Stupid question time
 

Well I'm stupid and I'm not ashamed to admit cos I guess that I'm not the only one who doesn't know.

Several people write on here that their bike sounds really good 'on the overrun'.

What is the 'overrun' please? When/how will I know when my bike is 'overunning'?

Ed

Re: Stupid question time
 

Not stupid. No question is stupid. If you dont know something, you dont know something! SO its good to ask!

I think overrun means when decelerating off the throttle...least, thats what I've always taken it to mean and everyone seems to understand what I mean when i tlak about the sound on the overrun

I dont know why its called overrun though...

Matt

Re: Stupid question time
 

My dear Mr. Watson. You are indeed correct. Overun inside a tunnel is best!

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as above

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Yep, NOT A STUPID QUESTION at all.
It can also happen when you are going down a hill and you throttle back.
Bike doesn't speed up or slow down , but the revs stay up.

Think thats what it means!?

Re: Stupid question time
 

Yup as said, overrun is when you come off the throttle. What normally happens is that the engine tries to slow down, but the momentum of the bike keeps the speed up. As a result, rather than the engine driving the rear wheel, the rear wheel is driving the engine - hence overrun.

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No No No, a stupid question would be.

If a carrot and a cabbage where to have a fight using only cocktail sticks as weapons, whilst balancing on the head of a Dodo, what temprature would it be in Cork.

Now thats a stupid question :lol:

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Very interesting, thank you peeps!!! I'm going to experiment this morning but sadly we have no tunnels in these parts.

Perhaps others have some 'stupid' quezzies - fire away...

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Basically, for a given throttle position, the engine is running faster than the speed of the bike, so your effectively using it as a brake. Drop a gear or two as you're slowing down, close the throttle and let the engine take the strain.

Depending on the mapping, you'll get bangs & pops from a race can. This is unspent fuel in the exhaust which is igniting with the hot gas being expelled. My old Gixxer 600 would shoot flames out the back if I got it right.

V-twins sound really good in overrun, fours not always as good, but my 'Blade still manages a crackle or two with the stubby can on.

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Mmm overrun on a twin in a tunnel, pleasant to the ears :D

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I can confirm yours does sound good on overrun Ed. Find a nice long steep hill and take your earplugs out....

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The cork would be 298 kelvin

Matt

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No I reckon it'd be 25 degrees C to the nearest whole degree ;)

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Overrun noise shouldn't happen on modern bikes anymore, it's just the unburnt fuel popping in the exhaust etc that would normally be making the bike idle. Fuel injection ECU's just cut the fuel completely when not needed so no pops and bangs.

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My K4 sounds like an excursion into no-man's land when I'm throttling off, tunnel or no tunnel :cool:

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Somebody better tell my ECU that then.... 'Cause it crackles and pops on overrun, and last time I looked, it was EFI and EI....

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Ditto here... K6 F.I. model and I get blue flames while decelerating... ummm... 'on the overrun' at around 4k revs! :cheers:

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I've got twin Scorpion cans on my VTR. They sound awesome!!

Anyway, getting to the point, after I cleaned the exhaust system back at Easter, I didn't quite fit the rear pipe "just so" in the manifold. This results in it sucking a small amount of air in on the overrun and combining it with the unburnt fuel. The resulting pops and bangs and occasional flame or two make for great entertainment :cool::cool:


Sounds great too!!!!:D

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Here's a question- is EFI electrical Fuel Injection and EI Electronic Ignition?

Mine used to make great pops on overrun. Loved it.

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Yeah, I was too lazy to type it all out :rolleyes:

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When you shut the throttle the fuel should ideally not be cut off. You still need a small amount of fuel to keep the ports 'wet'. Otherwise the throttle response when you get back on the throttle wll be very jerky. On our race car we actually keep fuelling when you come off the throttle and just cut the spark - flames like a bugger but it keeps the temperatures down in the cylinders.

Re: Stupid question time
 

It all depends on the mapping... If you're throwing too much fuel in to start with, you'll get more unspent fuel in the exhaust system. Many cars & bikes that are remapped often provide too much fuel at some point, so when you come off of the gas there's still plenty in the chambers to be expelled, it gets hot, meets with oxygen and then "pops".

My car does it, even before the remap, and it certainly does it now.... Must work on the flames, that'll be cool :)

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Why did the chicken cross the road?


No, really!

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Overrun is when rotating parts unscrew themselves cos the bike is driving the
engine and not the other way round. You find the bits at the bottom of hills.

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Wasn't there something that you could buy that ignited the hot gases out the back of the Exhaust? Something like a piezo fire lighter. I'm sure I've seen that somewhere!

You press a switch and it ignites. Not too sure if it will do it on a normal car but a heavily tuned one it might.
:driving:

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You mean this:

http://www.akamoto.co.uk/flaming-exhaust.asp

I read about them when they first came out and they cost a packet then but they weren't strictly legal nor illegal. I'm sure the fuzz would do you for something though.

Anyone been successful at backfiring their SV by flicking the kill switch off and on? Never tried it myself.

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yes............. all the time

bryn glas tunnels & the dover ferry spring to mind

its much fun, i think i made a boy racer soil himself as he was acting cool sat on his subaru bonnet

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This is why i like the PAIR system, it causes lots of pops on overrun at about 4k revs \\:D/

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Overrun... think of it as when the wheels drive the engine, rather than the engine driving the wheels.

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Well thank you peeps. I've tried it, and yes it is good:cool:

Fess up time. I still have the baffle in my can - it's a CCC. So now I'm going to take it out.

Muppet - your sig. I saw it the other day and I now ride around wondering which of the brainless morons around me don't even know I'm there.

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AQA ??!!!

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:cool:
Excellent! Very glad to hear this. My last few cages have all been 'entertaining' on the overrun, tunnels a speciality!:smt045 So I am pleased that the SV will carry on the grand tradition at chez Ace-T :D

Trace :)

Oh and re the 'device' to ignite the unburnt petrol, I have seen a common or garden spark plug inserted into the exhaust to ensure the effect, not sure of the legality though, strongly suspect it isn't :D