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I have a Duraspark II distributor that is calibrated with 20 degrees mechanical advance built in. I have it set at 14 degrees BTDC and I get a vacuum reading of 22 at idle. This setting gives me great throttle response and low-end power, with no "kick back" on the starter at all.
20 mechanical +14 initial = 34 degrees total timing all in at 3,000 RPM. Engine specs are in my signature below.
I experience minor "pinging" ONLY when I put the pedal to the metal at wide-open throttle - but sometimes it doesn't ping even then.
I am not sure where to start. This engine runs FANTASTIC, and by that I mean every bit as good as any modern fuel injected vehicle. And it actually starts up even FASTER, so I really hate to mess with it too much.
Where is the best place to start? Too much total timing? Vacuum advance needs to be adjusted? Are the secondary jets too lean?
It isn't the vacuum advance, or shouldn't be, because at WOT the vacuum should be well below the point where the advance comes in. In fact it should be close to 0 and the vacuum advance probably drops out around 10".
So, it is probably too much overall advance, and you can most easily fix that by backing off initial timing as adjusting the distributor's advance isn't easy. However, the "probably" is in there because it is sometimes possible to stop pinging with a bit more fuel. But, tell us more about where in the RPM range the pinging comes - before the secondaries open? After? About red-line?
So, it is probably too much overall advance, and you can most easily fix that by backing off initial timing as adjusting the distributor's advance isn't easy. However, the "probably" is in there because it is sometimes possible to stop pinging with a bit more fuel. But, tell us more about where in the RPM range the pinging comes - before the secondaries open? After? About red-line?
OK, that rules out the vacuum advance then. How do the other timing figures look?
During normal driving and even casually passing another vehicle, I don't get any pinging whatsoever. But if I give it full throttle and the gas pedal is on the floor, I get very slight pinging almost immediately and continuously until I let off the gas again. I assume that is when the secondaries come in.
Do I need to fatten up the secondaries? How can I determine if that is the problem? As it is now, I don't experience any hesitations or flat spots at WOT.
The secondaries should come in somewhere around 3000 RPM, although they are brought in by air flow rather than RPM, but there's a direct relationship. So, the secondaries should come in well before you let off the gas - assuming you are winding that 302 up, as you should.
So, if you get pinging all the way up then either the carb is lean or you have too much advance. But it is unusual for a 4bbl to be lean when the secondaries come in. So, I agree with Old Hickory - back the timing off a bit and try it again.
I would try backing of the initial timing set from 14 to 12 and see it it makes any
difference.
Do you know what the staic compression ratio is on your engine?
Sorry, I don't know what the compression ratio is. I run 93 octane gas in this engine. The only reason is because there is a local gas station nearby that still sells 100% gasoline, (no ethanol) but only in 93 octane. And my truck is carbureted and only gets driven one or twice a week, so I don't want the ethanol gas just sitting there and eating up my carburetor gaskets.
I don't think my somewhat mild engine should "ping" with 34 degrees total advance with 93 octane, do you?
What do the plugs look like? If your plugs are too hot, which usually shows up as white insulators, then they can be the cause of the pinging.
But, we do need to establish that the secondaries on the carb are coming in and that the pinging continues when they do. That's because it is very rare for the air/fuel mix not to go fairly rich when the secondaries come in. So, if the engine keeps pinging when the secondaries come open the pinging isn't likely to be due to a lean air/fuel mix.
Can you feel the secondaries come in? Have you pulled a plug to see what the insulator looks like?
I wouldn't think you would have pinging with 93 octane gas but it can happen.
An overbore and swapping heads can sometime increase compression and the cam
you are running is not the type that will bleed off compression in that it is more of
a torque type cam.
Before you change anything on the carburetor, retard the initial setting by 2 degrees
and try it and see how the engine reacts. Retarding the timing has the effect of
a richer mixture just as advancing timing will lean it out.
As Gary and others mentioned, pull the plugs, keep them in order as to what cylinder they came from and do a good examination of them. They can tell you
a lot.
Line all the plugs up as they go in the engine and use a camera that has a macro setting to take their pic. Good lighting and a crisp pic will tell us a lot. But you don't want a lot of idling just before you pull the plugs as that can hide the "color" that they acquire while cruising.
Were your heads cc'd? If so, do you know what pistons were used? What head gasket? I'm wondering what your compression ratio is.
And, do you know if your secondaries are opening? I ask because if they are and it pings even then you probably don't have a lean air/fuel ratio. The majority of carbs I've played with are on the rich side at WOT, but it is possible the carb was jetted too lean, and that can play into a ping. It doesn't really cause the ping, but a rich condition will usually kill a minor ping, so lean can exacerbate one.
With the exception of #8 those plugs look like either the carb is too lean or the plugs are too hot. You should really have a light tan center electrode, and those look white to pinkish. If your secondaries are opening and it is still pinging then I'd bet the carb isn't too lean. So that tells me the plugs are too hot.
My vote would be to install the next notch cooler plug and see what that does. You can do as OH said and dial the initial lead back 2 degrees. But, if it were me I'd want to know if it is the plugs or the timing because if cooler plugs will do it then you can still run the 14 degrees and get the performance you have been getting.
But, we ought to hear the answers to Ken's questions as they may influence things.
You said the ping is at WOT, but at what rpm & load?
I drove it today, and the ping is still there, although very slight. I don't know what RPM, because my tach sticks when it is cold outside.
I haven't put this truck under a load yet, just when I nail the gas on a flat road, especially if I am in 1st or 2nd gear. I put the pedal to the floor and the engine revs up and a slow, lazy "marbles in a can" sound is heard. I barely hear anything (and sometimes nothing at all) when I punch it in 3rd gear or overdrive. Does that mean anything?
Originally Posted by Gary Lewis
If your secondaries are opening and it is still pinging then I'd bet the carb isn't too lean. So that tells me the plugs are too hot.
I definitely feel a PUNCH when I hit the gas, but how can I tell for sure if the secondaries are opening?
Originally Posted by Gary Lewis
My vote would be to install the next notch cooler plug and see what that does. You can do as OH said and dial the initial lead back 2 degrees.
The plugs I am running are Motorcraft SP415 (ASF-32C), which are already 1 step colder than the stock Motorcraft SP450 (ASF-42C) plugs.
Should I really go colder than that?
Why would these plugs run hot in my engine?
Originally Posted by Gary Lewis
But, if it were me I'd want to know if it is the plugs or the timing because if cooler plugs will do it then you can still run the 14 degrees and get the performance you have been getting.
I agree with you. But what is the next step colder plug from the Motorcraft ASF-32C?
