Lot's of popping and cracking on deceleration...

[71C10SWB]

I've got my '71 swb back on the road and I like everything except all the noise it makes when I'm decelerating.
I get a lot of cackling, popping and backfiring, especially going down a big hill.

Before I give you the set-up, I want to say, I didn't set this up.
It has:
350, Powerglide, 6-cylinder gears, hooker headers, single plane Weiand intake (high rise), Edelbrock carb (cfm unknown), glass packs and full length 2.5" exhuast.

Is it the glass-packs, the engine set-up or just the nature of the beast?

What would help? Turbo mufflers? Flowmaster mufflers? Crossover pipe?
could timing have anything to do with it? I've put a light on this thing, who knows where it's set at. I've not been really impressed with the carb either (it might just need a rebuild.)

Any feedback would help.

[ZombieWeinerDog]

Originally Posted by CutlassSMan

I've got my '71 swb back on the road and I like everything except all the noise it makes when I'm decelerating.
I get a lot of cackling, popping and backfiring, especially going down a big hill.

Before I give you the set-up, I want to say, I didn't set this up.
It has:
350, Powerglide, 6-cylinder gears, hooker headers, single plane Weiand intake (high rise), Edelbrock carb (cfm unknown), glass packs and full length 2.5" exhuast.

Is it the glass-packs, the engine set-up or just the nature of the beast?

What would help? Turbo mufflers? Flowmaster mufflers? Crossover pipe?
could timing have anything to do with it? I've put a light on this thing, who knows where it's set at. I've not been really impressed with the carb either (it might just need a rebuild.)

Any feedback would help.

i would imagine its more the glasspacks. my flowmasters crack and pop a little during deceleration, but it sounds nice. i have the same setup, original 3 speed. mine does not alot at all though

[clos69]

I just put flowmasters in my blazer this past Monday and it does the same thing....

[ZombieWeinerDog]

i think a crossover pipe would help, there was just a thread about them

[smoky02]

Does it only do it while driving? Or if you rev it up does it do it on deceleration then too? If it does pop real bad, it could be one of the valves in your heads not seating. I had that problem with an 88 Chevy truck I used to drive.

[lilred67]

put an h pipe in your exhaust system it will take alot of the popping out of it. a possible reason your engine is doing it alot is a lean mixture at idle. there is not much fuel in the cylinder coasting a long way causing the the popping.... might could richen your idle fuel mixture a little to help it..

[nsuengineer06]

That's a easy one! Burnt exhaust valves. I've got a 84 1 ton w/454 that does the same thing. Your exhaust valves aren't seating all the way as stated by smoky02 above.

[OhioDan]

I always heard from my grand-dad, that it was from sucking cold air back into the muffler, allowing the unburned fuel to burn in the muffler causing the popping and cracking. Does you exhaust stop after the muffler? Might look into putting a short extension after the muffler?

[Camper Power]

what is your vacume advance running on, ported or manifold? cause my truck used to pop and backfire when decelerating when i ran ported vacume advance, now that its on manifold it doesnt pop at all.

[Willys47]

My guess is a miss firing making it pop a good ignition system would spark up the fuel mixture in the cylinder, have it burn in the exhast and making all that noise is such a waist of good fuel.

[Stocker]

While the type of mufflers can make it more noticeable, I doubt that's the cause. I would say it's something in the engine (timing, valves) or fuel delivery (carb).

I had glasspacks on my truck for many years and never heard anything like it. Last year, with new Magnaflows, I noticed a bit of snapping & popping on slow downhills while loaded with firewood.

[lost wages]

on my truck when it starts to pop and cackle it means i have loose header bolts. I have the ball and socket collectors and bolts are always falling out of them.

[WorkinLonghorn]

^^^ Bingo.