Query Moved and Approved.

is TPS the idling speed adjustment????

Nope u cant.

Damn. Coming from you, I think am gonna quit trying!

How much of a disadvantage you think it is, Joel?

And any ways to offset it? Some dynamic timing is always helpful...

Very simply put, its the sensor that senses the position of your throttle so it can adjust the ignition timing.

U can set it to static. if u changing the carb, twist the TPS switch to max throttle position and lock it with some glue or so. It will run a static map, but no issues. For out right performance, the WOT map is what matters. Lower positions are for low down power.

!!!

I knew there would be some kind detail I would be better off knowing. Thank you! I just hope its not too drastic at WOT. Am looking for a street friendly mod. Considering the ZMA, I believe it would be a bit more advanced at WOT setting??
I may be asking for too much, but for knowledge sake, how much do these boxes alter the timing anyway?

HI,
Can you post some pics of the TPS on your ZMA. That may help some of us give you our opinion.
Regards,
Siddharth

Normally on most 4-stroke ignition set-ups, the ignition timing retards as the rpms go up. However that cant be the case on a race engine. Timing retard/advance is based on the requirement.
The karizma gets into a retard dynamically as the rpms go high, courtesy the TPS switch.
Now, its not that you cannot have your TPS anymore if you switching the carb. if you have the idea to implement or replicate the same throttle positions as per the movements of your new carb slide/butterfly....its done.
If you using a slide type carb, its very difficult. U will have to make an external TPS switch operated off a cable activated mechanism. More like what comes in the RTR. However that switch should be competent enough to send the right signals.
I've personally taken off the TPS switch and there was nothing noticibly lost in the low-mid revs. And our engine was anyways never ridden below 5000rpm mostly.

That settles it then. This is one of those rare occasions when you get all the answers you need without finding out the hard way

Thank you. End of that story. Am sticking to WOT setting.

But I'd like to prod a bit on the advance/retard thing you mentioned. I have been pondering over that.


Unlike what you said(which I have assumed to be true), I always thought thumpers went for advance at higher revs, considering the time available for flame-propagation goes down, and the time required for it stays the same. I guess its the higher turbulence that speeds it(propagation) up at higher revs? This theory always confused me. Sounds to me like the lower available flame-propogation time at higher revs is auto-compensated by the higher turbulence which reduces the required flame-propagation time. But then how do you which way the scale is tilting? Are different engines divided on this front, based on their various parameters? Or like you said, ALL four strokes go for retard?

As far as I understand, old brit thumpers go for advance. They surely don't come under race engines..

Am a bit lost here and people I ask either don't know or don't know that they don't know.

If you would just type some more words of clarity...

Look, we want the bang at TDC. At higher rev, the time available for flame-propagation goes down, and the time required for it stays the same. So, we start earlier. Hence, timing needs to be advanced.

Also at higher revs, cylinder efficiency decreases due to valve train limitations. This means, charge is rarer in density compared to lower rev. This again increases flame propagation time. So, we need an additional advance due to this reason too.

Race engines typically use turbochargers. Denser charge needs lesser flame propagation time. So, they require the timings to be retarded compared to normal engines. Same if the CR is increased.

And, all engines display basically the same characteristics.

If the timing is too advanced, detonation occurs! So, beware of using that WOT timing. At least check for detonation under load at lower revs.

The timing retards - you mean the time between the spark and TDC decreases as rev increases?

May I know which bike you are you taking about? I have never heard of that till date!

FYI, on P150/180 UG II/III, it is -
10 BTDC @ 1500 rpm
28 BTDC @ 3500 rpm

As you can see, the timing is advanced.

You may want to look here, even though this is not my source of knowledge.

I think you made a typo there.

You have the timings for the Zma?

Even I have encountered various schools of thought in this case. And most of them don't know the existence of the others.

I believe a lot of two stroke engines prefer to be retarded at higher revs, but then this is based on no concrete facts, just the spoken word.

Its such a critical aspect of tuning yet so fogggy.

Hope someone will set this straight once and for all...

Thanks everyone so far, it sure has helped.

Yeah that is true fact. Two strokes like their timings to be retarded as rpm increases above a certain limit.

To give a clearer idea, the timing goes like this -

2000 15 BTDC
3500 25 BTDC
5000 15 BTDC
10000 9 BTDC
12000 7 BTDC

This is very different from a 4 stroke engine timing curve. The advance upto mid rpm allows the bang to occur at TDC - same reasons as 4 stroke. As rpm increases further, timing is being retarded instead of being advanced.

At higher rpm, the theory in this case is different from 4 strokes. While it is true faster the piston, moves the earlier the ignition needs to fire to create optimum combustion, but in 2 stroke engines, exhaust pipe plays a significant role. If we retard the timing at high rpm, that is, bring it closer to BTDC, the bang occurs later. This may seem to be wrong. The effect of this is that the piston stays cooler but the exhaust pipe gets hotter. This increase in temperature of the pipe causing the pressure wave to travel faster (change in the speed of sound is directly proportional to square root of the change in temperature). When the wave is able to travel faster than before, a pipe tuned to say 10000 rpm actually acts as a pipe tuned to say 11000 rpm. Hence, net result is an increase in the powerband ceiling, ie. the powerband is effectively widened.

So, we retard timing at higher rpms (same as around the pipe resonant frequency) to utilize the supercharger effect of the pipe. This benefit outweighs the loss due to the bang occuring after TDC. Actually peak power does decrease a little.

Similarly, say you want to widen the powerband in the opposite direction too, ie. you want power in the 5000 rpm region using the same pipe tuned at 10000 rpm, what do you do? Simple, you cool down the exhaust pipe - yeah that is right. This is exactly how Honda experimented with water injection. Also add a little extra advance for further help!

Another reason that tends to decrease advance as rpm increases is the increase in turbulence. Turbulence in 4 stroke engine is not significant enough to affect timings but in case of 2 stroke engine it is an important
factor.

And I think I do not need to tell about the advantages of a wider power band in case of a 2 stroke engine.

Hope I was able to clear this up. As you see, no magic science. But people in the know are reluctant to divulge these informations - something to do with trade secrets they say.