online. The air cooled EFI system is pretty basic though so you can usually get by with generic DTC's. The emission things you mention such as SAI and O2 sensors can be 'switched off' with suitable software that connects to the ECU such as TuneECU. These things are not in fact switched off, but prevented from producing a DTC and lighting up the light. For the light to come on in the first place a DTC has to be generated in the ECU memory, but also note that it comes on with ignition whilst the fuel pump primes before the engine start. This article will show you what the 5 character DTC's mean:


The Low Fuel light is the EFI version of the 'reserve' position of the petcock. Personally I prefer the reserve petcock function but due to a pump residing in the fuel tank, and the fuel being sent directly to the injectors under pressure at 46psi its not really feasible. But, its better than nothing and does have a couple of advantages over the petcock - firstly, your engine doesn't just suddenly die in the fast lane of the freeway, and secondly you don't have to fiddle about under the tank with one hand while your bike is coming to a quick halt. Here's how it works:
Attached to the pump assembly inside the tank is an electrical component called a thermistor. This changes its resistance as its temperature changes. With a full tank the thermistor is totally submerged and kept cool by the fuel, so its resistance is high and that keeps the light off. When the fuel level in the tank drops and exposes the thermistor it begins to heat up since it has lost the cooling effect of the fuel, its resistance falls and the light comes on. If the fuel is sloshing around this doesn't have a great effect since it takes time for the thermistor to warm or cool. What does have an effect is the gradients you are riding on - in hilly country this will make the light periodically come on and go off for a short while, until the fuel level falls a bit lower. In my experience this only happens over a few miles. When the light first comes on there should be a 40 mile reserve to look for the nearest filling station.
 

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BB - I can't believe you are bumping a 10 year old post, neither can I believe that you had no replies to your queries. Still I will try to provide some answers for you.
Regarding the engine light, I know you've always been a carb guy, but the light, along with a cheap OBDII scanner can actually give you some good information and by alerting you, save you loads of money in repairs. The light does indicate emission problems but also can give you a heads up on things such as open/short crank position sensor, bad fuel injectors and ignition components. So its a pretty important early warning to have. Generic OBD DTC's (Diagnostic Trouble Codes) follow a standard, consisting of a 5 character code and depending on the scanner you are using, it will decrypt the DTC for you, some scanners include a more detailed description of the fault. There are also manufacturer specific DTC's and lists of those and generic ones can be found online. The air cooled EFI system is pretty basic though so you can usually get by with generic DTC's. The emission things you mention such as SAI and O2 sensors can be 'switched off' with suitable software that connects to the ECU such as TuneECU. These things are not in fact switched off, but prevented from producing a DTC and lighting up the light. For the light to come on in the first place a DTC has to be generated in the ECU memory, but also note that it comes on with ignition whilst the fuel pump primes before the engine start. This article will show you what the 5 character DTC's mean:


The Low Fuel light is the EFI version of the 'reserve' position of the petcock. Personally I prefer the reserve petcock function but due to a pump residing in the fuel tank, and the fuel being sent directly to the injectors under pressure at 46psi its not really feasible. But, its better than nothing and does have a couple of advantages over the petcock - firstly, your engine doesn't just suddenly die in the fast lane of the freeway, and secondly you don't have to fiddle about under the tank with one hand while your bike is coming to a quick halt. Here's how it works:
Attached to the pump assembly inside the tank is an electrical component called a thermistor. This changes its resistance as its temperature changes. With a full tank the thermistor is totally submerged and kept cool by the fuel, so its resistance is high and that keeps the light off. When the fuel level in the tank drops and exposes the thermistor it begins to heat up since it has lost the cooling effect of the fuel, its resistance falls and the light comes on. If the fuel is sloshing around this doesn't have a great effect since it takes time for the thermistor to warm or cool. What does have an effect is the gradients you are riding on - in hilly country this will make the light periodically come on and go off for a short while, until the fuel level falls a bit lower. In my experience this only happens over a few miles. When the light first comes on there should be a 40 mile reserve to look for the nearest filling station.

great information and clearly presented, thanks
 

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Ah, thanks so much Ripper. You're a good man, I didn't want to wait another 10 years for an answer :)

As it turns out we bought a 2009 for wife. She doesn't put on very many miles, and she does not allow me to tinker with it other than maintenance. But the engine light has stayed off. I got an ODBC cable to read the codes from my PC, but I don't believe I've ever hooked it up. The thing just runs without worry.

With her bike unmolested, her not weighing much and her steady throttle hand, she gets amazing gas mileage will up into the 50s and maybe into the 60s. I'm down in the mid 40s, and she pretty much always rides with me, so not sure her fuel light has come one very often. It has a trip odometer we reset at every stop, and that's what we rely on. But the light can't hurt. I always wondered how the sensor worked, thanks for that.

I was really drawn to the simplicity and low-tech nature of my carbed Bonnie. I was actually put off by these new fangled lights and those injectors, but it has turned out to be a non-issue. It's an awesome bike to be sure, despite all that ;)
 

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I was really drawn to the simplicity and low-tech nature of my carbed Bonnie. I was actually put off by these new fangled lights and those injectors, but it has turned out to be a non-issue. It's an awesome bike to be sure, despite all that ;)
IMO BB, they are all awesome regardless of how fangled they are. :)
I think its human nature to dislike that which we do not know or are not familiar with but personally I had a curiosity which overrode all that. I'm the kind of person who, as a kid, would have all my toys stripped down to their component parts by boxing day (especially if they had batteries). My parents always scolded me as destructive, never realizing the wealth of knowledge I was acquiring.
I don't like these emission controls either, but its now law here, and probably on your side of the pond too. Its that which has forced manufacturers to take to things like EFI and liquid cooling, so rather than take an instant prejudice I decided to learn what I could about it, and along the way I have found all the advantages of EFI - in short, more reliable starting and running due to the myriad of sensors - their goal, from a manufacturing perspective is to keep a firm control on emissions, yet somehow they make life easier when it comes to things like tuning or servicing. For example, those injectors are not encumbered by shims or air screws, the mixture is set simply by how long they are open at a given throttle opening, and that is a simple adjustment on a computer screen. The TuneECU software gives you the ability to do things more quickly and with greater precision, such as balancing throttle bodies or adjusting the rev limit, or zeroing the throttle position sensor. Carbs, however much we like them - and like you, I grew up with them - are not coming back. If I were to think of any disadvantage to EFI, I would say poor reliability of cheaply made sensors. The electrical systems on these bikes was never that good from the beginning, including the wiring itself but that is down to the manufacturer's bean counters.
Regarding the OBD codes, you don't need anything fancy to read or delete them (TuneECU also does that), just a cheap hand held reader for any car will do to get the fault code, then you can google the code to find out what it means.
 
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