Ignition, vacuum advance question

Mikael,
I'm no expert but have been messing around with my dizzy the last few weeks so here goes.
First off the vac reading is to low for a stock motor, if it's been modified with a hot cam then it could read lower than the 18in. normal reading but if your running the 600 carb than I assume it's fairly stock. Is the 14in. at idle and manifold vac? Do you get the same reading cold or hot engine? Is the needle steady or drifting, pulsing, vibrating?
Here's some general info on low vac.

Low vacuum readings may indicate intake valve, manifold, or carb gasket leaks including internal or external manifold leaks. Spray carb cleaner around suspected areas to test for leaks.
Plugged catalytic converters, stuck heat riser valves, plugged intake crossover heat passages, crushed exhaust pipes, plugged mufflers, (check out that mouse nest in the exhaust!), and similar restrictions will usually lead to very low vacuum readings.
Excessively carbon in engines or those that did not get their oil changed often enough may result in sudden vacuum reading changes when valves stick. It could happen at any engine speed and may temporarily cure itself by quickly changing engine speeds.
Lower vacuum readings directly related to engine misfiring may be a result of a burned exhaust valve.
Constantly changing vacuum readings at low engine speeds may indicate a problem with worn valve stems, guides, or seals. Higher engine speeds tend to temporarily cancel out this problem.
High-speed vacuum readings that change may be a result of broken or tired valve springs, while low engine speed vacuum readings tend to be constant.
High performance or race cams tend to result in lower vacuum readings.

The burnt exhaust valve is high on my list.
Do a compression check on the cylinders.
Cowboy from Hell wrote:
My advice is that you do not need a timing light. Start by connecting the vacuum advance to ported vacuum. Leave the vacuum retard disconnected. Loosen the distributor locking bolt enough to allow adjustment. Start the motor, let it idle, once up to operating temp, slowly rotate the distributor in the advance direction. (clockwise). As you rotate the distributor, the idle speed will increase, continue to slowly rotate the distributor until you just reach the point where the idle speed stops increasing. This is the ideal advance setting for idle, and it will be significantly different than the specified setting from Ford. Ford’s setting was derived to meet emissions, it never was an ideal setting. If you’ve modified the motor in any way, the oem setting no longer applies anyway.

I think I'm at 18in BTDC. Your description off idle sounds to advanced.

If you have a dial back timing light see what your advance is at the 1000(0 advance), 1500, 2500, and 3000 (all in?)RPM speeds.

Steve

Hi Steve, thanks for lengthy mail.

I may just have solved most of it actually. I've disconnected the vacuum advance. Then I only had a problem in high rpm. I opened the distributor, and even though the instructions said that it was factory set to max 24 degrees centrifugal advance, it was well above 30. I corrected to 20, som now I can have 14 degrees at idle and 34 degrees total. I haven't had a chance to drive the car, but pushing the rpm in my garage (lucky neighbours) sounded like the problem was gone.

The vacuum reading is a bit low, now 16. I'm not sure why. I've tested the manifold/engine, I have a new carb with new gaskets and tried spraying. No result. And engine runs fine now. By the way, the needle is super steady, so I don't suspect major problems in the engine.

It doesn't go as fast as I thought, 0-60 in 9 seconds, but that was before fiddling with the advance, should be better now.

I need to test drive, will not happen until Monday earliest.

16 if it steady is about right. 18 would be perfect.

Turn up the distributor advance at idle and see if it goes up.

I would set the initial idle higher, like 16 and limit the total advance to 36. If it pings a little you could restrict the internal distribtor advance with a slip over sleeve on the advace limiting post.

It may not be the total advance that is causing a ping. It may be the rate at which it advances.

You should have full ignition advance at 2500 distributor rpm, 5,000 engine rpm. If it is in sooner then the octane of todays pump gas can't handle it.

quote:

If it is in sooner then the octane of todays pump gas can't handle it.

Does this apply here in Europe where we use 95 octane unleaded?

...Your Vacuum Advance should be connected to a 'Manifold' Vacuum source! Continuous at idle, but decreases slightly when the throttle is cracked and opened further. The way You have It connected now, to 'Ported' Vacuum; the 'Initial' is already set, But as You crack the Throttle the 'Port' Vacuum Increases, the Vacuum Advance Increases, as the RPM rises the 'Centrifical' Advance Increases; ALL added together It is Too Much advance at Cruising speed and above!...

...So Yes! Keep the Vacuum Advance for better Fuel Economy! Yes! You can adjust Most Vacuum advances Through the Vacuum Port of the Advance 'Canister' using an 'Allen' Wrench, to increase or decrease! No worries about loosing the 'Total' advance! As the Vacuum advance Decreases because of a Lower Vacuum Signal from Opening the Throttle; The Centrifical Advance will Increase because of The Increase in RPM from opening That Throttle! Check Your timing at 3500 RPM (But WITH the Vacuum Advance CONNECTED; and all of the Centrifical Advance is 'IN', NOW set the TOTAL Advance at 36-38 Degrees Before Top Dead Center. You can also Rev the Engine to 3500 RPM, Advance the Distributor Until Pinging is heard, then Back off the Distributor 2 Degrees. This is Called 'Power Timing' And Allows the Engine to 'Tell' You Exactly Where It wants the Timing to Run!...

quote:

Originally posted by No Quarter:

quote:

If it is in sooner then the octane of todays pump gas can't handle it.

Does this apply here in Europe where we use 95 octane unleaded?

I can not speak for what is sold in Europe. I do know that I stopped using 100 octane unleaded racing gas. For my set up it runs like 93 octane.

It doesn't allow for any more advance before pinging then the pump gas does either.

I honestly don't know what the value is for it other then costing $8 per gallon.

My personal preferance on the distributor timing would be to set initial at 16 and limit total distributor to 20. Just setting initial to 16 I'll bet will bring your vacuum back to 18.

You need to experiment with the advance springs to find the optimum advance rate. The curve that they supplied you with is the stereo typical for a SB Chevy. If you have open chamber heads I think that is what you want but the closed chamber heads will ping like a champ.

Like Marlin said you don't want to reduce the total advance under 34. 36 would be perfect if you can achieve it.

I have found that yes you want to run the vacuum advance off of manifold vacuum, absolutely correct, but with a fast advance curve in the distributor, if you can run more then about 6 inches in the vaccuum can, I'd be very surprized.

The most common Ford factory vacuum cans are going to be about 14 inches. Don't worry though. They are adjustable with the allen wrench through the vacuum tube.

[QUOTE]Originally posted by No Quarter: Just added a Summit electronic distributor,SUM-850306 to my 351C/Longchamp. I set it w/o vacuum advance to 16 degrees. I noticed the engine had to fight preignition when starting, so I changed that to 12 degrees. Cars seems to run fine, steady idle and takes the gas fine. Vacuum however is only 14. Then I added the vacuum advance, taken from the port vacuum on the Holley 600. Idle unchanged (of course, it's ported vacuum), but when accelerating it pings and explodes in the exhaust, clearly too much advance.

Mikael, are you sure the harmonic balencer's timimg mark is correct? Its rare that a factory harmonic balencer hasn't shifted- always to the retard side. I have quite a collection of junk balencers, all with the mark moved. One is 160 degrees out! If the engine's 'fighting' the starter, you have way too much initial advance! A second thing that will cause popping under acceleration is a cold engine. Before hammering the accelerator pedal, be sure the engine is smoking-hot. A third thing is a too-stiff secondary diaphragm spring if the carb is a common vacuum-secondary Holley. Finally, don't get too locked into a particular number for advance. Just adjust the intial advance, drive the car and see if you can hear any engine rattling. If not, add a few degrees until you can hear pre-ignition or detonation. Then back off a degree of two and call the job done. Not all combinations of Clevelands behave the same. FIWIW, Euro octane ratings are measured differently than the U.S: 95 euro-octane is about 91 U.S.- what we call 'premium'.

Marlin and Doug,
I'm a little confused about the Ported vs Manifold Vacuum for the Dizzy. It seems up to this string(search of the archives) everyone was saying use the PORTED connection on the carb for the Vac canister. Is the general consensus now to use the Manifold??
Steve in Va