Fire in the exit of exhaust

[christophe37]

Hi,

(sorry for my bad english)

I have a lot lof "fire" in the exit to my exhaust.

How make less ?

Regards,

Christophe

[christopher storey]

Do you mean that you can see flames in the tailpipes ? If so, there is something seriously wrong > or is it just that you can see a lot of vapour when the engine first runs? If so, this is very common - it takes many minutes of running under load to warm the exhaust system so as to eliminate this

[christophe37]

i see a lot of flames in the tailpipes

[PeterCrespin]

More information please. Noises with the flames? How soon do the flames start? How long do the flames last? Smoke before flames? Constant flames? Just on acceleration? On slowing down?

Since no normal car has flames in the tailpipes it sounds like you have mixed up some of your 12 plug wires and unburnt fuel is entering the exhaust to be burned there. Check your firing order and plug leads and spark plugs.

Pete

[Heuer]

Feel free to post in your native tongue. We can take care of the translation and maybe offer more help. There are Forum members here with many language skills.

[christophe37]

Hi,

Please help me for change carburation...

Spv, aidez moi ? r?gler mieux la carburation (4 carbus HS6 neufs).

Je pense qu'elle est trop "riche"

Merci par avance,

Christophe

[PeterCrespin]

Je pense qu'elle est trop "riche"

Merci par avance,

Christophe

Il faut toujours travailler logiquement, n'importe quelle probleme ou langue, n'est-ce pas? Donc vous avez besoin de l'esprit de Voltaire et un manuel d'atelier.

Un moteur de douze cylindres est d?j? assez compliqu?e sans perdre de vue et changer vos questions. Vous n'avez ni repondu aux questions supplementaires ni fourni encore des infos. Cependant, trop de carburant rend fum?e noire - il ne fera pas de flammes dans l'echappement. Avez-vous v?rifi? la s?quence de connexions de distributeur?

I can't help if you just change questions instead of answering earlier ones. Today I will drive from Orleans to Le Touquet and tomorrow Calais. I don't suppose you are in north west France to look at your car?

Amicalement
Pete

[christophe37]

Hello Pete,
Thanks for youre answer. I live near Tours / Saumur and you go to my home when you whant ;-)

Sorry, i not see youre fisrt answer !


Bruits avec les flammes?
oui, "boum"

Combien de temps les flammes ne commencent?
Je ne sais pas

Combien de temps durent les flammes?
Quelques secondes


Fumer avant flammes?
Non, je n'ai rien vu

Flammes constante?
Non, explosion

Juste sur l'acc?l?ration?
Non ? la d?cel?ration

Le ralentissement?
oui

Comme aucune voiture normale a flammes dans les tuyaux d'?chappement On dirait que vous avez m?lang? certains de vos fils de bougie 12 et carburant non br?l? p?n?tre dans l'?chappement pour y ?tre br?l?. V?rifiez votre ordre de tir et branchez prospects et les bougies.
j'ai v?rifi? et je ne vois rien d'anormal (mais je ne suis pas un "expert"

[Sjmmarsh]

It sounds like it is backfiring on overrun - it can be caused by using lower octane fuel - do you use 97+ RON?

Other causes include - a camshaft giving more valve overlap that slow revs can deal with, low octane fuel, engine carboned up, throttle butterfly sticking slightly open, SU piston sluggish, Stromberg diaphram split, valves not seating, or exhaust leak at the manfold, take your pick.

I'd look at manifold leaks and the diaphragm if better fuel doesn't clear it.

Steve

[christopher storey]

I'm afraid I cannot see any possible connection between fuel grade and this problem . Nor can I see how an exhaust manifold leak would cause this, unless it is being suggested that it is operating as some kind of air injection system , but even then it would require unburnt fuel in the manifold . The first thing I would look for is excessively retarded ignition timing which can allow unburnt mixture to pass into the exhaust in significant quantities

[malcolm]

I had this issue with another vehicle, where it turned out to be a damaged exhaust valve allowing fuel into the exhaust system on the compression stroke. I think this sounds like a head off issue (not carburration) unless it is sorted out by timing.

[Sjmmarsh]

Christopher

Backfiring needs unburnt fuel and air in the exhaust system to ignite, so leaks in the manifold or exhaust are a mechanism that allows the air in.

If the car is set up for high octane fuel then using low octane fuel can cause pinking that can result in unburnt fuel getting into the exhaust.

The problem is that there are potentially many things that could lead to this problem. On some cars flames are seen as a desirable feature!

Steve

[PeterCrespin]

Christopher

Backfiring needs unburnt fuel and air in the exhaust system to ignite, so leaks in the manifold or exhaust are a mechanism that allows the air in.

If the car is set up for high octane fuel then using low octane fuel can cause pinking that can result in unburnt fuel getting into the exhaust.

The problem is that there are potentially many things that could lead to this problem. On some cars flames are seen as a desirable feature!

Steve

I am with Christopher and recognise zero connection between fuel grade and backfiring, pinking and unburnt fuel, or some of your other theories, sorry. I do agree that an air leak in an exhaust can cause popping on the overrun and weak mixture from a split Strangleberg diaphragm can do similar things. On the other hand it could be rich mixture from one carb with a stuck float pouring fuel in.... Being a four-carburettor engine it is auite feasible for it to run on nine or even six and with an exhaust balance pipe as standard the symptoms might appear from both bank tail pipes.

If the engine has been worked on recently my bet would still be mixed HT leads, although there are so many vacuum connections it would be a'anifold leak PLUS a flooding carb maybe.

I wouldn't go anywhere near lifting a head until many more issues are clarified.

Christophe: did the car run OK and thrn this problem began without you changing anything? Or has it never run correctly and you or your mechanic have worked on the car? Is it American emissions equipped or European with no air injection?

Pete

[MarekH]

The situation is relatively simple. There is unburnt fuel in the exhaust. It got there through one or more of the cylinders because it didn't burn inside the cylinders like it is supposed to. (This means the air which was pulled into the cylinders has also passed straight through into the exhaust - no need to chase "leaks" to find "air" in the exhaust.)

There are only a couple of reasons which can cause this:-
1/ The wrong amount of fuel got in in the first place into one or more cylinders and it has gone straight through - if it is outside of a ratio of about 9:1 to 17:1 (air:fuel) then it won't want to ignite;
2/ The combustion is either retarded too much or non existant in one or more cylinders. If combustion is retarded, it is still going on long after it should have finished, i.e. it is burning in the exhaust. If one or more plugs aren't firing, then looking at the colouring or soot or damp fuel on the plugs should reveal where the problem is.

Backfiring on decelleration is not uncommon. A lot of engine designs have a valve to admit extra air when they detect that throttle has been snapped shut. On your carburettors, these are called throttle bypass valves and their diaphragms may be clogged or brittle and broken if the carburettors are in need of servicing.

The quality of the fuel is of no consequence - you can burn high or low octane petrol or even lpg and simply adjust the timing to compensate for the speed of combustion.

kind regards
Marek