Re: what causes backfiring?

In message <7l1eq1dt9v78d0vldl75qcktp2048bkgb9@xxxxxxx>, Tom Woods <tomarse_@xxxxxxxxxxx> writes 
My car has started backfiring a lot today and i was wondering if
anybody could suggest what the cause might be.

It is a carbed engine and has a simple open loop gas system on. I run
it on gas only.

When it has been backfiring it blows the flexy pipe off at the air box
and sometimes pops a vacuum line out of the inlet manifold (where the
brake servo is fed from).
Whenever it pops the vacuum line off the car stalls and i have to pull
over and refit it.

I was wondering if the gromit on the vacuum line on the inlet manifold
could be the cause of the backfiring as it doesnt seal very well
anymore bacause it has perished (and half of it seems to have
disapeared down the inlet!). Or is it more likely to be something else
and the vacuum line popping out is just bacause of the backfire?

I strapped the vacuum line down as a temporary fix on my way home from
work but it still banged a few times after then and popped the flexy
pipe off the airbox.
I have ordered a new gromit but it hasnt arrived yet.

It seems a bit down on power too over how it was yesterday (when i did
a fairly long motorway drive), but that could also be because the gas
tank is fairly empty. It has never backfired when its been empty
before though.


2 causes of back fire are ignition and lean mix. If your vacuum line is open to air because of the grommet failure then it will be drawing air in to the inlet manifold below the mixer and hence weakening the mixture.

I don't think nearly empty tank will have anything to do with it. I run a V8 4.0 litre and I run my tanks right down to empty regularly and never have a problem.
--
hugh
Reply to address is valid at the time of posting
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