I've had an issue with pinging ever since I've rebuilt my engine. From what I've read online, I'm concluding that I'm lean on my fuel mixture. Backing down timing doesn't fix it all the way, and running high octane doesn't help either. I'm running a Holley 2300 carb that was on it when it was 292. Now I'm at 312. The pistons are down in the hole at TDC so I'm sure the compression isn't too high. Is there a formula of some sort to determine which jets I should be running? I pulled 1 out and it is number 50.

 

There is, but it's kind of complicated. Ask here:

Racing Fuel Systems - Holley

What plugs are you running, and what do the usual indicators look like? #50 jets should at least be in the ballpark. I suppose it's at least possible too hot a plug would cause pre-detonation, this isn't the same as engine knock and very destructive. Maybe doubtful, something to beware of. Usually too lean jetting will also cause noticeable surging at steady part throttle speeds. Another consideration for engine knock is a defective distributor itself. Is it new or NOS, chinesium special, rebuilt? Running points?

 

I'm running #46 autolite plugs. The distributor is a Autozone special that I've been running about 5 yrs now. I put Pertronics unit in it about 2yrs ago. Running a stock coil. Engine rebuilt last year. Never had this issue before the rebuild. So that's why I was looking at jets. The carb is rated to be run on engines at big as 390. Can the cam play anywhere in this?

 

Are you sure your dampner ring hasn't slipped and giving you a false timing reading?

 

Interesting problem. The ping or engine knock, it's the full on rattle accelerating under load type, correct? This is why I mentioned distributor, once they get loosey-goosey in the bushings it usually requires backing off on the specified timing, or, if the breaker advance plate is sticking that will do it too.

 

I thought of that too, but he says he rebuilt engine. Guess I shouldn't assume anything though.

A mechanic's vacuum gauge would be a good diagnostic. How much is the engine pulling at idle? 18" to 20" at sea level, although a hotter cam will reduce this number.

 

Too radical of a cam could play into it, what cam? I don't know where Parma is, what type of fuel? My 292 is +060, G heads and an Isky E4 cam and runs fine on mid grade 89 octane California crap fuel with 10 degrees initial timing.

 

Post a clear close up pic of a spark plug head on and maybe from the side, showing of the ground strap. Heat range, jetting, ignition timing, pre-detonation and other things will show up when you know what to look for. There should be a color transition line on the ground strap about halfway when the heatrange is right. Modern gasoline does NOT "color" like it did back in the day though.

46 is a pretty hot plug, and recommended by some for around town driving (less fouling). For initial tuning though it's also recommended to start with a "stock" plug to get a baseline for heat range and jetting. I use a Pertronix Ignitor and a Flamethrower coil direct (full) battery voltage, and tuned the carb a little with a wideband and curved the distributor pretty tight. Just messing around, but what I found is a slightly cooler heat range prevents part throttle rattle in my particular setup that can be mistaken for excessive vacuum advance, this took me a while to figure out. I like NGK plugs, they have a wide selection range in any given plug #

Engine knock and pre-detonation are two different things with different causes, if the plug tip is too hot it will start the fire too early aka pre-detonation. Excess carbon will do this too. It's better to start out tuning with a plug on the cold side of things, and then work up incrementally to a hotter one. The worst that can happen with too cold a spark plug is fouling, too hot of a spark plug can cause permanent engine damage. I doubt this is the problem, but file it in the back of your mind for reference.

 

The plugs are fairly new, installed after the rebuild. That's what the computer told the geek at the store to sell me. I didn't know those were hot plugs. The damper is brand new, and I've advanced/retarded the timing on the side of the road with no change in the results. Interesting thought about the advance plate on the distributor. It pings on easy acceleration or hard. If cruising and just goose it a little it pings. Last week I was running Shell 93 octane in it. The cam is an Erson grind RV10M. The figures at
.050 tappet rise is .290 lift on intake/exhaust. 210 duration for both. 107 intake center line. overlap -12.00 There figures are based on 1.47 rocker. However, I'm running 1.54 rockers.
I'm in Parma, Ohio. 5 minutes from where Drew Carry grew up.

 

Maybe run it up with a timing light w/ vacuum advance port disconnected and plugged.

See that the timing marks move smoothly all the way to your max timing and back down again to the same base idle timing without "scatter" or sticking/hanging.

Then do the same with vacuum advance re-connected. Might see almost 50° BTDC with the latter as there is no load on the engine in neutral, but everything should move freely and fast and return to base when throttle is closed.

 

Check with the timing light how much advance vs rpm. It maybe something as simple as a weak or broken advance spring that is letting it advance too soon at lower rpm.

 

A friend of mine says that now that I'm running headers instead of stock exhaust, I should give some more fuel. Never heard that one before. I pulled 3 plugs out. I've never learned the art of reading them, so here's some pics.

#1 cylinder

#2 cylinder. Looks a little fouled

#3 cylinder

 

Those are kinda blurry pics, though the plugs certainly don't indicate lean running.

I'm still circling around to the distributor. Defective distributors will not allow for the correct mechanical advance settings when they get sloppy, it will ping or knock because of poor control of the timing event. The "fix" is then to retard the ignition timing, which hurts performance and economy. If the breaker plate plate is sticky, that will only add to the issue. Apply vacuum to the hose and observe that it moves freely or not. Does it idle smoothly? When distributors get loosey goosey it will usually not not idle very well and the igntion patterns shake like an out of balance washing machine. "Rebuilt" distributors are are a total crapshoot with an emphasis on the "crap" part.

The only way to really tell if the distributor shaft and bush has excessive wobble short of using a scope is if the reluctor arm is removed and check for excessive sideplay of the shaft itself. Pertronix is less affected by this because it is electronic but it is not immune. 5 years ago they were also selling lots of "counterfeit" Y-block distributors in the remanufactured parts world. Be sure to check for this, the dimensions are not correct for correct engagement of the distributor gear with the camshaft gear nor the pump rod, I'd bet you a cup of coffee they gave you one of those, too.

For tuning you want a good baseline measurement of everything. I'd suggest a cylinder compression test. Also vacuum gauge readings, engine manifold vacuum on the gauge shows an amazing amount of information. It is practically indispensable, I don't know how anyone would diagnose or tune up an engine without one. Keep a logbook of everything as you go along to keep track.