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Old 05-17-2012, 07:34 AM
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Blown 383 exhaust backfire ?

I 'm new to this board and would like to say hello too everyone . I have a 73' vega wagon with a 383 blower motor that is backfiring thru the exhaust periodicly . It seems be doin it after it gets warmed up real good . or after 15-20 miles it will do it once or twice ? temp is running 160 to 190 @ these times when it does it . I have the AFR 195 competition heads with the 2 750 double pumper holley's 671 weiand blower # 1036 . The carbs are jetted fairly fat for our sea level if this helps . Any help or advise would be greatly apprieciated . I have ran dirt modifieds for years , and several years of drag boats but I've never had any dealins with a blower motor ! Thanks Kenny

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Old 05-17-2012, 09:44 AM
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Its most likely you have a ignition fault.

Start with a engine compression test and then look at the ignition system.

Possible valve spring.

If you want to dial in the blower carbs better get a AFR gauge to help show you the way. If the idle and part throttle cruise (no boost) is set up too fat the plugs will soon foul from street driving.

just remember you need to keep it quite rich when at WOT under boost.
10:1 to 12.5:1 afr.

Many competition drag only blower carbs are set up for WOT only with not much consideration for street driving, idling and part throttle operation.
But you can fix that with specific tuning and a AFR meter/gauge and a vacuum gauge will help a lot.

Does these blower carbs have power valves?
Some drag only blower carbs have the power valve eliminated.
You want functional (and boost referenced) power valves for street driving on a supercharged motor.
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Old 05-17-2012, 11:46 AM
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You're not hitting the rev limiter chip are you? That happened to me before I figured it out when I first built mine. Things were happening so fast between first and second shifts coming up so quickly, I didn't realize it, unburned fuel in the headers when the limiter started interruption.
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Old 05-17-2012, 11:47 AM
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Power valve ?

I will look at the when I get home tonight at the carbs for power valve ! Thanks for the info . Does jegs or summit sell a afr gauge ? I'm just cruzing 2 rpms and 50 mph just holding it steady ! And she will pop out the exhaust . Not getting on it at all , she runs perfect when it's to the floor !

Last edited by badvega; 05-17-2012 at 11:52 AM.
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Old 05-17-2012, 01:20 PM
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are you 100% on the firing order? I had a buddies foxbody do the same thing.. it was na but very randomly you could hear a backfire out the one exhaust and it ran fine besides that.. found out two cylinders were swapped and i believe the two ended up being 90* apart on the firing order so it wasn't very noticable
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Old 05-17-2012, 01:34 PM
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Firing Order ?

I'll check that too ,but almost positive it's right ! But you never know , I'll look ! Thanks . . . . .
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