What made my backfire disappear?

Hi all,

When I first got my '71 911E (with Webers) in March, it would backfire pretty regularly. If you coasted along for a bit and then returned to throttle, there would be a small pop. Definitely audible, but nothing too serious.

Since that time, I've replaced both the regulator and the alternator and also changed the oil and filter.

Lately, I've noticed that it rarely backfires anymore, even under the same coast-to-throttle conditions that used to guarantee a backfire.

Any ideas on what may have caused it to go away? I do drive it more regularly than the PO (who only took it to the track). I know you should never look a gift horse in the mouth - but I was just curious.

thanks!

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'71 911E with Webers
Golden Gate Region PCA

I'm not sure that this applies to your situation however I just had the same problem with a 944. I found that because the car had been sitting for an extended period of time the varnish build up on the valves kept them from closing causing a backfire and loss of power. I ran some Berrymans fuel injector cleaner through tow tanks of gas and not only has the problem resolved itself, but I've restored the power. Again I don't know if this is your sitution but it's something to think about.

Tim

I think you're probably right. P-cars hate just sitting around in the garage, I guess...

My 71 with Zeniths pops when you get back on the gas too. It is definitely worse after prolonged periods in the garage. I'm sure its related to sludge forming in the carbs. It clears up after steady use, and techron speeds up the process. Every mechanic I've ever spoken to says DRIVE IT!

I have wondered if it is worth pulling the float bowl drain plugs and emptying all the gas out before putting it away for the winter. Anyone ever done this ?

I drain the bowls for winter on every carburetor I've ever owned. After putting in stabilizer and running for 10 minutes.

Of course, it's a lot easier on motorcycles.

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blue
'81 SC Targa

Found with my 72 and Webers that every once in a while one of the idle jets would clog and then it would begin backfiring from time to time. Lean mixture can cause this... put a good fuel filter in the system and started using better (brand name) fuel and it went away.

JA