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  #1 (permalink)  
Old 06-06-2007, 08:19 AM
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Default Does your cobra backfire?

I have a (351) 392 stroker in my backdraft, it runs very good. every now and then it will hesitate a little. also every now and then when go through the gears and revs, if i have to back off of it, and its at 4k rpm or higher and you just let it come back down. on the way down it will back fire. is this a big deal, or is this something that is normal with a carburator? If this is normal carb function, I am going to fuel inject it, as it drives me crazy to hear my 50k car backfire like an old piece of junk.
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  #2 (permalink)  
Old 06-06-2007, 08:37 AM
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it's a function of your factory backdraft engineered, finely tuned exhaust system, guaranteed to leak where the tubes connect from the headers, underneath the hood. learn to live with it, or plan to spend a few hundred dollars to install a flange fix. there are older posts that talk about this problem.
good luck!
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Old 06-06-2007, 08:43 AM
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I would first rule out any type of exhaust leak. I had the popping noise/backfiring on deaceleration myself when I bought my car. In my case it turned out to be weber carb related. An exhaust leak can cause the same condition.

Jay
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Old 06-06-2007, 08:52 AM
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weber carb related? funny mine has a weber on it too. what did you do to the carb to fix it?
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Old 06-06-2007, 09:00 AM
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If I remember correctly it was a lean condition causing the backfiring.

Jay
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Old 06-06-2007, 09:43 AM
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Yamazee,
My BDR use to backfire when letting off the gas. Mine had slip on pipes that leaked very badly. I ended up doing a flanged upgrade not too long ago. Made all the difference. No more leaks, no more backfire at all. Well worth the time and money.

Here is the post on how I did it.
Installing Exhaust Flanges
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Old 06-06-2007, 10:04 AM
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i have fi 351 and when it back fires i know its time to put a new colector gasket in and tighten it up really tight.
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Old 06-06-2007, 10:13 AM
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Tighten all manifold bolts as mentioned. I would also check spark plugs to make sure they are not fouled.
I had backfiring problems and after cleaning the driver's side plugs and turning the curb idle screws 1/4 turn 'in' she ran like a top..
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Old 06-07-2007, 03:42 PM
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For all those running Weber carbs go to Keith Crafts forum. He talks about Cam lobe separation needing to be 14 degree or so. Webers are funny, they are usually mounted close to the port and need the right cam. Im no expert but KC has had some experience with this.
Michael
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Old 06-07-2007, 04:54 PM
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Yeah that makes sense on the Webers. Fuel injected cars also need about 114 LSA.
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Old 06-07-2007, 08:54 PM
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Some have said that this cam thing is exactly what was wrong with the backfiring.
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Old 06-07-2007, 11:01 PM
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backfiring is caused by two things happening: 1) an exhaust leak allowing oxygen into the exhaust, 2) unburned gas in the exhaust. Te two things causes a flame in the exhaust (backfire). The fixes are stop all the exhaust leaks or lean out the mixture (which could cause other problems)
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Old 06-08-2007, 06:06 AM
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By Chance could this be weather related? I get a backfire every once in a while, but only on 85+degree days. i.e when the air is warmer and less dense causing the motor to run slightly more rich. This doesn't happen in cooler weather and the engine tuner said I could afford to jet it down one step during the summer months if I wanted to as it would run slightly rich in the hot weather, but normal in the spring/fall type weather. Just a thought.
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Old 06-08-2007, 08:12 AM
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h2oman? Nice article on the flange plate install. Where did you purchase the flange plates? Those should also work on my SV. I callled SV this morning asking if they had any "flange kits" for their cars. They do not but indicated they will talk about this at a company meeting. All the slip joint cars have this exhaust leakage problem. Its annoying and needs attention about every 6 months to keep the car even remotely quiet. Thanks for a great article!!!!

Outlaw
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Old 06-08-2007, 09:19 AM
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Quote:
Originally Posted by outlaw
h2oman? Nice article on the flange plate install. Where did you purchase the flange plates? Those should also work on my SV. I callled SV this morning asking if they had any "flange kits" for their cars. They do not but indicated they will talk about this at a company meeting. All the slip joint cars have this exhaust leakage problem. Its annoying and needs attention about every 6 months to keep the car even remotely quiet. Thanks for a great article!!!!

Outlaw
Thanks.
I bought the flange kit from Bill Littleton at www.gcperf.com. I think the cost with shipping was $140. Any of the other Backdraft dealers should have them as well.

Jay at www.vintage-motorsports.com
Reg at www.backdraftparts.com
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