Wideband Readings

[gr8scott]

Seems I did pretty good tuning my carb by "feel" and "sound", but I think it could be better. It's currently set at #2, see the pic.
Secondaries are set 1 stage lean. Here's what I saw with the wideband:

@ 3000 feet, where I live:
Idling: 13's-14's
WOT, under load, going uphill - 10's
Cruising: 12's, occasional 13's

@ Sea Level:
Idling: 14's-15's
WOT, still 10's
Cruising: 13's, occasional 14's

What I found interesting was when I was heading back up the hill, half throttle, 2500 RPM. ~55MPH she held in the steady 14,s.
Stomped on it, down to 10's, backed off, back to steady 14's. Slowly worked its way back to 12's as I climbed in elevation.

I was thinking of taking it to #15 with a simple rod change, and taking the secondaries one stage leaner.

Thoughts?

EDIT: I do have my charcoal canister connected to my air cleaner, if that matters.

 

[blubuckaroo]

I use a Wideband air/fuel meter to set mine too. I also vacuum gauge on a long hose into the Bronco to see where each of the carb's circuits come into play. I found that when my cruise was around 14.5, it would balk when coming off idle. Enriching the accelerator pump didn't help it. I ended up putting in the next stiffer step-up spring.
I ended up setting it in the high 13s, but mine is at sea level.

Maybe still a little fat, but I feel it's safer for the engine.

 

[DirtDonk]

Sounds like it's taking that 10 pretty well under full throttle, but it seems to me you could benefit from trying to get it into the 11's instead. A 10 is pretty rich unless you're running a very highly stressed engine?
What is your engine setup? Stock? Slightly modified? Heavy breathing stroker?

Paul

 

[nvrstuk]

Agreed that 10's are pretty rich... charts (perfect world) show optimum power #'s in the 12's under hard acceleration.

My 460sbf under max acceleration I am seeing mid 12's. This is tuned by Garry with Moates Qtrhorse.

 

[gr8scott]

What is your engine setup? Stock? Slightly modified? Heavy breathing stroker?

Paul

Comp Cams XE256H
MSD 8479 Distributor and 6A box
Edelbrock 1905 AVS2 650 CFM carb on Edelbrock Performer intake
Trickflow 170 heads
True Duals w/ WH long tube headers
Iniitial timing 12° BTDC, any higher and I ping under load (stupid non-adjustable vacuum advance).
I have an adjustable one on order, but it's back-ordered at the moment.

 

[68rustbucket]

Comp Cams XE256H
MSD 8479 Distributor and 6A box
Edelbrock 1905 AVS2 650 CFM carb on Edelbrock Performer intake
Trickflow 170 heads
True Duals w/ WH long tube headers
Iniitial timing 12° BTDC, any higher and I ping under load (stupid non-adjustable vacuum advance).
I have an adjustable one on order, but it's back-ordered at the moment.

Have you tried running 93 octane fuel to eliminate the pinging with more advance? Also, change the springs in distributor so timing doesn’t come in too fast?

 

[gr8scott]

That's all I use, here it's 92.

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[Broncobowsher]

That's where I really like EFI, easy to tune. I set my big block up for a 14.9:1 at light cruise. 10:1 is too rich. But I can't tune a carb outside of idle mixture. I just know it needs a little leaning, don't know how to do it.

 

[DirtDonk]

Iniitial timing 12° BTDC, any higher and I ping under load (stupid non-adjustable vacuum advance).
I have an adjustable one on order, but it's back-ordered at the moment.

I agree that adjustable is better, but I don't think that is your primary issue. After all, when you're on the gas your vacuum advance is doing almost nothing. Well, other than allowing your timing to retard back down to it's mechanical-only settings.

Sometimes the vacuum advance can have an effect on this depending on just when it starts to release timing, but it's certainly not the primary mover in pinging under heavy load.

A couple of things you can do while waiting for your new part.
1. Mess with your mechanical advance as rustbucket was saying.
2. Try different vacuum sources. If you're on ported now, try full manifold. If you're already on full manifold vacuum, try ported.

When it comes to mechanical, you have three "adjustments" which are more like tweaks than adjustments. You can change the spring rates, which is your most basic tweak. You can change the advance base, which is what sets the maximum limit of mechanical advance. Or you can even change the weights themselves I believe, to have different weight values and/or profiles which also limit travel.

Depending on where it pings, how much it pings and how, or even if you can manipulate it to come and go as you modulate your throttle position at different engine speeds, you might be able to tune it out somewhat even before you try the new vacuum advance can.

It's not like 12 degrees is a bad setting though. It's actually where a lot of stock engines are happy. But if you can get a few more without the engine complaining, then by all means keep trying.
But even before that, try leaning out the mixture under certain conditions too, and then tune the timing to that.

In your case, you're so far off of the stock baseline that everything is an experiment. And it all has to work together, and unfortunately that makes you the dance master while doing the whole tuning dance.
By the way, what gear ratio and tire size is this engine trying to push around?

Good luck.

Paul

 

[gr8scott]

Thanks for the feedback guys.

Also, change the springs in distributor so timing doesn’t come in too fast?

I'll give that a shot, thanks.

2. Try different vacuum sources. If you're on ported now, try full manifold. If you're already on full manifold vacuum, try ported.

I'm on ported, but does it really matter? Once off-idle they're both exposed to full manifold vacuum.

By the way, what gear ratio and tire size is this engine trying to push around?

31x10.5's with 3.50 gears.

 

[DirtDonk]

I'm on ported, but does it really matter? Once off-idle they're both exposed to full manifold vacuum.

It can matter. At many points in the throttle they act exactly the same. But it's at idle and transition that they can act differently.
On full vacuum you might need to lower your base timing so you can get the idle speed down to a normal state. Once you plug in the hose and the timing jumps up an additional 8, 10, 15 or however many degrees your vacuum advance can add.
At this setting, your total advance actually drops just off idle.

With ported, you might start with a higher initial setting, but which still ends up less than full vacuum (usually). Once you tip in the throttle, the advance jumps up initially before coming back down as the throttle reaches higher levels.

So while they might end up the same in most situations, they can act differently under certain conditions. In other words, your results may vary.
You can perhaps achieve some advantages with one over the other, depending on the type and tune of carburetor, type and advance settings on the distributor, and individual engine (especially the way the cam is set up).

I've personally always had better luck with ported vacuum too, but I still won't ignore trying full vacuum on a new engine I'm fiddling with.
And since you're dealing with pinging under load (at some speeds only maybe?) you might try playing around with the type of vacuum you use.
There's a lot I don't know about what's going on in there though, so get second and fifth opinions for sure!;D

31x10.5's with 3.50 gears.

Should be a good combo with a strong engine pushing 'em.
Will you run a standard model trans, or an overdrive?

Paul

 

[gr8scott]

Thanks Paul, I'll play around with the vacuum source, and put some stiffer springs in to slow down the mechanical advance as rustbucket suggested.

I'm stuck at work right now and Hurricane Douglas should be here tomorrow so it might be a couple days.

I'm happy with the C4. No real use for OD here as I don't have any interstate hwys over here.

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[Broncobowsher]

Another way of thinking of the vacuum source...
If you connect to manifold vacuum idle speed tends to jump up. Say 700 to 900 RPM. If you turn that 900 down to 700 it will idle fine. But with an automatic when you shift into gear you put a load on the engine. Vacuum drops off, idle speed drops. Low idle speed is less vacuum and the further lowers the idle speed. Now you can't get a good idle in park and in gear. If the timing doesn't change (ported vacuum) the drop in idle speed is minimal.

Not just automatics, stick shift as well. Start engaging the clutch, load the engine, idle drops. At the worst time. You need more throttle to get it rolling off the line. Makes for poor drivability. With a little more throttle and ported vacuum to achieve the same idle speed you have better idle torque. Stronger and more predictable.

There are some oddities, but the above is generally the case.

 

[gr8scott]

Thanks Brocobowsher, all good points and makes complete sense. I do have excellent drivability using ported vacuum so I think I'll leave it there.

I did manage to change my advance springs yesterday after work. Here's the curve I chose. Wish I could test drive it, but alas, Douglas is bearing down.

 

[gr8scott]

So I found a jet/rod/spring combo I think I can live with. WOT 12's, cruising 13's-14's.

So I think I mis-characterized my pinging under load. It's more of a light throttle ping, like accelerating from a stop. And yes Paul,
I can manipulate it with the throttle. So like a dummy, when I got my distributor, I put the two lightest springs in thinking I
wanted my timing all-in faster. Big mistake. I was adding 21° of timing at 1500 rpm, according to the chart.

So the other day I put 1 heavy silver and 1 blue spring in, that took all of 5 minutes. I then bumped my initial back to 14°.
The engine felt strong, and sounded perfect. I thought I fixed it. Nope. The light throttle ping showed up today while cruising
around town. So after getting some lunch, I took my timing back to 12. Right there in the parking lot, people looked at me
like I was crazy . The pinging was still there, barely audible, but still there. By the time I got home, the engine sounded perfect
again. I know it's not engine temp related, as it runs on the cooler side, never got above 185. Doesn't help that the non-adjustable
vacuum advance can add up to 20°, according to MSD. Hopefully I can tune it out with the adjustable one I have on order.
Maybe I'll go for a drive with the vacuum advance disconnected and see what happens.

 

[blubuckaroo]

I thought all vacuum advances were adjustable.?:?

 

[nvrstuk]

Sounds like you are much closer. Try this. When the engine is cold- hasnt been run yet that day. Start it up and immediately go for a ride listening for the ping. If its not there then you know its heat related - not over heated, just operating temp.

If it's gone when cold then you can:

1- keep trying to pull more advance out

2- run a tank of 91 octane in it and see if its cured

3- something we haven't addressed is potential carbon buildup on the pistons and it's potentially and commonly doing 2 things.
- raised compression ratyio over stock so now you are getting preignition
‐ the carbon heats up and preignites your fuel causing pre-ignition

How many miles on this engine? Always carbed? Burn any oil at all?

You can get rid of the carbon easily using the tried and true water method.

Try checking a couple more things. You cant always get rid of pinging by removing an "acceptable" amount of timing.

Carbon, compr ratio, higher octane gas needed, etc

On my 418 stroker I built I had to run premium gas in the warmer weather. No ping when 70F or colder (rough guess) but very niticeable at 90F. I am SEFI, EDIS and we were pulling and adding timing here and there. 9.48 static CR with a very "tight" cam..

Good luck

 

[gr8scott]

I thought all vacuum advances were adjustable.?:?

Not this one. Don't know what MSD was thinking...

Sounds like you are much closer. Try this. When the engine is cold- hasnt been run yet that day. Start it up and immediately go for a ride listening for the ping. If its not there then you know its heat related - not over heated, just operating temp.

That's exactly what it does, no ping when engine is cold.

If it's gone when cold then you can:

1- keep trying to pull more advance out

I think the adjustable vacuum advance will help with this...

2- run a tank of 91 octane in it and see if its cured

That's all I ever run...anything else and it runs like crap...

How many miles on this engine? Always carbed? Burn any oil at all?

~80K, always carbed, never burned any oil.

You can get rid of the carbon easily using the tried and true water method.

I'll have to give this a shot.

 

[DirtDonk]

So it's not under load, but when cruising that it happens. Well then maybe the 13-14 readings are too lean for your combination after all.
But to rule that out, maybe try one tank-full of octane booster to see if it reduces or goes away.
If it does go away, then you at least know you're on the right track. If it does not, then more drastic measures are needed.

Are there any metering springs left that are slightly stiffer than the ones you're running? This would keep the metering rods on the rich steps slightly longer. Or...

Or, it's not pinging, but is something else.
I don't remember if you said, but does it have headers? Maybe you're just hearing the tinny sound of the headers. Or worse still have some leaks in the gaskets. Both have been known to sound like a light pinging/ringing sound, and yes can be even more pronounced under light throttle.
In a Bronco the two events might be harder to tell apart.

Paul

 

[gr8scott]

Hey Paul, I do have long tube headers, yours actually I don't have any exhaust leaks.
I'm currently running the pink springs, which are one step down from the stiffest set.
Seems timing related to me, since the ping became barely audible right after I retarded it a little.