Timing Curve

[PaulProe]

As I begin my journey down the tuning path, I find my distributor isn't advancing as it should. No big deal, my money pit has gotten lonely so I throw a few more bucks into it.

The question now is what is the preferred curve for a set of webers. I know that 38degrees on an FE is where the thing wants to be, but at what speed? When do I need it all to come in. Any tips on length of advance? I was thinking 24 so I could set the base at 14 to make it easier to start and then top off at 38.

My idle speed is around 850 so when to I want the advance to begin and how much when? - the curve isn't a straight line. Mallory has all kinds of settings, probably 20 more than what I need.

Any suggestions on where to start?

Paul

[DesertMK4]

It is my understanding that the timing is set per specs on the engine, and more so due to the cam in that engine. Most engines have a base advance (usually 15-20 degrees) and a maximum advance (usually 30-40 degrees). A mechanical distributor should have springs and limiters to control the advance curve. With a vacuum advance there usually is some way to modify the curve but to a lesser degree than with a mechanical advance. The carbs have very little to do with ignition timing. Mostly its a matter of trial and error to set up your timing for your use of the car (race, street, etc.).
For street use a mechanical/vacuum advance may work better as a mechanical system advances in a more straight line whereas the vacuum advance responds to vacuum (load). One may "smooth" out the other.
Base timing is set at idle so what you idle at makes no difference. If vacuum advance only you must disconnect the vacuum to set the base. With mechanical/vacuum the vacuum port on the carb (Holley) does not pull a vacuum at idle.
Advance "all in" RPM is also engine dependent. Most Ford engines are "all in" at about 3500-4000 RPM.
It took me about 3 weeks to work mine out on a Ford crate engine. I ended up at base 18 degrees BTDC and topped out at 38 degrees. I have a mechanical/vacuum distributor.
Good luck with yours

[PaulProe]

Originally Posted by DesertMK4

. . . Most Ford engines are "all in" at about 3500-4000 RPM.

That seems like a Little Old Lady setting. I am seeing 2500-3000 tops.

Any other opinions out there?

Paul

[Rick Parker]

Webers like ignition advance typically about 18 degrees at about 900 RPM idle, all (36-38) in by about 2600 RPM.

[PaulProe]

Originally Posted by Rick Parker

Webers like ignition advance typically about 18 degrees at about 900 RPM idle, all (36-38) in by about 2600 RPM.

Rick
With that high an initial advance, do you run into hot start issues?

I use a PowerMaster 9606 starter, and there are times it really doesn't like 14 degrees.

?

Paul

[Rick Parker]

In think there a FE owners that use numbers close if not identical to that. Maybe Saltshaker can chime in?
Mine is 289 with Tilton starter.
In the 70's I had an acquaintance with a dry sumped SBC in a Gurney Eagle Can Am car. The engine was so low and chassis tight that the starter was remote mounted and run off of a shaft with a u joint in it. Several times it broke the U Joint while attempting to start. Finally we installed a switch on the dash that grounded the primary side of the ignition until it was spinning sufficiently then the switch was flipped creating spark and it would the start.

[wolf k]

Hi Paul,
I also can confirm that webers like a lot of initial timing advance. At least on a small block, I am at 22 deg at idle, 36 deg at 2700 rpm. No starting issues, in fact it starts immediately, and settles to a nice idle almost as quickly as an injected motor. I spent a lot of time with different curves and initial settings, and this is where my engine seems to perform best. Engine has 10.5 compression, mild cam.
I have always wondered why webers on IR manifold need a lot of initial timing. Perhaps they do not atomize fuel as well as a single carb on a manifold at low engine speeds?
When you say your starter has a hard time at 14 deg, do mean with your current weber set up, or your old 4bbl set up? And we are also just talking about mechanical only adv. distributor, not vacuum correct?
Wolfgang

[saltshaker]

18 int / 36 total all in by 2600rpm
Jon