Hitchcocks Forum

we were out yesterday for a ride (me on my 2006 Classic, which blew its head gasket on the way home) with my mate on his 2014 Classic... hes just got it and its brand new (long story) but on the OEM exhaust. We saw a lovely Wassel 'tulip' turn up silencer at a small dealer.. my question is.. will the EFI unit get too bothered with the less restrictive silencer, will it self adjust?

Yes it will. The ECU will run weak without the stock exhaust, mine did. You need the Power Commander to fix that.

H's PCv comes with exhaust sensor blanking plug and 'dongle'.

If you run without the ECU with a free-flow exhaust, you will blue the down pipe, that means weak mix.

Ok, wife killed the internet in the middle of that

The stock exhaust is not only restrictive but weighs a ton. The silencer is like lifting a log and it's ugly.

The stock down pipe is about twice the weight of H's replacement part, thick wall.



With the stock exhaust the C5 not only lacks power but the EFi makes the bottom end lumpy. Some of the lumpiness can be dialled out on the bypass screw. A free-flowing exhaust improves matters further but will now run weak, requiring the PCv.

The result is not so much more power as smoother running.



H's PCv maps were developed for the EFi with various stages of tune, they are custom maps and not found on the PC website. I understand they looked ad the AT-200 Autotune add-on but found it didn't bring anything to the party unless you are very keen on tuning.

Sorry to drag this one back out from last month, but I've only just come across the information again I'd previously seen which was factory provided during the launch of the new EFI models...

EFI system is the Keihin brand, used in Honda motorcycles and scooters
Fuel injection mapping is able to process at altitudes up to 18,000 feet
Muffler can be changed without remapping fuel injection

Reading the sales brochure keihin Electronic Fuel Injection is only specifically stated for the Continental GT, all other have 'electronic fuel injection', perhaps a cheaper variant?
Different re=mapping for 2014?

Should read 2014 Classic?

can you explain 'by dialing out on the bypass screw' ?

Dialling out on the bypass - this is a brass slot head hidden under the seat, loosen the jubilee and rotate the throttle body towards you to gain access. I found almost a 90° turn made the initial pickup much smoother. Not so on/off on the throttle. Do check cable slack with handlebar turn. This raised the idle by 50-100rpm (I have tacho), not significant: all motors will vary.

In some ways this is like dialling in a SU/Solex carb, they have an idle screw and air bypass to fiddle with.



Exhaust re mix - The ecu will adapt mix to some extent if you change the pipe. I ran the 50s free-flow exhaust without the PCv and the down pipe blued, which indicates too hot due to weak mix. PCv seems to have stopped further bluing, the chrome is now turning a coppery colour. Mix is now correct, I think. H's 50s pipe may be a little more free-flow than the ecu's O2 sensor can cope with.

There is the Autotune AT200 add-on gizmo for the PCv which is supposed to fix the mix on the fly but H reckon their dyno-developed maps don't need it. We only go up to 300 metres here at the top of White Down. Whilst I like the concept of the AT200, H reckon it doesn't bring anything to the party.



India has 'orrible petrol and yes, they do take their bikes up the Himalayas, so they probably do need the ecu to adapt to conditions.

Another cause for excessive pipe discolouration could well be retarded ignition which would have a less than beneficial amount of fuel still burning as it leaves the combustion chamber transferring more heat than usual through the downpipe.

At some point I intend to advance my ignition with the aid of an ElectraX stepped woodruff key to see if the blueing I have on my stock B5 recedes. The bike feels as if it's running retarded despite managing to hit the rev limiter in top gear along a flat (private) road. A few degrees should perk things up and hopefully be beneficial at tickover.

The current C5 is ecu computer, I have absolutely no idea how its ignition is advanced or retarded. Magic probably, this is despite having met some of the chaps that invented the 'integrated circuit'.

H opine this bluing is weak mix and is normal ecu behaviour into the 50s free-flow exhaust without the PCv.

I also believe it may be the 'pulsed air system' (internal on current Efi) popping too much air into the outlet whereupon it bangeth, pops and crackles from time to time (no leaks there). So perhaps not weak in combustion chamber but weak (hot) in exhaust down pipe.