On Tue, 16 Jan 1996, Todd Mullins wrote:
> New question: Backfiring. I don't quite understand it. My exhaust
> makes a raspy, popping sound upon overrun. I had assumed that it was
> unburnt fuel travelling through the pipe and exploding when it
> encountered the outside air. Others have told me that backfiring is due
> to a lean mixture. Which is right? I believe my carbs (dual HIF4s) are
Both. Rich mixture tends to pop out the tailpipe, while lean pops back
through the carbs. I call the latter "frontfire", although nobody else
I'm not sure about the bit of it traveling all through the tailpipe
before exploding, I think it happens when raw fuel hits the hot exhaust
manifold. But I've been wrong before.
> valve is operative, I can't think of anything else that might cause
> backfiring (I have solid throttle plates). Any gurus? Denise?
Well, the reason those silly buttons were put on the throttle
plates was to prevent overly rich mixture on trailing throttle. Aha! I
must say though that I have replaced my plates with solid ones and have
no backfiring problem (frontfire while the engine is cold, oh yes).
John M. Trindle | firstname.lastname@example.org | Tidewater Sports Car Club
'73 MGB DSP | '69 Spitfire E Stock | '88 RX-7 C Stock