The racer idles at 2,200 RPM. Adjusting timing at just off idle can be misleading. At idle and close to idle there is nearly no cylinder filling, so the effective compression is very low, (say 5 to 1) so little heat of compression, low fuel supply, and poor flame propagation. Also the engine runs poorly when first started, but then runs fine when warm??

 

Because better vaporization comes with rotor face temperatures and better more complete fuel burn and a bit more power. So typical controllers richen during cold coolant temps to compensate. Also advance my be reduced along with that temperature increase. Since there is so little fuel involved stresses are low and there is little chance of any kind of damage.

 

To find out what is ideal for each condition I would keep advancing ignition as long as RPM keeps increasing. Then when RPM does not increase with the next change, back up three changes and make that a set point for that air temperature/coolant temp.

 

The problem is that beyond "just off idle" as you crack the throttle to begin to taxi, for example, the cylinder filling shoots way up close to 100%, so the effective compression ratio becomes 9.7 to 1 and your newly tuned in idle advance setting of say 27 degrees is now way too much advance for a slow turning engine with 100% cylinder filling.

 

Perhaps 16, 18 or 20 degrees would be much better now and even then only with light loading. It is difficult to see but timing is based on RPM, and at low RPM you can achieve a complete fuel burn well before TDC and that would give you highest cylinder pressure well before 50 degrees ATDC. So if there is no system to pull out advance with sudden throttle opening, you are stuck with a lower fixed advance setting.

 

The racer is set at fixed, 25 degrees for 93 Octane motor fuel. And that is for best power at 9,400 RPM. The car is not operated even in low gear with that advance unless the car is going out onto the track. Then the clutch is slipped until the car is rolling and is nursed slowly up to speed in first gear before much throttle is used.  First gear is good for 70 MPH. The car is towed around the paddock with a little tractor called Deer John.  

 

Lynn E. Hanover 

 

 

 

Going up to 28*, the RPM hung around 1905.  Dropping back to 23.3, brought me down to about 1880.  19.6 got me 1860, and 15.6 produced 1830.  Now, these aren't exact numbers...more of an eyeball average, but 15 degrees of advance only made about 75RPM difference.

The trade-off is that more advance means more stress on the system, and more heat in the coolant. Would it make sense to accept the power loss, and dump the heat out the exhaust, or should I keep searching above 28 for more power?  Other than a backfire and a broken apex seal, what signs would the engine give you that it has all the advance that it really wants?