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Old 12-27-2005, 07:01 PM
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429 backfiring thru carb.

I have an 83 ford bronco with a 429 and a 4 speed tranny, my problem is in 4th gear if im in town cruzing (1000 rpm) and I go to accelerate even if I ease into the throttle it pops through the carb and will keep doing so unless I back off from the gas. I dont have an accurate idea of timing currently( balancer looks slipped, it reads 23deg initial and hardly idles at 10deg) I set timing where it runs the best and it dosent have a stock cam anyway. Im running an extreme 4X4 cam 256H .514 lift int and exh. 210 int at.050 218 exh at .050 I ported and polished D3VE heads to flow 170 cfm on exh? i think thats what it was ( its been a while) and I run a holley 750 vac sec carb with an 85 power valve and blow out protection, Im running 73's primary and a stock plate rear, (carb model 3310), stock spring for the secs, and a # 32 squirter.

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Old 12-27-2005, 07:31 PM
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check and make sure all your valves are adjusted correctly... has it done this since you installed the cam... or did it just start?
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Old 12-27-2005, 07:50 PM
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try seperating your plug wires, it could be cross firing. also check your fuel pressure and volume, or restricted fuel filter , causing a lean condition. also check the carb mounting bolts, and intake manifold bolts, to see if they are loose. this can cause a lean condition also.
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Old 12-27-2005, 09:34 PM
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what dklong said could be possible too... how do you have the mixture screws set? if they're a little on the lean side then when you hit the gas it'll lean out and pop through the carb. try to back them out 1/8th - 1/4 turn and see if that helps any. And if it does then keep adjusting till you have it right. how hot does the motor run? does it run a little on the hot side or normal?
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Old 12-28-2005, 08:49 PM
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The engine runs about 5 degrees hotter this year than last, however I have switched antifreeze this year and am running a totally different valve train than last year so temp might be due to that. The engine was popping like this last year too, but on the bottom end(with the other cam), now off the line I go like crazy and if im under reving in 4th it pops when I try to rev any more. I have a gear disadvantage right now.... 3.50:1 gears with 32" tires and driving 25-35 mph, not so good, it seems much better as speed picks up at 35 i dont really notice a problem and on interstate I feel like I could floor it and just go. I am going to increase my base timing a bit, it seemed to like more initial a while back but I had a bad starter drive and so I backed off the initial to try to keep the pinion gear engaged with the fly wheel... it helped a little, new starter and its all better. I am also going with something like 4.56 gears when I get my lift on and bigger tires.. maybe more gear, I guess it depends what my final drive ratio is with 35-39" tires. I have height laws to stay under and practicality is important.... kinda... It is my winter daily driver and summer offroader. P.S. all the ignition has been replaced since last year all wiring has been replaced and the whole drive train is different, the carb has a different body and base but the same bowls and settings, My mileage this year seems much worse too.... maybe my driving isnt helping though... in granny it pops the fronts up... just way too much fun... till the 9" blows its all good.
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Old 12-28-2005, 09:06 PM
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Are you sure you don't have a vacuum leak? That would also cause your idling problem.
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Old 12-28-2005, 11:12 PM
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Doc here,

Don't overlook the possibility of a failing Coil, or ECM...Either (or both ) may give the same results...

The ECM you can test for free at the parts house..

The coil will check as follows : Measure with a DVOM set for R X 1 scale or autorange, and measure the primary side, It should read less than an ohm..

Measure the secondary side, It should read between 10,000 and 11,000 ohms on an R X 10 scale or auto range...



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Last edited by docvette; 12-28-2005 at 11:14 PM. Reason: Cuz I can.....
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Old 12-28-2005, 11:20 PM
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I had the same problem on my 400 in my 65 pickup I didn't know what it was but I found out my timing chain jumped and had a few teeth broken. Sorry for the news it may be something else, but that was the problem for me.
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Old 12-31-2005, 04:20 PM
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The module is new and I tested it when I picked it up. The coil is the third ive run since the problem started occurring, then engine has been rebuilt once since the problem first occurred( motor mount broke causing the thrust bearing to wear out) I think the distributor im running might have the same weights and springs as the other one I was running, could I have too little advance for the load i have and the high gearing? It has quite a bit of load on the engine in 4th gear at only 1000 rpm could the advance be too slow?
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Old 12-31-2005, 06:15 PM
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Doc here,

This may sound really...really basic...

Are you sure the fire order is correct? Have you actually hand over handed the wires (especially 6 and 5...) Like at least 3 times ... common overlooked problem that has this symptom..I do it all the time..

CCW , 1 3 7 2 6 5 4 8..

Number 1 at about 1 O'clock?
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Old 12-31-2005, 06:48 PM
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Try a 35 squirter in carb.
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