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[Deanobats]

This is a very interesting thread. I was thinking of swapping the standard exhaust (pipe and silencer) on my 2015 Bullet B5 for this one as a few bits have already come adrift on the one it was delivered with, and I wanted something that I could use without adding a power commander (Our hosts says this one will work without). The reason I bought an Enfield was that I wanted something I could have fun adapting and modifying, enjoy the process and also learn from. It was (relatively) cheap for what it is and with endless possibilities for customisation. If I'd wanted something that was fine out of the box but that had to be taken to the dealers for anything other than an oil change, I'd have bought something Japanese.

[jefrs]

If all you have done is change the silencer then you probably /do not/ need the PCV. That happens when you change the entire exhaust system and add the K&N air filter, then the ECU cannot cope. Reports from elsewhere strongly suggest the stock ECU can cope with a silencer swap.



The ECU has a narrow-band Lambda O2 sensor which can only make gross changes in mix, "make it richer" but not tell the ECU by "how much" like the wide-band Bosch O2 sensor does on the AT-200 Autotune - which is something I'm experiments with to cure popping properly and to improve cruise (which region is not covered by the supplied fuel map).



Main cause of popping after fiddling with the exhaust will be an air leak.



The inaccessible brass screw can be got at by rotating the entire throttle body towards you as per workshop manual or finding a long thin bent screwdriver. This device appears to be a form of secondary throttle to adjust idle speed, it does not enrich because it is in front of the injector but will increase air-flow through the sensor which may well cause the injector to pump more. Increasing idle a little may reduce popping, I found it made pick-up from zero throttle smoother.



However, popping may be caused by too-rich mix hitting the exhaust and going bang. When air gets in the exhaust, the sensor sees diluted and hence weak mix and so makes it all richer, doh.



The Hitchcocks PCV map does add more grunt and is smoother but does not cover the 0% and 2% throttle columns where the popping occurs, that duty is handed back to the stock ECU. It does however get the mix better for the modifications and hence does reduce popping most of the time.



I would ensure the exhaust system is sealed up tight and tweak the idle screw before buying more toys.

[jefrs]

Papasmurf's link to the injector PR is very interesting but do note the current (2015) is a somewhat different motor from 2011 on, stronger with more grunt, different mapping. One reason for remapping with the PCV is we do not climb to 18,000-feet in Britain.



A reason for changing the tow-a-log silencer is the thing is pug-ugly, plus it is very heavy too.

[2cvandy]

I've read this thread with interest mike w as mine already had this silencer fitted when I bought it. Mine also has the exhaust oxygen sensor removed and a resistor fitted in it's place but no power commander. Mine also pops on the over run, if I shut off too quickly downhill from 60mph (ish) I also get the occasional back fire, all exhaust joints are sealed though, it's not blowing from anywhere. I find it quite endearing to be honest, and having read through the post I think I'll leave it as is and just enjoy it as character!

I do, very rarely, find it lacks pick up from a closed throttle though so I will investigate raising the tick over slightly, thanks for the tip jefrs.

[Rattlebattle]

I quite like the standard exhaust on mine, but it is black (LE Despatch) so to my mind looks better than the chrome equivalent. I like that it is quiet (ish) but it does have a bit of a bark to it when the throttle is opened up. FWIW I've slowed down the tickover (using a long slim screwdriver) and as a result the gear change is better as the revs die more when closing the throttle. Having tried the O2 sensor eliminator I have switched back to standard as the engine ran rich. It now starts easily and runs very nicely. It seems to me that individual engines on these UCE bikes do run differently; I stand by my comment that just putting a more free flowing silencer on an otherwise standard EFI bike is likely to cause mild popping on the overrun. This isn't harmful and is arguably endearing. Whilst welcoming the chance to fiddle with the bike to get it to run nicely I myself do not wish to shell out over £300 for a PCV, that's all. My RE is not my only toy; for what it is it runs very nicely as it is, after a bit of tinkering.

[jefrs]

Yep, if you just remove the O2 sensor and fit he resistor then the AFR will be all over the shop. I can see this in real time with the AT-200, ratio anywhere from 11 to 20. You either need the stock Lambda or a mapped PCV (or PCV plus AT-200 with the wide-band sensor). The stock Lambda O2 attempts to maintain a stoichiometric mix of 14.7:1 at all times on the RE Keihin map - which is not ideal under all conditions.



Work in progress but the AT-200 /is/ capable of curing the over-run pop and crackle completely. I got it to do that perfectly once but it was negating the Hitchcocks map. It was ever-so smooth but needed some fire in its belly. So back to the drawing board, well spread sheet anyway.

[jefrs]

Why do I shell out for the PCV and a similar amount for the AT-200, because I can and kinda old-job related stuff I can do standing on my ear - figuring numbers out. Peering at four or more seemingly unrelated tables of numbers and making some semblance of sense from them, and then deducing what needs to be altered is not for everyone. If had I wanted a fast bike I would have got one, and then I figured I can make this one work better.



Mild popping might be acceptable although it does frighten horses when the rider is asleep. Loud 'back-fire' banging is not and indicates something is probably wrong.

[mike w]

Thanks for all the useful comments ref new silencer, spoke to Hitchcocks today and they are really helpful suggested extra gasket at top of pipe , and explained the merits of the PCV unit but did not try to push it For me to buy one though I would not discount the idea. They explained the silencer should work for the bike I have but can't guarantee it as not all of the bikes are mapped exactly the same (I am not sure if that was exact terminology as I got a bit lost on some of the technical details).
Where as the popping is in endearing as one reply said its a bit of pain on the back roads approaching horse riders and I am thinking s##t is it going to scare the things into some stampede. I suppose as I have only ridden Jap bikes before where the only clue that the engine is running is the fact I am moving, maybe I should except the noise and kid myself I am riding a 50s bike. Once again thanks for all the feedback.

[mike w]

Just seen you're last reply jefrs and are you saying the PCV unit is a good thing please excuse my ignorance but as explained in a previous post I am do not have much mechanicall knowledge and some parts of the replies are totally lost me, though I did grasp some of the info Hitchcocks gave today

[sofiaspin]

One example of an EFI engine with after market silencer and nothing else was the Watsonian built Woodsman. They fabricated or sourced a high rise pipe that was 'open' - some baffling to allow for back pressure but enough to boost BHP marginally and give it a decent bark. I had one, and it ran very well, very occasional popping on the over run. No need for a PCV or any of that fuel management gubbins. Hitchcocks test their products and I would defer to their advice on this - which sounds like - fit it, seal it, ride it.