backfiring under de-accerlaration

[steve4063]

when i rev the car when it de-accelarates the exhaust is popping and seems to be backfiring but not a loaud bang just a popping noise.

also the exhaust seems to be very noisy generally but there's no leaks aroundf the mainfold and anywhere else that i can feel.

any ideas please

[bmcecosse]

True backfiring is caused by unburned fuel igniting in the exhaust system. Popping is possibly just a lesser degree of bfire - or could indicate an air leak with air being drawn into the exhaust system.

[Rob_Jennings]

Backfiring is unburnt fuel as has been said.

Look to your timing and check you points/coil/condenser as this is an obvious source of unburnt fuel leaving the engine.

Typically if the points are closing up you can get what you describe, although it ought to present itself when driving normally too.

[Axolotl]

You're not talking about the "farting" noise that seems to be a characteristic of the Minor exhaust are you?

Assuming not, then it could be:-

Ignition too far retarded.
Burnt / pitted exhaust valve(s) or seats.

I'd try advancing the timing a bit using the knurled knob on the distributor first, and see if that makes it any better. If not, investigate further.

[steve4063]

i would sasy it prob is more of a farting it definatley not a bank more of a pop pop

only when you rev it hard and then let the throttle of as it is nearly back to tick over it goes vroom pop pop (sorry can't write noises)

[Axolotl]

Does the noise happen while you are driving along, or when it is standing still and you rev the engine?

[stevey]

if you have a stainless steel exhaust fitted they do sound a lot louder.

[steve4063]

i don't know about driving its still under restoration at present just giving it a really good polish now and bleed the brakes then off to the mot man once i've got some money

so the popping is only revving at standstill not sure about driving as yet

[Axolotl]

Well, if you've checked the timing is about right, I'd leave it until you can get the engine properly warm and road test it to see if it is still making the noise and if there are any other symptoms.

[JimK]

Aren't you describing the noise that all Minors make on the overrun? I.e. the sound of an engine being strangled by a terrible exhaust system

[steve4063]

yes it certainly looks like it lol

i've just been playing and it now runs sweet as a nut apart from the farting out the back lol

turned the mixture knob in until it ran rough then the other way and set it in the middle advanced it a couple it turns and woo hoo perfect

oil 45/ 50 lb on tickover

red light just flickering on tickover touch the throttle and light goes off and revs nicely.

been polishing all day absolutely shattered now.

just brakes to bleed AGAIN

and mot man here i come (if your reading this please be nice )

[Axolotl]

Let us know how the MOT goes.

[DaveC]

Yes good luck with that Steve!

P.S. Suckers in post

P.P.S. did you get that revcounter fixed?

[steve4063]

P.S. Suckers in post

cheers for that dave

P.P.S. did you get that revcounter fixed? [/quote]

nope not yet and just noticed track rod end moves quite bad so rushing about trying to get one now lol

[dunketh]

Mine pops. If you're stood still and rev the engine then let off it pops on overrun. The more nutty you are with the revs the more it happens.
Also happens on the road if you 'welly it' in a low gear then let your foot straight off the accelerator.
Doesnt really happen when I'm driving properly and smoothly though.