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Hi All,
I have been reading a lot of info on this subject in this forum (both technical and informative) but still haven't quite grasped what AI actually does and what you gain by removing it with regards to a EFI
Thruxton.
Any plain english explanation would be most appreciated.

Thanks. :confused:
 

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I think what it does is burn up any bits of fuel escaping through the exhaust - an anti-pollution device. Don't know about the EFI stuff though, but what I've gathered so far is the AI system is factored into the electronic readings of engine operations that go to the computer [?] of the machine. Have not yet sorted it out. Pipe bluing and engine temperature seem to be the leading reason for removing it on carburetted models, along with a nicer look and spark plug accessability. The pipes on my EFI Thruxton are in good shape at almost 1,200 miles - blue just near the head connection. My Bonneville's pipes, however, blued up down to the crossover with only a few hundred miles on the bike.
 

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The injection of air into the exhaust ports allows any unburnt fuel to burn in the exhaust thus cleaning up the exhaust gases of unburt hydrocarbons before they exit into the atmosphere.
I've been told not to remove it on EFI models. Why? I don't know. I guess it may be something to do with how the O2 sensors read the exhaust gases.
 

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Sorry to say this but above two posters are a bit misguided.... common myths repeated which become accepted half truths when discussing AI on EFI bikes.
I just removed AI from my EFI Bonny. I will post a DIY in the next few days so if interested, have a look for it.
Cheers,
George
PS: I have discussed some of the nuances in multiple threads and yet members here still don't quite grasp it...some do, but many others don't and why I am not going to wax further as to why removing AI on an EFI bike is viable. I will capture some of this in a dedicated AI removal on EFI bike DIY thread.
 

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Sorry to say this but above two posters are a bit misguided.... common myths repeated which become accepted half truths when discussing AI on EFI bikes.
I just removed AI from my EFI Bonny. I will post a DIY in the next few days so if interested, have a look for it.
Cheers,
George
PS: I have discussed some of the nuances in multiple threads and yet members here still don't quite grasp it...some do, but many others don't and why I am not going to wax further as to why removing AI on an EFI bike is viable. I will capture some of this in a dedicated AI removal on EFI bike DIY thread.
Well why don't you simply "wax" accuracy and spill the beans about the AI system and an efi motorcycle?
 

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Well why don't you simply "wax" accuracy and spill the beans about the AI system and an efi motorcycle?
That sounds like a reasonable request from someone wanting to understand how the function of the AI is different on a carbureted bike vs its function on a EFI bike. I'm personally not interested in learning how to remove the system, since I will probably never own an EFI Bonnie, but a short explanation of how the AI's purpose is different on carb'd vs EFI bikes would be an interesting topic.

If you've already posted a thread that provides this info, could you provide the link?

Thanks,

Bob
 

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Purpose is the same Bob. TPS senses throttle position. As throttle closes, TPS tells ECM...ECM tells solenoid to open AI valve. Engine vacuum is maximum at throttle closure and therefore air is sucked, i.e. drawn/injected into annex exhaust chamber connected to exhaust port. Extra air is injected into pipes at combustable ratio with fuel dumped into pipes unspent from combustion upon throttle closure. Combination of air and fuel burns fuel outside of combustion chambers inside of hot pipes which act as heat source for post combustion that would typically just dump fuel into the environment without an A/F ratio conducive to burning...what happens without AI...less environmentally friendly. AI has very little to do with O2 sensor function as AI is only operative whan the throttle is closed.
Hope that helps,
George
 

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What benefit do you get by removing it?
A reduction in exhaust pipe temperature and therefore less discolouration, reduction or elimination of popping noises in the exhaust and, some insist, that the constant blasting with gusts of cold air doesn't do the exhaust valves any favours.

I'd like to ask George if there is any sort of simple oxidation catalyser on the Bonnies pipes or silencer. All my modern bikes combine a SAI (secondary air injection) with one of those. The idea is that the excess unburned hidrocarbons are burned with the extra air and the catalyser turns the resulting CO into CO2.

Here's one inside a silencer:



And another stuffed into the downpipe itself:

 

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A very good question Forchetto and I don't know the answer with any certainty. Norman Hyde who knows a fair amount about these bikes suggests the '09 EFI bikes...EFI began in '08 in Europe...all have catalysts in the header pipes...likely a honeycomb config. as you show. I know of nobody that dissected the new pipes. I believe they are fractionally larger OD which has led some to believe...further speculation...that they are double walled. I would wager a fair amount that the EFI headers an not doubled walled. Perhaps the most telling element of whether the new bike headers have catalysts is the color they turn. Heat transfer appears to be quite different. They don't blue in the traditional sense of carbed bikes but turn a more straw color. This maybe due to fueling difference between EFI and carbs but the root cause maybe in fact of what you suspect and what Norman Hyde believes and that is the new headers do have catalysts. This does beg of course the larger issue...what would the net affect of eliminating AI be with cats inside the headers? Again...no data on this. We are all learning together about the newish EFI bikes. My position is...if the cats don't like a bit extra unburnt fuel spilled inside them by disabling AI, then I will have to ream the cats out. :p
Cheers,
George
 

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Thanks for replying George. I'm still waiting for my bike, but as soon as I get it I'll have a look inside the pipes. I have a Borescope, this is the sort of tool proctologists use to look up people's bottoms :) .It comes with a 34" iluminated fibre optic probe that should reach right inside, (the pipe I mean...).

If it has then the AI removal might damage the catalyser. They need the extra temperature to work properly.
 

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George - Thanks for your previous explanation to my question.

You make a good point about cat converters not liking any extra raw fuel hitting them. Although this is an exaggerated example, back in the day, I drove a 1976 Ford station wagon company car (pretty exciting, huh?).

I got stranded in the 'blizzard of '78' in Findlay, Ohio, and was holed up in a motel for nearly five days before the State Police would allow any travel other than emergency vehicles.

I really wanted to get back to my girl friend, who was several hundred miles away, so, once the roads were opened, off I went. Then, the Ford began missing off and on .... maybe a bad plug. Well, I didn't have time to stop and worry about the V8 running on 7 cylinders, so on I went.

Until I hit the W Va Turnpike. That's when I noticed what I initially thought was the sunset coming thru the rear window ..... until I saw flames in the rear view mirror! Rear seat was on fire. The cat converter, mounted under the car, had gotten so hot from burning raw fuel, it caught the seat on fire through the floorboard. Fortunately (or unfortunately .... I hated this car)....., a State cop I knew pulled in, grabbed a fire extinguisher, and put it out.

Bob
 

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Wonder if EFI Bonnies do a fuel shut-off when coasting?

Just happened to think of this. My first BMW, a 1985 K100RS 'flopped over 4' with Bosch FI, used a microswitch to signal the fuel injection computer to shut off the injectors when the throttle was closed at speed. Fuel was shut off until the engine speed dropped to 2000rpm, at which point the injectors once again were allowed to spritz fuel. You could actually feel a slight 'bump' as they came back into play. I think BMW used this method of keeping excess fuel out of the exhaust for several years, but don't recall if my 1999 K bike, with Motronic ECU, used the same system. The first K's had no cat converters. Later ones did.

Bob
 

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Ther are no cats in the headers of US spec 2009 EFI Bonnevilles - I've personally run a 1" chain from the cylinder head end to the muffler end on my bike.

Dick
 

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A reduction in exhaust pipe temperature and therefore less discolouration, reduction or elimination of popping noises in the exhaust and, some insist, that the constant blasting with gusts of cold air doesn't do the exhaust valves any favours.

I'd like to ask George if there is any sort of simple oxidation catalyser on the Bonnies pipes or silencer. All my modern bikes combine a SAI (secondary air injection) with one of those. The idea is that the excess unburned hidrocarbons are burned with the extra air and the catalyser turns the resulting CO into CO2.

Here's one inside a silencer:



And another stuffed into the downpipe itself:

That looks almost exactly like a BMW cat!

Jim :cool:
 

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Ohio...have to say what you wrote was on my mind after I buttoned up my EFI bike last night after removing AI and firing it up. Dick...the 50 ohm resistor worked fine...no CEL. Forchetto's pictures resonated with my conversation with Norman Hyde about EFI bonny headers having cats and I was visualizing the scenario that Ohio described about raw fuel running out of the exhaust ports down header pipes into white hot cats...lol.

Forchetto...welcome to the board btw. I can tell by your comments you are a smart motorhead and your contribution here will be valued. Good luck with your new Thruxton...you will love it. I hope you do check your tubes on your European spec bike...a good time is when you replace the stock silencers which you inevitably will....by fishing your electronic probe from rear to front thereby not having to unhook the headers at the jugs. Btw...please send that electronic snake with an eye to me if you would as I am over 50 years old and would like to check my personal plumbing. ;)

Dick...thank you for setting the record straight about running a chain up the headers on a stateside bike. I feel a whole lot better knowing that raw fuel will not be dumped onto cats inside the header pipes. This has turned out to be another great thread as we learn together about EFI.

As mentioned...I will put the DIY out there shortly for removing AI on an EFI bike. I would have tested it last night but it was raining and I would like to ride the bike before I do the write up to determine if AI has mitigated some of the light popping with the stock factory map.
Cheers,
George
 

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as far as i am aware on the speedmaster at least the cat is in the pipes not the headers, and the TOR do not have them in at all. :)


also intresting think on AI beliw with a cat, not what you may think,

Theory and origins

Secondary air injection (commonly air injection, colloquially smog pump, trademark Air Injection Reactor) is an automobile emissions control strategy introduced in 1966, wherein fresh air is injected into the exhaust stream. The exact mechanism by which exhaust emissions are controlled depends on the method of injection and the point at which air enters the exhaust system. The first systems injected air very close to the engine, either in the cylinder head's exhaust ports or in the exhaust manifold. These systems provided oxygen to oxidize (burn) unburned and partially-burned fuel in the exhaust before its ejection from the tailpipe. There was significant such unburned and partially-burned fuel in the exhaust of 1960s and early 1970s vehicles, and so secondary air injection significantly reduced tailpipe emissions. However, the extra heat of recombustion, particularly with an excessively rich exhaust caused by misfiring or a maladjusted carburetor, tended to damage exhaust valves and could even be seen to cause the exhaust manifold to incandesce.
[edit]Changing function

As emission control strategies grew more sophisticated and effective, the amount of unburned and partially-burned fuel in the exhaust stream shrank, and particularly when the catalytic converter was introduced, the function of secondary air injection shifted. Rather than being a primary emission control device, the secondary air injection system was adapted to support the efficient function of the catalytic converter. The original air injection point became known as the upstream injection point. When the engine is cold, air injected at this point cleans up the extra-rich exhaust and raises the temperature of the exhaust so as to bring the catalytic converter to operating temperature quickly. Once the engine is warm, air is injected to the downstream location — the catalytic converter itself — to assist with catalysis of unburned hydrocarbons and carbon monoxide.
 

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There are many different executions of AI or SAI. What is unknowable on our bikes is when the ECM algorithm energizes the solenoid and/or whether or not during this time the O2 sensors go into open loop or default to a particular voltage i.e. A/F ratio per given throttle aperature. The temp sensor maybe in the mix for supplementing cool air at start up as well...again to reduce emissions.

Your comments about the cats being inside the silencers versus the headers is what I believe to be true on US spec bikes at least. I suspect...unconfirmed...that the original silencers on my T100 had cats. They were as heavy as boat anchors. The TORS I replaced them with do not of course which makes removing AI a bit less vexing. One sidebar on removing AI when I fired up my bike last night after reinstalling the gas tank. The bark at idle and above on my TORS sounds louder. It maybe imagined or perhaps the TORS are waking up a bit as reported. Perhaps some of the raw unspent fuel will help ravage the stuffing in the TORS to make the bike sound even better. :)
Cheers,
George
 
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