Forum

[Thack]

Ric writes: " Personally I'd opt for a cheaper and very simple setup that adjusts the output values from the Lambda sensor so the ECU constantly trims the AFR to say 13.7:1 instead of the [anaemic] 14.7:1 it is currently set for."



Yay! That is exactly what I am aiming for myself, as the next phase of my "black box flight recorder" project. All the essential data logging is finished. I have shown that - for some reason I can't fully explain - Keihin set the engine to run somewhat rich at sub-1000rpm idle speeds. In fact, the slower the speed, the richer it gets. This makes it very difficult to attain a stable idle at around 700rpm, compared with how easy it was with the carburettor engines.



After a lot of messing about I decided the easiest way to modify that was to tweak the O2 output voltage in order to fool the ECU into thinking the engine is running richer than it really is.



Above idle it runs at 14.7:1, just as you'd expect, so my tweak will only kick in with a closed throttle and sub-1000rpm engine speed.



Once that is settled in, I can then explore tweaking the mixture in other ways, along the lines Ric suggests.



The final phase, after getting the mixture under control, is to finish off the data logging side of things with stuff line an accelerometer, a bank angle sensor, a GPS unit, and some other bits and bobs.

[Thack]

Oh, to answer RoSy's question: Ric is right to say that the Enfield runs closed loop (MOST) of the time, and thus can easily compensate for a change in the exhaust system.



The reason most suppliers recommend a PC-V with a different exhaust is because you can't benefit very much from the different exhaust (some, but not much) unless you take control of the mixture as well. Thus they are a logical pairing.

[Presto]

Sorry Thack that didn't help at all. If Mr H goes to some length to warn against using non-standard exhaust then some folk are building up problems by ignoring that experienced advice.

[ric]

Presto, Is it that difficult to believe that an electronic system capable of coping with the barometric difference between the Khardung La at over 17,000ft and a British coastal road down at sea level to provide a constant Air to fuel ratio within the combustion chamber cannot cope with a simple exhaust change?

[ric]

Thack, don't forget tyre pressure sensors

[Michael]

PeteF... I have checked and checked and checked for air leaks in my exhaust system - none can be found. But I think there are other possible cuases for exhaust backfires. Mine backfires when the trhottle is closed sharply from a mid-high position. The pop occurs just as the throttle gets back to the idle position, but as the engine is still at high RPM (is this over-run?), especially when the bike (and therefore exhaust bend) is warm/hot.




I *think* it occurs at this point because the mixture leans out suddenly as the injector essentially goes to idle mode. Moreover, there is a sudden effective vaccumm in the cylinder at this point also, drawing in more air thourhg the intake and through the still not-fully-closed exhaust valve. This never happened on the original silencer, as it is very restrictive and so does not allow air to be drawn in via the tailpipe very easily. However, the free-er flowing Hitchcocks silencer (expecially without the baffle) allows far more gas flow and so air can be drawn *in* more quickly through the tailpipe when there is an effective vaccuum resulting in a temporarily lean mixture and hence backfire. This might all be nonsense, but my exhaust doesn't leak - I really have checked - and this explanation keeps me happy

[ric]

Micheal, do you have an active PAV on your bike ???

[Presto]

ric, I'm not going on theory but experience. But if you know better then all well and good.

[Michael]

What is a PAV?

[ric]

A Pulse Air Valve, it feeds air into the exhaust manifesting itself as an air leak with the exact symptoms you have described. It's usually only active on very low and closed throttle applications.