Backfiring. What causes it and is it bad? Please

It’s over fuelling if it’s popping I’d have thought, shouldn’t do any damage, only to your wallet!

 

Always thought,backfire was due to unburnt fuel in exhaust system because of timing issues but the bottom line is that there's too much unburnt fuel so either timing or mixture.
If it's timing, it's not great for engine...if your exhaust is on its last legs, the backfire could finnish it off.

Out of curiosity, who is the garage you speak of ?

 

Garage said there is an exhaust leak, that may be the cause. I would go back to your garage with the van and ask them to show the exhaust blow.

 

Popping and banging on the overrun is usually an exhaust leak somewhere, which ties in with what the garage say. If it was idling high before, that was probably masking it. Fix the exhaust leak, and the backfire should magically disappear.

 

Same as I use....was looking for a back up garage...can't quite get the measure of Matt.....and £ 54 an hour hurts....it's nearly what a plumber, sorry heating engineer, charges!

 

When mine had a backfire, it was the advance weight in the dizzy that wasn't moving....refurbished dizzy sorted it ( Matt initially missed it .)
I have a slight popping on tickover but I'm advised that is a slight leak in the exhaust system.

 

I had backfiring which was due to overfueling, I had to fit a fuel regulator now the backfire is no more, what carbs do you have Alex?

 

Was this personal...or on the van...?

 

The problem with the Sheffield ring road ..
is all the dippy students constantly pressing the pedestrian crossing buttons and halting the traffic..
They need under passes...

 

Probably a dodgy kebab or possibly a curry.

 

Alex with the handle of a screw driver tap the body of the float chambers if the back fire disappears then you probably have warn needle valves, if your carbs are Weber 34 icts they need a very low fuel supply of no more than 2psi, most low pressure fuel pumps supply fuel at 3.5 psi which is too high and will eventually wear the needle valves, my money is on the above especially if the backfiring has only recently started

 

Dirty , inside that is or cracked dizzy cap too. Exhaust system leak is a common cause, port gaskets the whole lot.

 

When your engine is idling properly, it's not pulling air through the idle jet, just the idle mixture screw. If your engine is idling high, it draws air / fuel through the idle jet, which changes the mixture.

Backfiring is essentially just unburnt fuel igniting in the exhaust, which is made worse by an air leak in the exhaust system. Generally speaking, the worse the problem, the nearer to the heads the leak is. Usual suspects are where the heat exchangers bolt up to the head, and exchanger to silencer joints. Check for tell tale signs of soot, or poke your ears at the joints with the engine running