84 is popping/backfiring

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84 is popping/backfiring

jstone4646
My question is what would cause these 351 to pop and crack out of the exhaust like a motorcycle running no baffles?

Some information ahead of time, my truck is a straight pipe exhaust running true duals without cats and dump right in front of the rear tires.  I have not had this popping until now.

So most of you know the starting woes I had with the slow start scenario in the 84.  I have gotten that sorted out and put in the new starter so that is fine.  But at some point I found my distributor was not tightened down and it has been ever so slightly twisted (I do not have any marks between it and the manifold to determine where it was originally).  Once I got the slow start figured out I cranked it back up and noticed its popping and crackling in the exhaust.  It runs fine but just pops and backfires like a badly tuned V twin motorcycle would do.  This was not a problem before and once I found the distributor was loose I can only imagine this is the reason because of timing.  I tried twisting the distributor at about 1/8th turns left and right to see if I could find the sweet spot but no luck there either.  Twisting it too much made it worse one direction, and too much the other direction made the carb spit air/fuel.  I also hooked up a vacuum gauge and found that my motor is running around 17-18 on the vacuum gauge when I get the mixture screws at their peak.  

Is the popping just a timing problem most likely, bad carb mix, or something else going on?  Like I said it has never done this until now, and I noticed the distributor is twisted.....checked that out and found the hold down was loose so I guess it spun between Friday and now.  I have tried moving it (the distributor) as slowly as possible in both a clockwise and counter-clockwise direction while the motor is running to see if I can get it to quit, but no such luck yet.

What have I done since it was running right?
-New Starter
-New Starter relay
-New Voltage Regulator
-Found the distributor twisted clockwise more than before (based on location of the vacuum port, it use to be somewhat straight forward, but now its twisted left).
Project "Red" (not really named yet): '84 F150 4x2, Holley 4bbl 351 w/302 cam shaft and side exit pipes.  Still learning what else is there but in progress of putting her back together and on the road.
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Re: 84 is popping/backfiring

jstone4646
I bet I goofed up the firing order on cylinders 2 and 3 now that I think about it.  I had disconnected the plug wires to make room for my socket/extension under the exhaust header when pulling the old starter and putting in the new one....I bet I wrongly connected them back up.....in fact I am guessing that is probably what happened....if so I will just put my dunce hat on for a while.  More to come tomorrow.
Project "Red" (not really named yet): '84 F150 4x2, Holley 4bbl 351 w/302 cam shaft and side exit pipes.  Still learning what else is there but in progress of putting her back together and on the road.
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Re: 84 is popping/backfiring

Gary Lewis
Administrator
Boy, that would do it.  Hope that's it as that's an easy fix.
Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker in front & 10.25 Spicer/Trutrac in bac, & EEC-V MAF/SEFI
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Re: 84 is popping/backfiring

jstone4646
well update....not really a good one either.  I checked the plugs to make sure they were right and the firing order is out of whack based on the distributor cap.  Disclaimer I have not messed with it since I bought it so I dont know how this thing was even running to begin with. 1 8 4 5 and 6 were correct but instead of it finishing off with 2 7 3....it was 7 3 2.  So I am just resetting timing all together now.  Could explain the running issues I have been having since day 1....but again I dont know how the hell it was even running anywhere close to right.
Project "Red" (not really named yet): '84 F150 4x2, Holley 4bbl 351 w/302 cam shaft and side exit pipes.  Still learning what else is there but in progress of putting her back together and on the road.
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Re: 84 is popping/backfiring

Gary Lewis
Administrator
That would cause weird problems.  Hope you get it sorted, quickly.
Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker in front & 10.25 Spicer/Trutrac in bac, & EEC-V MAF/SEFI
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Re: 84 is popping/backfiring

grumpin
Ferninand was having problems with the firing order because a different cam was installed.

Thought I'd mention that.
Dane
1986 F250HD SC XLT Lariat 4x4 460 C6
1992 Bronco XLT 4x4 351W E4OD
1997 Mazda 626 LX 2.0L G25M-R
1998 Suburban LT K2500 454 4L80E
Oregon