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Discussion Starter #1
In my 82, I just completed installing a rebuilt 351 from a 1978 Ford Van. I previously had a 302.

Tried to fire it up this morning, and it fired right up, but it has an intermitant pop coming out of the carb...It is firly constant, but not constant enough to define a pattern. It does run, put very rough and stuff comes popping out of the carb.

I have set the timing to about 8 degrees btc, and the dizzy is in correct - i rotated it 180 and it would not fire....Put it back to where it was (and made sure it was on a compression stroke w/ my finger over the plug hole) and it fired up again, but w/ the popping out of the carb...

The motor was rebuilt by a guy and I got all of the paperwork on it from the machine work and such, and I got a heck of a deal on it. However, I am thinking something was not put back together correctly.

Ideas???? Could the cam timing be off?? Or, what else? How would I go about checking the lifters to make sure one of the valves is not opening too far?
 

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Discussion Starter #3
I checked the spark plug wires 1/2 a dozentimes.....going clockwise on the dizzy cap, and 1-4 on passanger, 5-8 on driver front to back

1,3,7,2,6,5,4,8
 

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I thought the firing order went COUNTER clockwise. Try setting the timing to 10* BTDC. Make sure you have no vacuum leaks and that your plug wires are good too.
 

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I would suspect the cam (worn or not timed correct)or lifters (not adjusted right), It sounds like the intake is opening when there is compression in the cylinder. I know this wll happen when the cam is worn.
 

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As I recall, most, if not all carb backfires are connected to IGNITION related issues: timing, plugs, plug wires and firing order as previously stated.

If you had a backfire from the tailpipe, MECHANICAL related: ill-adjusted valves-rocker arm, worn cam lobe, timing chain/gears, burnt valve.

Can you attach a vacuum gauge and give us a reading??
 

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Try 10º btdc as previously stated. I had the same issue after installing my newly rebuilt 351W and finally figured it out. I just kept switching plug wires either one plug clockwise or one plug counterclockwise until finally I got it all lined up right it ran perfect. I don't know how it got off but it did, just try moving all the wires one over in each direction and see what happens.
 

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osubroncoman said:
I checked the spark plug wires 1/2 a dozentimes.....going clockwise on the dizzy cap, and 1-4 on passanger, 5-8 on driver front to back

1,3,7,2,6,5,4,8
Distributor rotates counterclockwise.
Hows the vacuum?
 

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Discussion Starter #10
I meant to say counter clock wize on my previous post... A little more detail from me might help on this....

I am actually getting a spit-back through the carb, leading me to belive an intake valve is hanging open..the cam in the truck is new, stock grind. I am assuming that if the cam timing were off a few degrees, I would get spit back thru the carb like I am expereincing?

I will pull the vaccum this week and post back....
 

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You know, there should be an alignment marking on both the CAMSHAFT gear and CRANKSHAFT gear, that aide you in the proper timing/alignment of the camshaft. Can you/did you verify this was the case, prior to closing up the engine??

Based on your writings, it sounds like a minor problem. Hit us back after you attach the vacuum gauge.

~Rudi~
 

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what type of carb do you have, the holley carbs i have heard of doing this. there is a blow off valve in them. other than that iam at a loss never heard of it doing that only at idle.
 

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osubroncoman said:
It is an edelbrock 1406, it was on my 302 and ran just fine before I started the swap about 1.5 months ago.
might be a little lean for a 351, which would cause it to backfire. I would suggest adjusting the idle circuit. It may require upping the jet sizes. Check the color of your plugs, they should be light brown at the tip (for idle).
I cant help you on an edelbrock, I do Holleys
 

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Discussion Starter #19
haven't had it running long enuf to get the plugs dirty....

the cam is a new, stock grind and came w/ the rebuild kit the guy bought...

I am planning on installin an 02 sensor and a lean/rich gauge to dial in the carb to 14.7, but the popping scares me to the point where the truck has not ran for more than about 30 or so seconds at various points on Sunday, about 6 times..

the 1406 seemed a little rich for the 302, so I figured it would be about right for the 351...if not, I can re-jet it and I was planning on rebuilding it anyways since it is a few years old, but I was going to do that after it got up and running..
 
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