What did you do to your bike today?

TallPaul_S · 13 Jun 2016 at 09:35

Dogbreath said:
Are you certain that you haven't either bent a disc or the caliper mount on the forks? That's the usual cause of this kind of problem. Also check that the bobbins on the floating disc are free.

Nah it's not that - the lever feels the same no matter if the bike is moving or not. You can actually see the pistons going back in after the lever is released.

On the ride in this morning the lever was nice and firm, so much so that I had to adjust it towards the bar a bit. It'll stay firm for a while but eventually get softer.

Craig321 · 13 Jun 2016 at 09:56

Does it get softer and stay softer, or does it get softer and then firm up after you've used it again?

tom_e · 13 Jun 2016 at 09:59

The innuendos that are flowing through my mind right now

wazza300 · 13 Jun 2016 at 10:16

Pistons are probably getting clogged with brake dust ect,some braided lines might help

Rubber hoses tend to expand more with age

TallPaul_S · 13 Jun 2016 at 10:33

Craig321 said:
Does it get softer and stay softer, or does it get softer and then firm up after you've used it again?

Gets soft and stays soft - imagine it like the biting point is moving an inch or so towards the bar.

tom_e said:
The innuendos that are flowing through my mind right now

No-one likes a soft and floppy thing in their right hand... :eek:

wazza300 said:
Pistons are probably getting clogged with brake dust ect,some braided lines might help

Rubber hoses tend to expand more with age

Probably exactly this, if I did rebuild/replace the calipers I'd fit some braided lines too as I know they will firm up the lever action.

The brakes were working a little better this morning, a bit more bite it seemed, I may just have to keep taking them off and cleaning them every month or so.

cyclops12 · 13 Jun 2016 at 10:42

unKle said:
It's more than likely the Secondary Air System (SAS) that you're hearing on the overrun, loads of bikes have it.

The only way to stop it is to get a kit which comprises of blanking plates and hose blocks so you can do away with the SAS.

Yep spot on, it's called the pair valve on the Busa.

It's a common mod after changing the cans from stock, just a couple of blocking plates stops it completely.

tom_e · 13 Jun 2016 at 10:43

I considered doing it on the SV but then I like the snap, crackle and pop in the morning.

.one. · 13 Jun 2016 at 14:25

TallPaul_S said:
Probably exactly this, if I did rebuild/replace the calipers I'd fit some braided lines too as I know they will firm up the lever action.

If the you suspect the hoses are swelling you can feel them when pulling the lever in changing to braided on an old bike is night and day for firmness.

IC3 · 13 Jun 2016 at 14:45

misterjingo said:
I'm not sure either - the guy who suggested it said lack of back pressure due to removing the baffle? Although someone else said he was talking **** .

Perhaps I'm looking for reasons to mess with things? .

If you're talking about your Husky, than I don't see anything strange in pops and crackles. My Mates MZ was shooting flames and popping like mad! :cool:

acemastr · 13 Jun 2016 at 18:17

misterjingo said:
A few newbie questions here...

I de-baffled my bike (akro exhaust), and there's a lot of popping on deceleration. Someone suggested that this could be due to the bike now running lean.

I'm going to check my plugs tomorrow to see if there's any signs there.

If it is running lean, is it a case of rejetting to a bigger jet size? I've watched a few vids on this and it seems pretty straight forward. Can you get jet kits, or are they bike specific? Also, how'd you know what jet size to use - trial and error?

Also, if you rejet, do you have to do anything with the needle?

This is all new to me, but am happy to have a mess/play .

You'll actually find this is a flame out the back (ride and night and look) and is caused by air igniting, the same thing happens to mine with the baffle out and mine is properly tuned.

Enjoy it, it looks awesome at night

TallPaul_S · 13 Jun 2016 at 18:27

It won't be flames all the time, if any in fact. Popping does not equal flames.

Popping is just unburnt fuel igniting in the exhaust, with the baffle out it's free-er flowing so more of the unburnt fuel is exposed to the air.

You'll know a flame when you here one, it's like a big backfire or loud single pop.

IC3 · 13 Jun 2016 at 18:35

I'll record my SV, how it shoots flames.

just persia · 16 Jun 2016 at 20:43

Fitted a decat pipe.

Flack88 · 16 Jun 2016 at 21:04

Could do with one for my CBR however its not possible without replacing headers.

acemastr · 17 Jun 2016 at 19:20

Rebuilt the YZ125 top end, really an easy job on a 2 stroke, 90mins of work.

acemastr · 17 Jun 2016 at 19:21

TallPaul_S said:
It won't be flames all the time, if any in fact. Popping does not equal flames.

Popping is just unburnt fuel igniting in the exhaust, with the baffle out it's free-er flowing so more of the unburnt fuel is exposed to the air.

You'll know a flame when you here one, it's like a big backfire or loud single pop.

I do beg to differ, a blue flame is air igniting, mine pops and gurgles and puffs out a flame all the time. It isn't always fuel.

TallPaul_S · 17 Jun 2016 at 20:25

acemastr said:
I do beg to differ, a blue flame is air igniting, mine pops and gurgles and puffs out a flame all the time. It isn't always fuel.

How exactly does air ignite? Air is mostly Nitrogen and Oxygen, both of which are not flammable.

Pops and flames both happen when the throttle is shut because there's less air being pulled into the intake, which means the fuel cannot ignite and passes out the exhaust valves into the exhaust. On meeting the air in the exhaust and hot exhaust pipe, it ignites. More fuel = bigger pop, or a flame. Some fuel, little pops and no flame.

A blue flame just means there's not much fuel in the mixture that's igniting. An orange flame (which some bikes produce) means more fuel.

So my point is correct, you won't get a flame all the time when the bike makes popping noises as there's only a small amount of fuel igniting somewhere in the exhaust. I doubt my bike, which will pop on the overrrun for a good 3-4 seconds without issue, is shooting a flame out for all that time. Now if I hit the rev limiter I'm pretty certain I get a flame with a LOUD single pop though.

CGrieves · 17 Jun 2016 at 20:59

TallPaul_S said:
How exactly does air ignite? Air is mostly Nitrogen and Oxygen, both of which are not flammable.

Technically yes, although combustion is oxidisation, i.e. the re-uniting of oxygen with fuel. So although we consider the fuel as being burned, it doesn't happen without oxygen (or another catalyst).

The valve overlap on a performance four stroke, i.e the time during which both the intake and exhaust valves are open, means that mixture can get through to the exhaust. On a mid-90s onwards bike (earlier with some US models) the pops are air being injected into the exhaust by a PAIR-type valve to try to completely combust that unburnt mixture. It means "cleaner" exhaust gases, and also prevents the mixture destroying any catalytic converters. On a carbed bike you'll get more popping because the idle circuit always draws some fuel even with the throttle butterflies closed. Most injected bikes run with complete "fuel cut", i.e. when decelerating there is no fuel being injected (unless you remap).

Fun fact, in a typical combustion cycle in a modern engine, the air in the mixture weighs more than the fuel.

TallPaul_S · 17 Jun 2016 at 21:27

Agreed.

Obviously you need air and fuel for combustion, but then acemastr did say a blue flame is air igniting, which it can't do unless there's fuel present

it's pretty simple really - unburnt fuel in the exhaust has to meet air at some point, whether that's early in the exhaust due to a leak or air injected, or towards the end with air being pulled in.

Question though - why do BMW's have that distinctive pop (and flame occasionally) when the throttle is closed? It's either an auxiliary air system or they're just dumping fuel into the exhaust for the hell of it

CGrieves · 17 Jun 2016 at 21:37

TallPaul_S said:
Agreed. Obviously you need air and fuel for combustion, but then acemastr did say a blue flame is air igniting, which it can't do unless there's fuel present

it's pretty simple really - unburnt fuel in the exhaust has to meet air at some point, whether that's early in the exhaust due to a leak or air injected, or towards the end with air being pulled in.

Question though - why do BMW's have that distinctive pop (and flame occasionally) when the throttle is closed? It's either an auxiliary air system or they're just dumping fuel into the exhaust for the hell of it

It's the PAIR (or whatever BMW's acronym for it is, I'll check the manual). To meet Euro3/4/5 regulations and make any power, you have to have a catalytic converter, but unburnt mixture will destroy a cat very quickly so the air injection circuit makes sure as much mixture as possible is burnt. The Beemer runs a fuel cut system anyway (except in Slick mode where the throttle is essentially kept slightly open to reduce engine braking) so the pops happen at the instant the butterflies close and the cylinders are purged. There's also a secondary pop as the engine passes 4K rpm or so, possibly when the exhaust butterfly closes but I'm not entirely sure. I know I like it though

I'm actually looking for an aftermarket exhaust at the moment, but for the first time in my riding life it's to reduce the noise. I'm at Snetterton in August, but last month there I got black flagged at 106dB on the pit straight noise meter.... limit is 102db and roughly every 3dB is double the noise