popping on the overrun

[galois]

My car has just returned from a long visit to the local garage (work and space meant I couldn't do it myself). While it was there they said they did some re-tuning to clear emissions. The car now fizzes along at high revs   , but has started to pop and bang on overrun   . Should I be concerned at all or should I just enjoy this new tuneful approach to motoring?

[Paul Hurdsfield - Joint Manchester AO]

Enjoy it, it's great isnt it?  

[langy]

take a drive at night and see if you are spitting flames as well    mine does !

[pete g]

poping is a sign of a weak mixture on over run

not a problem

[Tango Squadon]

Throttle butterflies not balanced?

Mine used to sound like artillery barrage on over run. Great!

[galois]

Great - sounds like there is nothing to worry about. Just smile and enjoy!

[Captain Colonial]

Soon you will learn how to do it to order, i.e. hard throttle followed by sudden full lift-off gets big bangs, etc., and when to do it to maximum effect, such as setting off car alarms and scaring the nervous or jumpy or drunks or hoodies.  There's an art to it.  Nothing more satisfying than a night blat and seeing flames light up the roadside.

[Doug Dastardly]

poping is a sign of a weak mixture on over run

not a problem

I'd always thought popping as described was a bit of unburnt fuel igniting in the (hot) exhaust?

But I'm the first to admit I'm no mechanic....anybody have the definitive answer?

No criticism intended for original post,or Pete, I'm just interested.

[Dave Eastwood (Gadgetman) - Club Chairman]

Soon you will learn how to do it to order, i.e. hard throttle followed by sudden full lift-off gets big bangs, etc., and when to do it to maximum effect, such as setting off car alarms and scaring the nervous or jumpy or drunks or hoodies.  There's an art to it.  Nothing more satisfying than a night blat and seeing flames light up the roadside.

It's one of those great motoring pleasures, setting car alarms off with a bit of well timed exhaust play    

And the joy of blatting back from summer Westfield meets, with blue flames occasionally lighting up the darkness to the side of the car; I'd forgotten how much I'd missed that...  

[pete g]

poping is a sign of a weak mixture on over run

not a problem

I'd always thought popping as described was a bit of unburnt fuel igniting in the (hot) exhaust?

But I'm the first to admit I'm no mechanic....anybody have the definitive answer?

No criticism intended for original post,or Pete, I'm just interested.

thats ok

i have a wide band indicator display and pops and bangs always happen when the mixture goes weak

have said that it is the unburn fuel in exhaust banging due to maybe the correct fuel air ratio and heat

air leaks in the exhaust also make this worse.

if you have fuel injection it can be engineered it out by adding fuel at closed throttle higher rpm .i believe but i could be talking a load of bull  

[adamnreeves]

poping is a sign of a weak mixture on over run

not a problem

I'd always thought popping as described was a bit of unburnt fuel igniting in the (hot) exhaust?

But I'm the first to admit I'm no mechanic....anybody have the definitive answer?

No criticism intended for original post,or Pete, I'm just interested.

thats ok

i have a wide band indicator display and pops and bangs always happen when the mixture goes weak

have said that it is the unburn fuel in exhaust banging due to maybe the correct fuel air ratio and heat

air leaks in the exhaust also make this worse.

if you have fuel injection it can be engineered it out by adding fuel at closed throttle higher rpm .i believe but i could be talking a load of bull  

Not at all. Poping is due to weak mixture which because its too lean doesnt get burnt then makes it way to the exaust and burns there instead. When my car was tuned at NMS, Troy added more fuel. The problem with cutting fuel on overrun when you have to get back on the gas there's a hesitation, not ideal when braking hard into a corner then immediately back on the gas off the apex.

[Doug Dastardly]

So everybody's right! I'll sleep well tonight now.

[fatbaldbloke]

As said above, popping occurs when the mixture is too weak to combust and fuel accumulates in the exhaust and burns there.  It happens especially if the ECU is programmed to use fuel cut off on overrun.  In terms of performance you will get slightly better pickup if you can keep combustion going at an AFR of around 16:1 on overrun.

[Tigger]

.......... but i could be talking a load of bull  

Nothing new there then

You don't half set yourself up for these sometimes Pete

[Guest]

some just pop and produce a huge flame ....... even when just a normal carbed engine