"Snap, Crackle, Pop" exhaust mutterings on 914-4, My car's Monza-style exhaust has a tendency to 'pop' and backfire mildly that perplexes me. Options

[Jezibel]

G'day fellow 914 masochists (I'm just kidding; it's all part of the joy of owning 914s!)

I have a minor problem that perplexes me (perhaps excessively). My car is a 914-4, 74 model, that has undergone an engine rebuild and conversion from FI to cabs (Weber 40-IDF dual throats). I strongly suspect that when the engine was rebuilt, its displacement was increased (with the addition of appropriate pistons/sleeves, etc.) from the original 1.8 liters to 2.0 liters (or thereabouts). There is, unfortunately, no paper trail to clue me in on this, since the previous owner left no documentation for me on the car (he passed away) or what has been done to it.

The problem in reference is the car's tendency to experience minor exhaust 'popping' and backfiring on occasion (well after after warm-up and usually when accelerating to cruise). Not at idle.

The engine was tuned at my local Porsche shop very recently, but given this glitch, I wonder as to whether 1) the car may need re-jetting...or whether the problem in reference is due to timing issues. As I said, the exhaust is an after-market 'Monza' style system with two dual-pipes in the Monza manner.


I don't know what the present idle or main jet sizes are in the dual Weber IDF 40 carbs, but I suspect that perhaps the combustion is a bit on on the lean side...a status quo that would possibly cause such symptoms as those described, from what I have gathered from others.

One other question is: If the engine has indeed been up-sized to 2 liters, would the ignition timing still be the same as for a stock 1.8 liter?

I am well aware that the best solution to this problem would be another trip to my Porsche specialist ($ka-ching-$ka-ching) to specifically address this issue but I thought I'd ask around for any ideas that might be...as Joe Biden put it..."top of mind", that may bear on something like this.

[VaccaRabite]

Ugh! Get that wrap off your exhaust pipes. Horrid nasty stuff.

You likely have an exhaust leak somewhere. Maybe at the head, maybe a crack under all that wrap. Lets fresh air into your exhaust which mixes with the hot unburned gas and BOOM. You have your after fire pops and crackles.

Zach