So while driving today (this happened twice), while downshifting, the engine started to make this weird sound as i accelerated almost like it was having trouble accelerating. The car wasn’t accelerating at its normal speed so i tried to give it gas and still averaging slower and the engine sounded groggy even when upshifting. I put it in neutral and instead of the usual 1000 RPM idle it had a hard idle at 500 RPM barely able to keep itself on. I revved the engine and some of my Weber carburetors popped and the exhaust also popped at the end. No idea why this happened twice but it was a scare the first time it happened. Any idea what it could be due to?