Backfire at high revs?

[shake n bake]

Hopefully someone can advise me on a small issue?
At high revs my car occasionally pops out a backfire, under hard acceleration in 2nd and 3rd, I've read these cars run lean but just want to see if the collective knowledge have the problem and solution?
It's a 97 450, all standard.

[ClassiChimi]

I'm no expert but I thought back fires were usually caused by un burnt fuel in the exhaust.
Over fuelling maybe
Cam timing effecting exhaust valve over lap
A dodgy exhaust valve or seat,
Or something far less worry some but I can't think of it.

[jojackson4]

Air leaks can do it as well

[ChilliWhizz]

I get massive bangs coming off the throttle when changing gears at around 6k rpm, sounds bloody awesome

[TV8]

ChilliWhizz said:

I get massive bangs coming off the throttle when changing gears at around 6k rpm, sounds bloody awesome

i get this as well. sometimes more massive than others but good fun what ever size the bang or pop!

http://www.pistonheads.com/gassing/topic.asp?h=0&a...

[Bluebottle]

ChilliWhizz said:

I get massive bangs coming off the throttle when changing gears at around 6k rpm, sounds bloody awesome

Mine did it a couple of years ago and blew the Y piece clean in half along the seams
I was chasing Christians LSxx Griff and momentarily hit the rev limiter

[ChilliWhizz]

Bluebottle said:

ChilliWhizz said:

I get massive bangs coming off the throttle when changing gears at around 6k rpm, sounds bloody awesome

Mine did it a couple of years ago and blew the Y piece clean in half along the seams
I was chasing Christians LSxx Griff and momentarily hit the rev limiter

This is why we love our TVR's

They bring out the hooligan in all of us

[fausTVR]

When mine started popping at high revs the coil gave up the ghost very shortly after, so was possibly causing it in the first place. New coil and no more pops.

My assumption is that with a failing coil, the spark generated at high revs is patchy so unburnt fuel gets lit when it enters the hot exhaust manifold.

[shake n bake]

It crackles and pops off throttle which is fine, but it's the in throttle bit that concerned me a bit?

[fausTVR]

I'm no expert of course but if it is coil, I would expect your plugs to be sootier than usual because of the less than perfect burn, which is causing the pops. Do you have access to an alternative coil to rule that out? I know how silly a question that is.

[Bluebottle]

shake n bake said:

It crackles and pops off throttle which is fine, but it's the in throttle bit that concerned me a bit?

Are you sure it wasn't the rev limiter? The 14CUX soft limiter chucks a load of fuel in , which the reason mine did it as the unburnt fuel ignited on the cat

[shake n bake]

Bluebottle said:

Are you sure it wasn't the rev limiter? The 14CUX soft limiter chucks a load of fuel in , which the reason mine did it as the unburnt fuel ignited on the cat

Could be, I'll try it and see if it goes further on.