Re: TPS and a brief outline on the Engine management unit or ECU

Most ICEs(Internal Combustion Engine) must have less turning strain on combustion start and idle running,since sufficient rotational power is not there...for this reason the Ignition timing is set more retarded than under driving condition. This retarded timing also generates less power....so the moment the engine accelerates sufficiently the Ignition timing is Advanced to get more power and the higher RPM sustains it...so Ignition timing will be approximately 10~12 degrees BTDC(before top dead center) and depending on stroke length and engine design goes as much as 30~35 degrees BTDC. This Advancing of Ignition Timing is also necessary at higher RPMs, since the time for full combustion of the Air Fuel Mix becomes less and less with increasing RPM, and the only way to ensure near total combustion is to Ignite the AF mix much earlier...
In a Typical Carburetor engine the Initial timing is only to ensure easy start and reliable idle ..for saving the starter clutch most of the engines have a Auto De compressor on the Cam by which ,if the engine and Cam try to rotate back(back kick) a small lever on CAM will open the exhaust valve and let out the compressed gas...Present RE 350 has this mechanism on the CAM.....

Re: TPS and a brief outline on the Engine management unit or ECU

Got it. Yes the UCE REs has the auto decomp on the exhaust CAM.

But I am kind of perplexed, I have disconnected the TPS in my bike and still it starts quite effortlessly and I don't see any issues at higher revvs as well. So I asked, does it do so little a job that practically it's absence is not felt.

Re: TPS and a brief outline on the Engine management unit or ECU


Hello sir, I have a question about tps. As you might be knowing rtr's have a tps and hence a dual throttle cable setup.. Now a few months ago, tvs came up with a new TCI unit which eliminated the use of tps. This was done because the tps was going bad in many bikes due to dust accumulation etc and sending wrong signals to the tci unit resulting in abrupt jerking etc. Tvs claim that the new tci unit now incorporates the function of the tps unit and therefore the tps can be done away with. I have replaced the tci unit on my rtr with the new one(covered under warranty), so now the throttle cable goes only to the carb. How does the new tci unit sense the throttle position and vary ignition timing without having any input from the throttle cable? How does it work? :O
Also, I have observed a dip in mileage from 41-43(with tps) to currently around 37-40(without tps) in city with same riding style/conditions. :O

Re: TPS and a brief outline on the Engine management unit or ECU

When the Accelerator is at less position the TPS is at "0" position and the CDI assumes start/idle timing. It is when the accelerator is twisted that the TPS also change in resisor value to indicate the throttle position....Most bikes with CDI have built in failsafe map to fall back on IF the TPS becomes defective and gives wrong values...this is ONLY in Carburetted engines....In Fi engines if the TPS is disconnected then the ECU will throw an error flag and will not allow engine to be started /or in older versions, engine will start but cannot accelerate like before , and ECU will go into "Limp" mode.
Since in a carburetor engine , the Ignition timing is to be adjusted, between 10 degrees and may be 30 degrees, absence of TPS signal will start engine at 10 degrees, but will not be able to advance as much to 30 degrees...The Enfield Bullet being a long stroke engine has tons of torque and pulling power, due to which no significant change may be noted if TPS is disconnected.....Similarly I had disconnected TPS in my Karizma to experiment, and found only marginal difference...I even tried with the connectors in 180 degrees rotated connection....still only marginal difference...and on checking with timing light, found that only the maximum advance was reduced with these kinds of induced faults....engine still ran and performed marginally less ....Once again remember in Fi engines this will not be so and ECU will not allow the engine to either start or run....

----consecutive posts auto-merged-----

The RTR has IDI ignition system..ie., Inductive Discharge Ignition, as against Capacitor Discharge Ignition in most other vehicles.
The TPS in RTR is only like an On/Off switch like in Pulsars, but actuated by an additional cable attached to the Throttle cable.....This changing over of Ignition timing is for improving on both performance and FE...What the company had done now to eliminate the switch is to incorporate a circuit to switch Ignition Timing within the Module BASED ON RPM pulses, which is derived from the Output spark pulses. So the IDI ignition module is now sensing the RPM internally and the design had done away with TPS...
In other words, TPS signal is no longer needed, and an assumed Ignition timing based on RPM is now being implemented. This also explains why your FE had gone down...The change in design must have been done by averaging different Ignition timing curve in many different condition and a happy compromise reached....
The same kind of circuitry exists in most Older 2 stroke engine like RX100 KB100 IND-SuZUKI, etc, and in Hero Honda Splendour etc.,
This adaptation gives lesser headache to the manufacturer and the owner, but is a compromise over TPS design.....A properly designed system can overcome this ...
Here is a simple DC CDI circuit...note there are no connection for TPS. The circuit has Electronic RPM cut off at 10,000 RPM..
The Circuit has auto Ignition Timing .

Re: TPS and a brief outline on the Engine management unit or ECU

[MENTION=32286]psr[/MENTION] Thank you for the clarifications. Reading through your comment another question popped up which is not connected to TPS. Does the auto decomp engages only during the kick backs in Enfields? AFAIK they only engage till certain RPM and are thrown back once the RPM rises above that particular RPM.

Please clarify sir.

Sent from my 8x-1000 using xBhp Connect mobile app

Re: TPS and a brief outline on the Engine management unit or ECU

The Auto De-Comp is integrated into most 4 stroke higher cc bikes,with Self starter to prevent fierce back kick,which will also kill the starter clutch mechanism ,and starter over a period of time....It works only when the engine tries to turn in reverse ,or on low RPM,(non Idle) and the off set weight on the cam lifts a lever which opens the Exhaust Valve , to leak the compressed gas in the combustion chamber.

The Enfield Auto de compressor on the exhaust cam...


here is a video to explain how it works...

Re: TPS and a brief outline on the Engine management unit or ECU

Thank you [MENTION=32286]psr[/MENTION] sir for all the replies. I had seen this video before but never knew that during kick backs the auto decomp engages

Sent from my 8x-1000 using xBhp Connect mobile app