Backfire, popping

[1971ford]

On my '71 f250 with 429...
Within the past month i have noticed a popping. It's really only on this one hill that i live by. It's a pretty hefty hill, not small but it's not huge. When i turn at the light at the bottom of the hill and make my way up, I'll be in 2nd. Depending on how fast i want to go up this hill, It'll be doing about 2500-3000 RPM's, sometimes i leave it in second to about the 3000 point and sometimes i shift to 3rd, still going up the hill. Well at about 3,000 RPM's i'll get a slight backfire, or popping sound. It will keep popping, i will shift to 3rd if it does to see if a lower RPM cures the pop but it will still pop as i climb the hill. So maybe the RPM's have nothing to do with it. And maybe my 429 just doesn't like to be rev'd under load of climbing a hill.
I haven't noticed the pop at any other time, but this hill. The truck is always warm when i am at this hill and the pop isn't a loud backfire it is a pop that is noticable though.

I don't think it is doing any harm, and It isn't really loud but i want to know what it is. Thanks

[knightfire83]

A backfire is unburnt fuel igniting in the exhaust system.

It can be caused by a too rich or too lean condition.

Possibilities:
- Secondaries jetted to rich or opening too soon.
- Misfiring cylinder letting the unburnt fuel mixture into the exhaust stream.
- Leaking exhaust valves
- Timing (usually causes intake manifold back fires)
- Vacuum leaks
- Insufficient fuel delivery to the carb.

[OldRedFord]

Ahh..sounds like detonation maybe?

X2 on the fuel being too lean or too rich.

In the long term detonation = bad pistons.

[cdeal28078]

My bet is on the vacuum advance or the advance plate
Or timing/ignition related.
Had a 4.6 that went through plug wires about every 10k. It would start acting similar to that when they started breaking down
clint

[BobbyFord]

Is it backfiring through the exhaust or carb?

[70_F100]

If you've got popping through the carb, it's going to either be an ignition issue, lean fuel mix, or an intake valve not opening/closing properly.

It sounds very much (from your description) like an old Chevy I once owned. It had one intake lobe worn off the cam. Driving "normally", it ran just fine. However, if I got into the throttle hard or wound it up above 2500 RPM, it sounded almost like a popcorn popper under the hood.

[BobbyFord]

If you've got popping through the carb, it's going to either be an ignition issue, lean fuel mix, or an intake valve not opening/closing properly.

It sounds very much (from your description) like an old Chevy I once owned. It had one intake lobe worn off the cam. Driving "normally", it ran just fine. However, if I got into the throttle hard or wound it up above 2500 RPM, it sounded almost like a popcorn popper under the hood.

That's what I was getting at. He could have a rocker nut backing off, also.
Prolly the biggest P.O.S motor GM ever put out was the HT4100. If the sides of the block didn't rot out first, the camshaft would go flat and it was Redenbacher Central.

[michael69]

I had a 327 chevy with the same problem. When I pulled cam it had a lobe that was completly round. Never understood how it ran great when driving it normal. no skip, spit or sputter but when you got on it,it sounded like a machine gun under the hood.

[1971ford]

Thanks sounds like there arn't too many things to look for.
I popped the hood today to look at something else and i noticed that my headers are falling off . Well, they arn't falling off quite yet but i can see a slight gap between the header and the gasket, and the gasket and the head. Could this be it??

As for if it is the carb or exhaust, I don't know how i would be able to tell. It only happens while climbing that hill, not casual slow driving like around my court... I can't tell where it is coming from while in the truck. But it is a low pitched pop.
As for it being too rich or lean... the truck does run rich, maybe this is the simple problem. I need to figure out how to play with all the knobs and adjusters on my Edelbrock 750cfm carb.
As for an internal deal with the engine, thte only internal problem i have ever had (that i know of, of course) is that there is a tapping noise every once in a while. While sitting a stop light once a week i will get a tap. Like a valve or lifter

[OldRedFord]

Tighten the headers up. Did you use the supplied bolts?

[1971ford]

Tighten the headers up.

I figured that much

Did you use the supplied bolts?

Yessir

[knightfire83]

i can see a slight gap between the header and the gasket, and the gasket and the head. Could this be it??

Yes.

It only happens while climbing that hill, not casual slow driving like around my court...

"Under Load"

I can't tell where it is coming from while in the truck.

Because your headers are falling off.

I need to figure out how to play with all the knobs and adjusters on my Edelbrock 750cfm carb.

Edelbrock has online videos for such an occasion: http://www.edelbrock.com/automotive_new ... vids.shtml

[craftsman]

This same thing just happened to a friend of mine on his camaro, popped the valve cover and the rocker arm nut had backed off and the rocker arm was turned not touching anything. Tightened down the nut and it runs like a top.

[OldRedFord]

Did you get it fixed Ryan?

[1971ford]

hmm I tightened up the the header bolts, and coming home from school today i totally forgot about it, but i guess it might be gone if i wasn't reminded by the popping... because i did gas it quite a bit up that hill today. Maybe it's gone, and it was as simple as loose header bolts. If i hear it again i will let you guys know.