Backfiring on deacceleration

[Alpine James]

Hi all; Seems my car likes to 'fart' when I take my foot off the gas. Not real loud backfiring, more of a burbbling sound. Is this a symtom of timing being off? I can't check the timing with a light because the non stock (Minx) rad blocks any view at all of the timing marks.

Or is it possibly a carburation problem. One of the local 'know it alls' thinks the carbs are letting to much fuel through and it detonates in the exhaust.

Or could it be something else?

As always, you comments are most appreciated.

Thanks, James

 

[husky drvr]

James,

What is the possibility of a leak in the exhaust system?

 

[Pumpkin]

Farting?

James,

What is the possibility of a leak in the exhaust system?

This is a very definate possibility. I have the same "excuse me" it happened again

I do have an exaust leak , what happens is the de-cellaration causes "air" to be sucked into the exaust system, the excess fuels NOT burned will explode, causing the discription in the post.

Mine is soon to be fixed ,, the exaust manifold to exaust pipe is leaking. Also check for any loose intake manifold bolts. Tighten up when cold.

Take care I have blown mufflers to whoopee and even made timing chains to separate.. Not on a real car..a 72 chev pu..
My 2 p
chuck

 

[Alpine James]

Interesting; The muffler and part of the tail pipe is new, but I havn't had a real good look up the the exhaust manifold.

Perhaps this is also a symptom of my really bad gas mileage, if there is unburnt fuel. But what is the usual cause of the unburnt fuel getting into the exhaust. I guess leaky valves or misfiring plugs. Anything else?

Thanks guys

James

 

[RootesRooter]

If you have a stock exhaust manifold, check for a crack at the junction between the two middle pipes.

 

[jumpinjan]

My series I (with a 1600 engine) had an Abarth muffler (back in 1972), and it would produce the same sound. The complete exhaust system was new (all pipe from engine to muffler in rear), as well as the engine and I got 30 mpg on the highway, so its not so much carburation. You don't heard the backfiring anymore because engines are fuel injected and the fuel is shut off on deacceration.
Jan

 

[alpine_64]

Is it backfiring, or are you getting the pop and crack as the pressure builds up, as in like when you drop from 4th to 2nd and you get the rally style pop and bang with he back pressure?

A free flowing exhuats will allow this more.. sometimes you will get it when lifting off at say 2000rpm and 4000... or is it a loud backfire?

Just a question... as you said more of a burbling sound.. so i am thinking might not be an issue.. just that lovely old car.. sporty sound.

 

[Andrew]

Gurgling and Bubbling out of carbs.

My car is the same and I just chose to ignore the bubbling and burping. Running hard in 4th and then letting off and idling down into 3rd you can hear some gurgling and bubbling out of the Zenith carbs. I thought it was just the old carbs along with the old exhaust system. Mind you the front carb seems to run a little rich but I am a little afraid to even consider tackling the carbs with all of the problems that I have been having.

I can produce a wave file of my car and provide it for you to hear and you could compare your car to my car if you wish.
Let me know and I can produce some MPG video and wave files for you to watch.

 

[Jim E]

Back fire or "patching" out the carbs is typically a lean condition, the mix is just so exsplosive when it is lean that you get patching from the combustion chamber out the carbs. I had this with my 40s

 

[Jeff Scoville]

I'm just experiencing that very thing with the twin Dellorto 40's, but just got it going so haven't really set anything yet.
Three straight days of sanding and buffing.
Now to install the interior.
Anyhow, Andrew, I would guess your hearing the "normal" burbling of these wonderful automobiles.

 

[Alpine James]

If it doesn't rain tonight I will try to get a better description.
Thanks, James