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[ric]

Thack, unfortunately I can't give you what you're asking but will add a little something purely for amusement value.



The Triumph EFI Twins like the Enfield have a less than comprehensive Keihin system. The Triumph set-up will have the engine running rich enough to create large sooty deposits in the exhaust pipe if the removable rubber cap used to seal the Manometer stub either developed a split or was not fully replaced after balancing the injector bodies. In these circumstances the TPS value remains low/unchanged but an artificially lower than expected MAP value is introduced.



I haven't any OEM Triumph fuel maps to hand to check, only other peoples along with my own collection but at tick-over speeds the non-load pulse widths across these maps never exceeds 3.4ms. The only thing that does noticeably change is the amount of ignition advance which increases as engine speed decreases beyond lower than recommended tick-over speeds.
So either the ECU is switching across to the load fuel map when the tick-over sensor readings are outside of expected parameters to utilise its wider pulse widths, or there is something in addition to the fuel maps written in the ECU programming that can interfere with injector pulse width.



So perhaps having an excessively loose air port cable (instead of loose enough to ensure the port seal is never lifted off its seat unintentionally) would mean that when the handlebar lever is fully moved through its arc it could result in the air port only being opened a tiny amount instead of fully thus duplicating the Keihin/Triumph split rubber quandary. If this hypothesis is correct then in some instances on some bikes using the BI-Starter would result in a richer mixture.

[Thack]

ric writes: "The only thing that does noticeably change is the amount of ignition advance which increases as engine speed decreases beyond lower than recommended tick-over speeds."



Yes, this is a fairly simple system of idle stabilisation. Advancing the ignition timing from its "designed" value when the engine is idling causes the engine to speed up. Thus by advancing the ignition timing when the engine falls below the specified idle speed, you can speed it up again and bring it back into the correct range. Hence you have a fairly simple feedback loop to stabilise the idle.



At the moment I haven't instrumented the ignition timing on the B5, so I don't know whether it uses that system. I will be doing that this year and will report back fully, of course.



More modern bikes use a throttle actuator to achieve a fast idle, and idle stabilisation. I've done that on my B5 see the video here:

[Thack]

Oh, sod it! Sorry, by HTML skills are lacking. Just click anywhere on the coloured part of the text to see the video.

[papasmurf]

I have been suffering from backfiring ever since the doctor prescribed me Metformin.

[jefrs]

Neither the bypass not the bistarter can enrich the fuel themselves because the only place fuel comes in is the injector, they both provide additional air around the throttle butterfly but note the TPS still says zero to the ECU. They do however increase the air flow and that will be sensed by the MAP (manifold air pressure) which in conjunction with the TPS (throttle position), the CPS (Crank Position, revs) and the Temperature sensor presumably tells the ECU to enrich the fuel. So running it at idle for a prolonged session is probably not a good idea but to ride off and get the engine up to operating temperature as quickly as possible. I'm also thinking that switching on sequence primes the injector for starting, similar to tickling a carb.

[jefrs]

Thack - I've done a little experiment with the PCv's map#2 and made it do similar by making it alter the a/r and fuel when and if the rpm drops below normal idle. In short it works like your r/c gizmo but not as dramatically.



One method of curing overrun pop on the ECU/PCv is to kill the injector at zero throttle and high rpm, no fuel equals nothing to ignite but much of the popping is simply cold air expanding rapidly in the hot exhaust.

The other method is to monkey with the timing at zero throttle and high revs so the (little) fuel is burnt up and expanded before it hits the exhaust pipe, normally the combustion products are still expanding when the exhaust valve opens. Too advanced and you can ignite the compression stroke, oops.

Not having much luck with those two but I can make the idle hunt

[Thack]

jefrs writes: "They do however increase the air flow and that will be sensed by the MAP (manifold air pressure) which in conjunction with the TPS (throttle position), the CPS (Crank Position, revs) and the Temperature sensor presumably tells the ECU to enrich the fuel."



I notice you say "presumably" rather than "will", but I would reply by saying "Why?" One thing I would repeat is that no vaguely modern ECU needs telling when to enrich the mixture - it knows all it needs to know without relying on the operator for anything.



Secondly, any theories about it can only be validated by testing. And I've tested it: the bi-starter makes no measurable difference to the fuel injection pulse duration, and nor does the idle speed adjuster, except if you move the adjuster a long way out so the engine is racing and then you get a very slight increase, which (according to the O2 sensor) is just enough to use up the extra oxygen it's getting through the idle passage. In other words, it keeps the mixture the same.



We can all think of theories as to why the bi-starter could cause enrichment, and theories as to why it doesn't. But theories don't cut any ice - in the end, it's only objective evidence that counts.



The objective evidence I have gathered is unambiguous, self-consistent and in line with modern practice on other bikes. That's why I believe it.

[Thack]

Oh, just one little technicality: MAP stands for Manifold Absolute Pressure, not Manifold Air Pressure.



The reason it measures the absolute pressure (i.e. compared to a vacuum) is that it can then be used to measure the actual atmospheric pressure, rather than just changes in the manifold pressure due to opening the throttle. In this way it can calibrate the map to allow for altitude.



An air mass sensor would be even better, but significantly more expensive.

[ric]

Anyone noticed that the AMAL CARBURETTOR CONVERSION KIT (EFI MODELS) is only £250 + Vat

[jefrs]

The workshop manual calls the MAP the "Manifold Pressure Sensor" (quote), "The MAP provides instantaneous manifold pressure to the ECU. This is necessary to calculate air density and determine the engine's air mass flow rate, which in turn is used to calculate the appropriate fuel flow to the engine through the injector."

Different makes call these sensors by different names.



Enrichment (and a/r) is determined by the ECU based on its various sensor inputs. Its mapping is determined mainly by throttle opening and engine speed, as engine rotation increases, so it uses a different point on the map curve for fuelling. The PCv mapping is viewable in the software, it does indeed enrich fuel as revs increase. What tells the ECU to enrich the mix? - its mapping and sensor inputs do.