[Healeys] exhaust popping

[Bob Spidell]

AFAIK, the 'popping' can only be one thing: small explosions in the exhaust system.  There can only be an explosion if 
there are three things: a combustible substance, an ignition source and oxygen (actual explosives provide their own 
oxygen, usually from oxides of nitrogen).

So, it follows there must be unburned fuel in the exhaust (duh), some oxygen--from air, this is why exhaust leaks 
contribute--and an ignition source (heat or hot spots in the system).  I suspect--don't know for a fact--the unburned 
fuel comes from the high vacuum in the intake system with closed throttles, which draws fuel from the jets even with the 
pistons down and the needles all but closing off the 'annular ring' between the needle and the jet opening.

At times, my BJ8 has not popped on decel/downhill/etc. with different exhaust systems.  Don't know why, I've kept pretty 
much the jet/mixture setting as long as I've had the car (31 years). Currently, I'm using an exhaust cobbled together 
from Ansa pipes with Heartthrob mufflers (from good ol' JC Whitney; I call it 'Frankenmuffler').  It pops a lot, 
including some pretty loud bangs with closed throttles going downhill.  I put an 'H' pipe between the pipes fore the 
front mufflers; suspect that contributes but danged if I know why.

Bob



On 10/10/2014 1:22 AM, Oudesluys wrote:
> The popping often happens on side draft carbs, no idea why. I have Dell'orto's on my car, running rather rich, and it 
> pops gloriously on the overrun.
> Listen to any 60's/70's Alfa Romeo, they all do it. If they don't there is something wrong. The same for most AH's and 
> MG's although it is less pronounced than with the Alfa's
>
> Kees Oudesluijs
>
>

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Bob Spidell           San Jose, CA            bspidell at comcast.net

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