Hi all!
Last night I put some stabil into my 1969 Etype FHC and i had backfire for the first time ever. I ran the car for about 10 minutes to get the stabil through the system (probably won't be running a ton this winter so i wanted to keep the fuel from getting gunky). After the car heated up it stopped backfiring for the most part (a couple pops when letting the choke out, but not much else, although i didn't throttle up at all at that point, so there's potential it could still have been happening). Again, i have never had the car backfire previous to last night. I assume it was just the stabil causing the mixture to be different than normal? Hopefully i didn't destroy something and not know it, I'm still pretty new to this. Thanks for the help.

Extra info: My friend and I recently changed the brake master cylinder, and he suggested that maybe one of the vacuum lines has a leak which could cause the backfire? Not sure if this is a possibility or not, but figured someone on here might know. I didn't hear any whistling, didn't think to listen closely for any hissing. The idle was 1000 rather than the normal 750 with no choke which i found slightly odd. The idle was consistent though, not fluctuating. Won't have time to start it again until at the soonest tonight. Thanks again for any help

 

Did you put fuel in after adding the Stabil ? If you didn't then it's likely it sank to the bottom of the tank and thus your engine got full strength Stabil, or at least far more concentrated than if it had been thoroughly mixed with the fuel.