So, for several years my 1969, base engine with 74k miles, has been knocking/pinging when you give it enough gas for the secondaries to open up on the carb. Here is a list of everything that I have tried and what has been tried/changed:

Before I got the car:
MSD distributor 8572 installed 3 years ago.
Holley 6210-3 Carb (replaced about 5 years ago. Had one on it since 1973)
had wrong spark plugs installed

Since I have had the car:
Replaced with spark plugs R43S AC Delco
Replaced PCV Valve
Found that we probably have valve seal leaks (oil on the spark plugs)

Current distributor settings:
Currently has 28deg bushing, vac advnce lockout, blue springs (total timing doesn't kick in until ~4000rpm)
Current timing 0deg (I need to verify this, info from my dad)

From what I am thinking: probable cause of the knocking/pinging is caused by hotspots in the combustion chamber and or too much carbon built up over the years which has increased the compression ratio.

I am running 93oct with royal purple and techron.

Are there any other suggestions of what I can do? I might put on a larger bushing (25 or 21) and increase the base timing to help with the lower end which might help a bit but still wont fix the pinging/knocking

 

I remember reading that oil contamination in the combustion chamber can cause pinging. You could say oil has a lower octane rating than gas.

 

You need to check timing for total advance. Should be no more than 36, with vac advance disconnected, whenever full advance occurs in your case. Set for total advance, don't worry where it is at idle, as long as the car starts OK.

 

Could it need a bigger shot for the transition?

 

That is a good possibility! I really need to get the valve seals fixed ASAP.

 

Total advance should be mechanically limited to 28deg max with 0deg idle from what I have found on the docs for the distributor. I need to get the grommet for the pcv (it was loose) replaced and I am having issues finding one to fit the base 350/300hp valve covers. Then I will check the total timing

 

Thats a good possibility!

I think I need to work on:

new grommet for pcv (on the hunt for the moment... )
valve stem seals
timing adjustment (lower the mechanical advance and increase the starting point at idle)
then carb jets

after that, I think I am going to try to decarbon the engine (I have had the recommendation of running distilled water through using a valve control connected to a full vacuum source and cruise down the highway then slowly open the valve some)

 

"From what I am thinking: probable cause of the knocking/pinging is caused by hotspots in the combustion chamber and or too much carbon built up over the years which has increased the compression ratio."

No way, not at 74K miles. Also, valve seals won't cause it to ping unless they're so bad you're blowing lots of oil smoke out the pipes. Even at that, oil is sucked through the seals mostly when vacuum is high. That happens at idle and decel, not full throttle. Same for the PCV grommet; it won't cause this problem. Timing should be about 8 degs at idle. That will give 36 total if the paperwork you have is correct. Incidentally, have you checked to be sure TDC on the harmonic balancer really is TDC? That's really important on these older cars.

Other questions... Did you buy this car new? Was the carburetor new when you put it on the car? When did the problem start? Is the cam factory? Is it possible the pistons have been changed for a higher CR? Have you looked through the spark plug holes with a borescope to see what the chambers and pistons look like?

I strongly recommend that you not pull the heads or try any homemade remedies to "decarbon" the motor until you know exactly what's happening.

 

I suspect you do not have "0" as your base timing. It would run awful hot exhaust and not want to idle at that setting.

Figure out what your timing is and go from there. Also check you jetting on the secondaries, could be too lean.

Oil in the comubustion chamber is not good for these conditions, true in that it is drawn in from valve guides during high vacuum periods, but it is not flushed away with each power stroke so oil remains in the chamber for the next stroke.

This is what your intake valve will look like pretty quick with bad valve guide seals.



That was taken from my 350 that had worn valve guides and bad seals. It only showed a little smoke out the pipe during idle.

It is possible that you could have some carbon in the combustion chamber and water down the carb throat while holding the idle high ,after up to operating temps, is a legit way to break some of it loose.

 

Your timing specs are way off. If you're set up with 0 degrees at idle, your engine is running so hot it's probably pre-igniting like a diesel... Get your initial timing up into the low-teen range (12-ish is good for a stock engine) and then verify you get about 36 degrees total coming in around 3000-ish rpm. Then hook up your vacuum advance and limit it to about 12.

Lars

 

Looking at the instruction sheet for your distributor, combined with Lars suggestion, you need 1 light blue and 1 light silver spring and the silver stop bushing and set your initial timing to 11 degrees which will give you a total of 36 degrees mechanical.

http://static.summitracing.com/globa...2_frm28723.pdf

 

Vacuum advance lockout is a big mistake; engine is way too retarded for WOT at 2500-3000 rpm. Do what Lars suggested. Get that vacuum advance working and connect it to 'manifold' vacuum (not 'ported' vacuum).

 

So, the plan for the timing:

verify TDC on the balancer
order advance tuning kit (it wasn't in the parts when I got the card... but a ton of other things were)
order vac advance canister

Before I go into that though, I HAVE to get the valve stem seals fixed. I am also planning on pulling the carb and cleaning up the secondaries, replacing a fuel line which looks like it might be a restriction (between the filter and the carb).

Just so many little issues with this car and slowly fixing each one as time and money permits

 

I would verify TOP DEAD CENTER as a first step to make sure you're timing marks are correct.
If TDC is off you're timing is all guesswork.

There are numerous posts on how to do it at low / no cost - I like a piston stop.

Then I would follow Lars instructions..

 

TDC tool is on it's way.

Todo:

High Pri (not particularly in this order):
* pull and clean the carb (esp the secondaries) to verify I am not starved for fuel
* verify TDC
* Order advance kit for Dist
* Order Vac advance canister for dist
* Replace valve stem seals

* once TDC is verified and carb is cleaned, I will start the tuning with a lower advance stop bushing (18deg or something around that) along with softer springs to get things to total advance up around 3-3.5k rpm. I will then see where it is with those and tune as necessary changing out the advance stop bushing and adding vac advance.

Also why setup the vac advance with full vacuum and not ported? Wouldn't it give you full vac advance at idle?

 

Yes it will. Ported vac advance is for emission control. It makes for late ignition and hot cylinder and exhaust temps.

Full vacuum ignites the fuel early enough to burn more completely during times of low cylinder pressure and slow burning fuel. This would be at idle in regards to ported vs full vacuum. Also most other conditions other than WOT.

The goal is to achieve the most cylinder pressure about 15* or so after TDC. Cylinder pressures vary according to the conditions that the engine is under. WOT presents higher cylinder pressures, so the fuel burns faster. This allows us to ignite the charge later to achieve that max pressure after TDC. This is why vacuum can drop out at WOT and still give the best power.
Ignited too late and the fuel is burning too late in the cycle and may even still be burning in the exhaust pipe. That's power out the pipe.

Ignited too early and you have too much pressure BEFORE TDC fighting the piston to rise to TDC. This means the peak pressure is reached too early missing that 15* or so ATDC. Early enough and your cylinder pressure rises to the point of auto-igniting the fuel, aka, detonation. Good for diesels, bad for gas engines.

 

Ported vacuum will also give you higher cylinder temperature at idle and lead to run on when you shut the car down.

If you remember the problems in the 70's - most was from the lower compression and going to ported vacuum to reduce emissions at idle.

 

STATUS UPDATE:

Replaced Valve Stem Seals
Pulled and cleaned the carb (more on that in a bit), put in larger jets (83 stock, went to 86)
verified TDC
Purchased adjustable timing light, set everything for 10 initial, 25 mech adv, 35 total plus vac advance (I might add one more degree but everything is working at the moment)
I was getting crap for power above 3k rpm and it was smoking quite a bit... wtf?

after checking and rechecking timing, oil, everything... bought 84's and put them in... same thing. Went back to stock with 83's same thing... WTF? after looking and looking and looking, I thought maybe fuel filter related... replaced the inline then went to replace the internal and pulled the primary bowl.... I see only one jet installed. DOH! I only put in one of the primary jets so it was DUMPING fuel on half throttle. Put the correct jet back in and holy shhhnnnniiittt it runs well now. That extra fuel also probably cleaned up all of the carbon off of the valves and everything. Had an oil change to get the fuel which had run down and contaminated the oil and it runs like a bat out of hell now. Now to track down the dreaded vacuum leaks (very slight leaks but still want to fix them) to help with off the line power. Right now I have the idle mixture screws at 3.5 turns out... probably due to the leaks.

 

It has been suggested on here to disconnect the vac line to the head lights and wipers at the intake manifold "T" behind the carb and plug the fitting.
Then do you engine tuning ritual.
If you have leaks in the headlight and wiper system they will reappear in the quality of the idle when you hook the line back up.
A healthy motor is anything above 16hgs of vac at idle.
Marshal

 

I am getting around 21hgs at the moment. It was at 20 with 2 turns out