new exhaust backfiring

[DirtDonk]

That will never be enough in your case. Sure, if the over-lean mixture issue was extremely minor, you might see a difference. But those screws are for idle only, and have an absolutely minuscule effect on overall jetting.

In the case of "too much" it's only too much once your idle suffers. Richer or leaner, at some point it won't idle correctly and you'll have to re-adjust them to compensate.
Set them for the idle and leave them until you change the main jets. Then you'll likely have to re-adjust them to the new parameters.

A new free-breathing exhaust is way more of a change than idle screws could ever compensate for.
Especially if you were already borderline lean to begin with.

Paul

 

[Joe473]

That will never be enough in your case. Sure, if the over-lean mixture issue was extremely minor, you might see a difference. But those screws are for idle only, and have an absolutely minuscule effect on overall jetting.

In the case of "too much" it's only too much once your idle suffers. Richer or leaner, at some point it won't idle correctly and you'll have to re-adjust them to compensate.
Set them for the idle and leave them until you change the main jets. Then you'll likely have to re-adjust them to the new parameters.

A new free-breathing exhaust is way more of a change than idle screws could ever compensate for.
Especially if you were already borderline lean to begin with.

Paul

A different pcv may give enough. I had some issues with pcv valves not transitioning back to idle and tried a few. Had a Chevy one in during winter that worked great but gave me lots of popping on decel!

Sent from my SM-G960U using Tapatalk

 

[DirtDonk]

Good point. We don't even know if tommyg has a PCV setup to begin with.
So what else has been done to the engine Tommy? Any other mods? Stock original, or something else?

We had discussions about different PCV valves and how they act over the years. Some of us even keep a different one in our tool boxes for when we go to higher altitudes and want to lean things out a bit.
In my case, the Chevy version worked for me at sea level and the Ford one (different model though) was the one that made things super lean.

Got any pics of the engine compartment anyway tommyg? Be fun to see what you're working on, even if it doesn't help solve the puzzle.

Thanks

Paul

 

[tommyg]

Thanks guys. I'll definitely take a pic of the engine compartment tomorrow, it looks as stock as they come for a CA '74. Going to try to take off the smog pump belt next just to see if that makes a difference.

 

[tommyg]

Here is the engine bay and smog pump area. Going to go ahead and try changing the valves...

 

[tommyg]

take two...

 

[tommyg]

Also, am I missing anything here?

 

[DirtDonk]

Only one pic came through for me. I can see the early Dura Spark distributor, PCV valve, power steering cooler, heater hose and half the carburetor with stock air cleaner.

The manufacturers were experimenting with leaner-than-before air/fuel mixture ratios, and air pumps (since '66 actually) and different ignition timing advance curves, and such like that.
If it ran well before with the air pump connected, nothing says you can't re-configure the fuel mix to work with it again.
Because it's a '74 you don't "need" to keep the air pump intact because you don't get the bi-annual inspections. But know that as soon as it's disconnected, if you leave it that way for very long you might as well toss it because it will freeze up solid within a few months. Rendering it unusable in the future.
The only downside of that for you is that it will be harder to sell your Bronco to someone that lives with inspections, or just wants all the stock stuff intact.

Paul

 

[tommyg]

thanks Paul. Weird because I posted the pics, then they somehow disappeared. Posted them again, and they disappeared again. Going to try to replace the PCV valves, and if that doesn't work I will likely remove it all.

 

[DirtDonk]

Why change the PCV valve? Most likely you'll just make it even leaner if you try to find a different one that's more "compatible" with your over-breathing exhaust.
Besides, you can remove all the other stuff if you want, but you're not going to de-lean it that way. And likely might make it run worse.
Although, I suppose if it gets rid of the popping by getting rid of the pump, you'll have a win and can leave it that way.
But don't ever remove or defeat the purpose of a PCV system. Yes, it might be a "smog" item, but it was one of the best things to ever hit the automotive world too.
So leave at least that.

Did you check for exhaust leaks? Remember the suggestion of one causing the popping? Or was that in another thread? I can't remember at the moment.
Did you try "plugging" the PCV valve temporarily to hopefully richen things up? Again, only temporarily, but it's in the way of a test to see if it helps and how much richer you have to go.

While you're on the subject of pics, can you try to post the others again?
What website are you using to host the images by the way?

Thanks

Paul

 

[tommyg]

yeah, the PCV valve had no effect. I'm taking it back to the muffler shop tomorrow.

 

[tommyg]

try one more time, from tinypic...

 

[DirtDonk]

That worked! And yep, about as stock as they get too.
For sure take a lot of images of the under-hood stuff for your archive if you decide to remove all of that stuff.
And if you do, remember that there are probably several members looking for that kind of stuff for their restorations, or just to register their '76 or '77.

Paul

 

[edmedlin]

1 3 7 2 6 5 4 8 is the firing order on my 380hp 302 crate engine. This is a late 80s roller block and hefty roller cam spec'ed for bottom end torque. Like Paul said, the cam determines the firing order.