Engine ‘Popping’ on overrun

[AshM]

So my car is back on the road after an engine rebuild. Delighted, going really nicely and done about 800 miles so far.

It’s a frustration not to give it some stick as it is keen to run. It’s also lovey and quiet and gives the impression of a ‘balanced and calm’ engine at tickover (that may make me sound like a madman but you will know what I mean).

My only small issue is that it is popping slightly on overrun. If using the engine to slow the car you can hear it popping slightly. Not a massive good old fashioned backfire but definitely some late explosions.

Is it simply timing?

As always, value the thoughts of the collective wisdom.

Thanks
Ash

[Heuer]

Running too rich?

[Tbob]

Check this topic on JL:

https://forums.jag-lovers.com/t/throttl ... lve/352314

I found throttle bypass valves on Stromberg carbs can contribute to this.

[abowie]

I would accept that as normal.

And at 800 miles I'd be starting to push the engine a bit too.

[H7OB]

Mine also does a bit of the same. I was concerned it might be too hot/lean but the recent time on the dyno proved otherwise. It might also be an air leak upstream on the exhaust allowing air in and igniting the unburnt fuel. My exhaust seems a tad louder / less restrictive so that might also be contributing but now I know it’s running well and fuelling correctly I quite like it!

[AshM]

Thanks all for the responses. Appreciated as always.

Will make checks based on ideas.

Paul, your reply made me think. The car is now running with a new ClassicFabs SS exhaust system and I wonder if that is giving me different noises to what I have been used to?

Thanks again.

Ash

[H7OB]

Hi Ash,
That would sound to be a likely factor. If you were previously mild steel theres also that difference.
Id just say make sure you re-jet / change needles to suit, to ensure its not too lean with the new exhaust.
A good rolling road session is always worth the money. I had just done 1000 mile when I braved it! Mine just runs beautifully now, makes great power & torque and ticks over smoother than anything!
Cheers