Backfiring

[cassidyp]

My '71 backfires alot especially when the engine is cold.
1. Is that normal? popping noise even sitting there idling. Any suggestions would be appreciated.

2. Also the car tends to have a strong fuel smell in my garage, although no leaks as no marks underneath of where it is parked. Could the mixture be set too rich and causing both problems?

Engine is a 2.2 litre original with 48,000 miles on it

[azasadny]

Mine did the same thing and it turned out to be the spark plugs that were gapped too wide. I regapped the plugs to .035 and replaced the plug wires and haven't had a backfire since. Also, check all of your vacuum hoses!

[Tim Walsh]

Does it have MFI,Webers or Zenith's on it?

[Allenk]

If your running carbs, especially Zeniths, the popping when cold is common. I'm assuming it's popping through the carbs? If it still pops when warm then you are probably too lean at idle and need to adjust the appropriate barrel/cylinder. The fuel smell is more than likely a result of the popping through the carbs, since some fuel and vapor is being shot out. Is the backfire through the exhaust? Is it a true backfire or more of a popping only through the exhaust?

[cassidyp]

Guys, Sorry for the incomplete information. The carbs are Zenith's and it does seem to pop even when warmed up. Can you explain / clarify the too lean at idle and adjusting the appropriate barrel / cylinder? I think it is more of a popping through the exhaust vs true backfire.

I will check the sparkplug gap in the morning.

[Allenk]

Before adjusting anything, you should probably check timing and valve adjustment. Do a search on this topic because there are some great threads explaining troubleshooting carbs. If you are popping out from the carbs it usually means that whatever cylinder is popping, is too lean and you'll be able to tell just buy taking off the filter assembly and seeing which carb barrel is spitting. It sounds like you may have a full carb tuning ahead of you though because popping through the exhaust usually means a rich condition. So you may be lean on a barrel or two and like-wise rich on others.

Again do a search, but check timing, and points as a minimum. Is this a new problem?

[cassidyp]

I will do the search as suggested and let you know what I find. I think you are correct that some of it may be too rich / too lean

[dhoward]

Backfiring through the cabs= too lean. Popping in the exhaust = too rich or exhaust leak.

[cassidyp]

Finally got the nerve to check out my backfiring through the Zenith Carbs. Turns out what Otto recommends setting back to original setting solved the problem. PO provided documentation that carbs were rebuilt, but seems never were properly adjusted. Found that the air by pass was actually completely closed on passenger side. Haynes manual pg. 59 was there with me too. Thanks to Pelicanites that provided input, references, and gave me the confidence to attempt. Car runs much better