18 replies to this topic

[dklawson]

If you are going to experiment with the timing settings, invest in an advance (dial back) timing light as opposed to the "regular" type.  With the advance light you can start thinking about your timing from the top down instead of from idle up.

• Bring the engine to temperature. 
• Connect the advance timing light and set it for 32 degrees.
• Use the carb's idle screw to bring the engine speed up to 4000 RPM.
• Adjust your distributor position until your ZERO timing mark lines up.  (Remember... the light is set to 32 degrees)
• Lock the distributor down and return the idle speed to normal.
• Drive the car placing it under heavy load by doing something like driving uphill in too high a gear.  Try to make it knock and ping.
• If any knocking or pinging is heard, retard the timing by 2 degrees from what it is and repeat the test drive.  Do this until no more knocking or pinging is heard.

At 4000 RPM all of your distributor's mechanical advance should have taken place.  Setting the spark timing with the mechanical advance fully on will set the max advance your engine can handle for its state of build, general condition, and the grade of fuel you are using.  As long as you do not change anything (including the grade of fuel you buy) you can then measure the idle speed and idle speed advance using the timing light and tach.  You can use those as your settings for future (idle speed) tune ups.  

 

This would not apply to the CSI or 123 distributors with their own unique built in electronic advance curves.  For those products, follow the manufacturer's method of setting the ignition timing.  Obviously this method also has no application on mapped ignition systems.

[ohsuchislife]

mate your a star going to put my standard dizzy in with electronic ignition and ply around a bit ... waiting for cam thrust to turn up aaaggggghhhhhhhh

[carbon]

sorry to op,, but from Carbon's comments

 

so you are basically running 18 degree static and 28 at what...... how did you come up with this solution... i have seen some hi static timing used in bathtubed heads?

it is interesting because i have a kent clone 266 and it seems to prefer higher static but i have been scratching my head at readings....(1310) i may go back and put a stop on the mechanical and see how it goes advanced.  Cheers

 

Here is the approximate total ignition timing I am running with 12 degrees static, expressed as degrees advance at the crank.

 

Rpm at crank       Total advance at crank

0 (static)                  12

800 (idle)                 18

3500                        32

 

Advance at idle is estimated. Static is accurate, set up using flywheel markings. Total advance of 32 degrees is from static plus 2 x 10 degrees of mechanical advance in the 41257 distributor.

 

Lighter primary advance spring (41238 primary) controls advance in the first 0-10 degress of mech advance, this comes in quickly. Then from about 1200 rpm the secondary spring (41257 secondary) brings in the next 10 deg mechanical advance which is probably all in by 3,500 rpm. Distributor is a 25D4 using vacuum advance with 4-11-7 can.

 

I have never had this unit on the rolling road, so likely still room for improvement. However despite the pretty brutal advance curve there is no sign of pinking using Shell 99 octane. This is a 1293 using CR of about 9.75:1

 

Above settings pull much better mid-range than before when I had a much gentler advance curve. Idle is also better and engine seems to be running cooler than before.

[Earwax]

thanks Carbon   - excellent info - including all the spring vac info - i think i will rebuild one of my dizzies in a similar fashion.  I have always thought that steep advance curves worked best for my 1275.  ( 23-24 at 2000rpm) Cheers